Scientia World

Stars create complex organic molecules

2011-10-28T03:48:00.000-07:00

Complex organic molecules like those on which life is based exist throughout the universe and can be made naturally by stars, European Space Agency data has revealed.
Professor Sun Kwok and Dr Yong Zhang of the University of Hong Kong say they've found compounds so complex that their chemical structures resemble those of coal and petroleum.
The find suggests that complex organic compounds can be synthesized in space without the presence of life forms.
"Our work has shown that stars have no problem making complex organic compounds under near-vacuum conditions," says Kwok. "Theoretically, this is impossible, but observationally we can see it happening."
The researchers were investigating a set of infrared emissions detected in stars, interstellar space and galaxies, and known as Unidentified Infrared Emission features.
These signatures were believed to have come from simple organic molecules made of carbon and hydrogen atoms, called polycyclic aromatic hydrocarbon (PAH) molecules.
But, using the Infrared Space Observatory and the Spitzer Space Telescope, Kwok and Zhang discovered that the spectra have features that can't be explained by PAH molecules.
Instead, they say, the substances generating these infrared emissions have chemical structures that are much more complex.
Analysis of the spectra of star dust formed in novae shows that stars are making these complex organic compounds in a matter of weeks, and then ejecting it into the general interstellar space.
Interestingly, this organic star dust is similar in structure to the complex organic compounds found in meteorites, and could form their source. Thus, it's possible that life on Earth developed from this organic star dust

Battered asteroid Lutetia revealed as ancient baby planet that never fully formed

2011-10-28T03:45:00.000-07:00

A battered, pockmarked object floating in the asteroid belt between Mars and Jupiter has been revealed as an ancient fledging planet, formed when Earth was in its infancy.
The European Space Agency’s comet-hunting probe Rosetta flew past the asteroid Lutetia last year and studied it with thermal and spectroscopic sensors.
What it discovered is that Lutetia is no ordinary asteroid – but actually a primitive ‘mini-world’ that used to be round and may even have tried to grow a metal heart like a fully formed planet.

For the crater good: Lutetia has been revealed as a fledgling planet containing huge amounts of iron that was around when Earth was born

Astronomers believe that Lutetia should really be described as a planetesimal, a body formed from clumps of cosmic grains.

These have the potential to grow into planets, because once they reach around 3,000 feet in width they develop gravity that can attract other masses.
Asteroids, on the other hand, are formed from collisions between planets and other asteroids.
Rosetta flew past Lutetia on 10 July 2010 at a speed of nine miles a second and came within 1,969 miles of it.

Heavenly body: The ESA's Rosetta probe analysed Lutetia with thermal and spectroscopic sensors to reveal that it is no ordinary floating rock

At the time, the 80-mile-long asteroid was the largest encountered by a spacecraft.
Images from Rosetta’s instruments reveal that parts of Lutetia’s surface are around 3.6billion years old.
Other parts are young by astronomical standards, at 50 to 80million years old.
Astronomers estimate the age of airless planets, moons, and asteroids by counting craters.
Each bowl-shaped depression on the surface is made by an impact. The older the surface, the more impacts it will have accumulated.

Exploration: An artist's rendition shows the Rosetta orbiter, top, and lander, which it uses to reach the surface of comets

Some parts of Lutetia are heavily cratered, implying that it is very old.
On the other hand, the youngest areas of Lutetia are landslides, probably triggered by the vibrations from particularly jarring nearby impacts.
Debris resulting from these many impacts now lies across the surface as a 3,000ft-thick layer of pulverised rock.
There are also boulders strewn across the surface: some are 1,300-feet across, or about half the size of Ayers Rock, in Australia.
Some impacts must have been so large that they broke off whole chunks of Lutetia, gradually sculpting it into the battered wreck we see today.
‘We don’t think Lutetia was born looking like this,’ says Holger Sierks, Max-Planck-Institut für Sonnensystemforschung, Lindau, Germany. ‘It was probably round when it formed.’
Rosetta also let scientists investigate beneath the asteroid’s surface.
It appears that Lutetia tried to grow an iron core like a bona-fide planet when it formed.

Ready for take-off: Rosetta was launched on board the Ariane-5 launcher from the European Spaceport in Kourou, French Guiana, in 2004

During the encounter, Lutetia’s weak gravity tugged on Rosetta. The slight change in Rosetta’s path was reflected in radio signals received back at Earth, indicating a mass of 1.7 million billion tons.
This was a surprise.
‘The mass was lower than expected. Ground-based observations had suggested much higher values,’ says Martin Pätzold, Universität zu Köln, Germany, leader of the radio science team.
Nevertheless, when combined with its volume, Lutetia still turns out to have one of the highest densities of any known asteroid: 3400 kg per cubic meter.
The density implies that Lutetia contains significant quantities of iron, but not necessarily in a fully formed core.
To form an iron core, Lutetia would have had to melt as a result of heat released by radioactive isotopes in its rocks. The dense iron would then sink to the centre and the rocky material would float to the top.
However, Lutetia’s spectrometer indicates that the body’s surface composition remains entirely primordial, displaying none of the rocky material expected to form during such a molten phase.
The only explanation appears to be that Lutetia was subjected to some internal heating early in its history but did not melt completely and so did not end up with a well-defined iron core.
These results, all gathered during just a short flyby, make Lutetia a unique asteroid and an invaluable postcard from the past, at a time when Earth was forming.
‘We picked a most important member of the asteroid belt,’ said Rita Schulz, ESA’s Rosetta Project Scientist. ‘All the asteroids encountered so far were different from each other, but Lutetia is the only one in which both primordial and differentiation features have been found.
‘These unexpected results clearly show that there is still much more to investigate before we understand the belt fully.’
Having now left Lutetia far behind, Rosetta is in hibernation and en route to its 2014 rendezvous with comet Churyumov-Gerasimenko.

Space science

2011-10-25T03:58:00.000-07:00

The term space science may mean:

The study of issues specifically related to space travel and space exploration, including space medicine.
Science performed in outer space
The study of everything in outer space;this is sometimes called astronomy, but more recently astronomy can also be regarded as a division of broader space science, which has grown to include other related fields.

This article describes the third meaning, space science describing all of the various science fields that are concerned with the study of the Universe, generally also meaning "excluding the Earth" and "outside of the Earth's atmosphere".

Divisions of space science

One proposed timeline of the origin of space, from physical cosmology.

By subject

Stellar astronomy - the study of stars
- Solar astronomy - the study of our Sun
Planetary science - the study of planets, especially those other than Earth
Galactic astronomy - the study of our Milky Way Galaxy
Extragalactic astronomy - the study of the larger universe beyond the Milky Way
Physical cosmology - the study of the origin, large-scale structure, and space-time relationships of the universe

Interdisciplinary fields

A simulated-color map of the surface of Venus as measured by synthetic aperture radar on the Magellan probe.

The Helix Nebula, NGC7293.

Comet Tempel 1 67 seconds after colliding with the Deep Impact probe.

Astrobiology
Astrochemistry or Cosmochemistry
Astrophysics - the intersection of physics and space science, the study of the physics of extraterrestrial objects and interstitial spaces
- Space plasma physics
- Orbital mechanics or astrodynamics, which also has applications to spacecraft
Planetary science - overlaps with Earth science
- Planetary geology
Micro-g environment research
Forensic astronomy
Space archaeology - the study of human artifacts in outer space
Archaeoastronomy - the history of human understanding of the universe
Astronautics is the science and engineering of spacefaring and spaceflight, a subset of Aerospace engineering (which includes atmospheric flight)
- Aerospace engineering
- Control engineering
- Orbital mechanics
- Spacecraft design for launch vehicles and satellites
- Space environment - study of conditions that affect the operation of spacecraft
- Spacecraft propulsion
- Space food
- Space logistics
- Space medicine

By approach

Observational astronomy - Observatories on the ground as well as space observatories take measurements of celestial entities and phenomena
- Astrometry - stuies the position and movements of celestial objects
- Amateur astronomy
Theoretical astronomy - mathematical modelling of celestial entities and phenomena

Related activities

Space exploration - includes scientific investigations through manned spaceflight and space probes
Space colonization
Commercialization of space
- Space manufacturing
- Space tourism
Space warfare
- Alien invasion
Asteroid-impact avoidance
Space law
Remote sensing
Planetarium - A synthetic observatory, used for education and presentations

Science, engineering and technology

2011-10-20T04:15:00.001-07:00

The distinction between science, engineering and technology is not always clear. Science is the reasoned investigation or study of phenomena, aimed at discovering enduring principles among elements of the phenomenal world by employing formal techniques such as the scientific method.Technologies are not usually exclusively products of science, because they have to satisfy requirements such as utility, usability and safety.
Engineering is the goal-oriented process of designing and making tools and systems to exploit natural phenomena for practical human means, often (but not always) using results and techniques from science. The development of technology may draw upon many fields of knowledge, including scientific, engineering, mathematical, linguistic, and historical knowledge, to achieve some practical result.
Technology is often a consequence of science and engineering — although technology as a human activity precedes the two fields. For example, science might study the flow of electrons in electrical conductors, by using already-existing tools and knowledge. This new-found knowledge may then be used by engineers to create new tools and machines, such as semiconductors, computers, and other forms of advanced technology. In this sense, scientists and engineers may both be considered technologists; the three fields are often considered as one for the purposes of research and reference.
The exact relations between science and technology in particular have been debated by scientists, historians, and policymakers in the late 20th century, in part because the debate can inform the funding of basic and applied science. In the immediate wake of World War II, for example, in the United States it was widely considered that technology was simply "applied science" and that to fund basic science was to reap technological results in due time. An articulation of this philosophy could be found explicitly in Vannevar Bush's treatise on postwar science policy, Science—The Endless Frontier: "New products, new industries, and more jobs require continuous additions to knowledge of the laws of nature... This essential new knowledge can be obtained only through basic scientific research." In the late-1960s, however, this view came under direct attack, leading towards initiatives to fund science for specific tasks (initiatives resisted by the scientific community). The issue remains contentious—though most analysts resist the model that technology simply is a result of scientific research.

The Science Breakthroughs that 2011 May Bring

2011-10-18T05:15:00.000-07:00

From discovering the so-called God particle and confirming the existence of an Earth-like exoplanet to understanding more about the brain and even defining a fourth domain of life, the science possibilities for 2011 are awe-inspiring.

Here's a look at some of what may come to bear in this year.

The Higgs boson – a particle so important to science that it's been dubbed "the God particle" – may come out of hiding in 2011.

This fundamental particle, thought to give mass to all particles, has been theorized since 1964 but never detected.

"If nature is kind to us, we will find it next year," said particle physicist Christoph Rembser, of the European Laboratory for Particle Physics (CERN) in Geneva, where the world's largest atom smasher, the Large Hadron Collider, went online in September 2008. With the atom smasher up and running, Rembser said physicists have everything they need to detect and measure the particle.

Offering an X Prize for brain breakthroughs

A $10 million prize to spur the creation of innovative neurotechnologies for the human brain could debut as soon as next year. The first possible challenge might be a Neuroeducation X Prize that seeks to dissect learning in the brain and eventually give a boost to the brains of students, or a Paralysis X Prize that promotes recovery of body functions in spinal cord-injured patients. Future X Prizes could even tackle far-out ideas such as virtual telepathy, allowing humans to effortlessly interface with computers using only their brains, and smaller X Challenge rewards could drive innovation for brain issues such as Alzheimer's disease.

The effort is backed by the X Prize Foundation, which successfully spurred on the first private spaceflight with the Ansari X Prize and has also launched the $30 million Google Lunar X Prize for teams racing to land a robot on the moon. Similarly, the $10 million Progressive Auto X Prize recently awarded money to the most fuel-efficient vehicles from among more than 100 competitors.

Now the X Prize Foundation hopes the lure of big rewards can attract more private money and talent to the effort of untangling the serious brain puzzles faced by modern-day researchers.

Securing a satellite for free Internet access

Kosta Grammatis doesn't see the Internet as a luxury as a human right for the billions of people who still lack access to one of the most powerful tools of the 21st century. That's why he launched a bid to buy a satellite and move it to a new orbit where it can provide free Internet access for one or more developing countries. His nonprofit organization, called A Human Right, is looking for $150,000 in donations through the online site buythissatellite.org so it can put together a business plan.

The target acquisition is the Terrestar-1 satellite, which is owned by a company that filed for bankruptcy protection in October. Grammatis hopes eventually to persuade a generous big spender such as Google or Richard Branson to back his bid for Terrestar-1, and then to re-park the satellite above a region with poor Internet access – perhaps above Papua New Guinea or even Africa.

To keep the operation funded, Grammatis envisions leasing out high-speed bandwidth to telecommunications companies, even while providing free Internet connections at lower speeds. If a serious project backer can be found, look for a possible move on this plan in 2011.

Declaring a fourth domain of life

In October, researchers announced the discovery of the world's second giant virus, dubbed CroV. This virus, which infects single-cell marine creatures, is considered enormous due to the size of its genome – approximately 730,000 base pairs, or genetic building blocks, more than double the size of the largest known "normal" virus. Mimivirus, the king of giant viruses so far, has 1.2 million base pairs.

More giant viruses are likely on their way to being found. Mimivirus and CroV are only distant relatives of each other, suggesting that others exist, according to Matthias Fischer who described CroV for his doctoral dissertation at the University of British Columbia. Gunnar Bratbak, of the University of Bergen in Norway, confirmed that his lab has isolated and is studying additional giant viruses.

Viruses, which rely on the machinery of infected cells to reproduce and so aren't considered "alive," are not included in the three domains of life: eukaryotes, prokaryotes and the most ancient, archaea. However, the surprising contents of these giant viruses' genomes endow them with features similar to cells and allow them to play a more active role in replicating themselves.

Research published Dec. 2 in the journal PLoS ONE reconstructs evolutionary relationships between the three domains and viruses, arguing that viruses are entitled to a domain for themselves. Viruses and all other organisms share a common set of genes involved in DNA processing, according to the researchers at Université de la Méditerranée in France.

Bratbak does not believe viruses are "alive" but that they are an important part of life and evolution, and excluding them from the domains is tricky, he told LiveScience in an e-mail.

"Viruses are not only a 'process' that aid evolution by shuffling genes around, but they are also evolving and obeying the same laws of evolution as the other domains," Bratbak wrote. "Thus the more we learn, the harder it gets to define 'domain' without including viruses among them. I am not sure we are there yet."

Confirming an Earth-like planet beyond the solar system

Plenty of claims have been made about finding what may be an Earth-like exoplanet – one that's rocky, about Earth’s size and orbiting its star within the habitable zone (where it's not too hot or too cold to sustain life as we know it).

"As regards 'definitively and positively identifying' a truly earth-like planet outside of our solar system, that all depends on what one means by definitively and positively," astronomer Steven Vogt of the University of California, Santa Cruz, told LiveScience in an e-mail.

"I would argue (and indeed have argued) that we have already done this, with the announced detection of GJ 581g," said Vogt, who led the team that found the planet.

Gliese 581g, one of six worlds orbiting a star in the constellation Libra, was announced as the first Earth-like planet where life might exist. While Vogt stands by the discovery, some science groups question the finding. For instance, a group of astronomers, led by Michel Mayor of the Geneva Observatory in Switzerland, performed a follow-up investigation in an attempt to confirm the existence of Gliese 581g and said they were unable to.

Even with Mayor's team and Vogt's team trying to confirm Gliese 581g, "it may take another season or two to really know, so I expect we won't see any possible confirmation (or refutation) for another year or two," Vogt said. "In the meantime, we are hard at work not only gathering more data on this system, but on others that may
yield similar potentially habitable planets."

The Kepler mission, which launched in spring 2009 and whose goal is to search for Earth-like worlds, hasn't been under way long enough to confirm habitable Earth-like exoplanets, Vogt said. Even so, MIT astrophysicist Sara Seager said she expects Kepler will making some amazing exoplanet discoveries in 2011, though likely not a truly Earth-like planet.

"To find a true Earth twin, we need to be able to find and characterize Earths orbiting true solar twins," Seager told LiveScience. "This isn't possible until we have the money to invest in a 'Terrestrial Planet Finder,' a direct imaging space telescope, one that is capable of blocking out the starlight to search for a planet that is 10 billion times fainter than its host star. I hope this year brings some breakthroughs in technology in this regard."

Gregory Laughlin of the University of California, Santa Cruz, and Samuel Arbesman, a computational biologist at Harvard Medical School, are more optimistic, and specific, though they are not referring to an "Earth twin," but instead a planet similar to Earth where there's a possibility of life.

"In the past decades, the number of known extrasolar planets has ballooned into the hundreds, and with it the expectation that the discovery of the first Earth-like extrasolar planet is not far off," they write in an online research article published on arXiv.org. Using statistical analyses based on past exoplanet discoveries, "we predict the discovery of the first Earth-like planet to be announced in the first half of 2011, with the likeliest date being early May 2011," they wrote.

More details on how they came to the conclusion can be found at Arbesman's blog.

Understanding what your genes do for you

The studies linking genes to behavior come fast and furious these days: Scientists have found a gene for impulsivity, for promiscuity, even for liberalism. And that's just in the last few months.

Of course, all these findings come with a huge disclaimer: Genes aren't destiny. A single gene won't make you prone to violence or sex, nor will it force you to vote for Barack Obama. On its own, the presence of one of these "behavior" gene variants tells you precisely nothing about the person carrying it.

So what's the point? It’s a growing understanding of the complex interactions between our genes and the environment, researchers say. New genome sequencing techniques allow researchers to cast wider and deeper nets in the search for genetic links to behavior. Close study can reveal how early-life experiences or exposure to certain situations can influence those genes. Even your parents' experiences could make a difference in how your genes are expressed.

It's the beginning of a new era, said David Goldman, a geneticist at the National Institute on Alcohol Abuse and Alcoholism, who authored the study on the genetics of impulsivity.

"To generate a million nucleotides of DNA sequence costs about 25 cents, which is just an astounding number," Goldman told LiveScience. "What else in life is that cheap?"

Don't expect a simple breakthrough in 2011 – it's highly unlikely that anyone is going to discover THE depression gene or THE schizophrenia gene. But psychiatry researchers say they're gradually piecing together the gene-environment puzzle, and new clues could arise any day.

"We really might identify new genes and new proteins that are involved in depression that we never thought to look at before," said Srijan Sen, a psychiatrist at the University of Michigan. "That's happening a little bit in schizophrenia and autism… In that way, I think revolutionary things could happen."

Dining on genetically modified salmon

A transgenic salmon that grows to meal size in half the time of ordinary salmon is poised to become the first genetically modified animal approved by the U.S. Food and Drug Administration for consumption. But despite a series of recent FDA panels finding that it does not pose any new threat to human health, the AquaBounty Technologies fish still faces criticism from experts and the threat of lawsuits from consumer organizations.

The panel hearings found the AquaBounty salmon to be safe, based on studies that some critics have argued involved too few fish; the FDA has not indicated whether it will require additional studies before ruling on the panels’ recommendation. The environmental risks of the transgenic salmon escaping their indoor facilities and mingling with wild salmon were also considered minimal.

Some economists have argued that the FDA also needs to consider how the AquaBounty salmon could encourage an expansion of the aquaculture industry that raises farm-bred fish. That move could make salmon cheaper and allow for a healthier diet among consumers on the plus side, but also may drain the numbers of wild fish required to feed the growing numbers of farm salmon.

Either way, the salmon will not represent the first genetically modified food to enter human diets if it gets FDA approval in 2011 – just look at the ingredients of your next package of corn chips.

Learning the cultures of Earth’s other creatures

Evidence of culture – learned behavior characteristics of a particular group – among animals is mounting, and research is continuing to add nuance to our understanding of how animals learn from one another and how animal culture, like human culture, evolves.

Within the next year, Diana Reiss of Hunter College in New York City, and collaborator Ofer Tchernichovski at the City College of New York plan to embark on research that could show, among other things, how dolphins learn new whistles – the sounds by which they communicate – and how they incorporate them into their own social interactions.

A new experimental system the two scientists are developing will allow a social group of dolphins at the National Aquarium in Baltimore to interact with a touch screen projected onto the wall of the tank, while identifying the whistles the animals make, in near-real time.

When asked if findings from animal culture mean humans are not unique in that regard, Tchernichovski balked, calling it a "trick question."

"The more interesting science is the science using animal models to understand ourselves and to understand animals and to see [if] there is a continuum between them," he told LiveScience.

Finding the causes of animal-disease epidemics

In recent years, colony collapse disorder has emptied out honeybee colonies in North America and Europe, and chytrid fungal infections are blamed for amphibian deaths and declining populations on several continents. Most recently, white-nose syndrome has been decimating hibernating bats as it radiates outward from a cave near Albany, N.Y., where it was first seen February 2006.

Scientists are piecing together the causes for these animal plagues, though many questions remain. In October, researchers reported in the journal PLoS ONE that a viral-fungal tag team was likely behind colony collapse, becoming more lethal when the virus and fungus infected the same bee together.

As for the skin infection causing amphibian deaths, a study published in the journal Science in 2009 proposed that the infectious disease, chytridimycosis, interferes with electrolyte transport over the skin, causing cardiac arrest and death. Separately, researchers have suggested that the fungus responsible was transported around the globe by the trade in African frogs, which were used in pregnancy tests during the first part of the 20th century.

The fungus behind white-nose syndrome may use a similar mechanism to kill bats, according to a study published in November in the journal BMC Biology. "In the next few years, it's plausible we will be able to establish exactly how the fungus is killing the bats, and that knowledge may certainly help us come up with the most effective management options," said Paul Cryan, a study researcher and bat ecologist with the U.S. Geological Survey.

Top 10 scientific discoveries in 2010

2011-10-18T05:10:00.001-07:00

The year of 2010 is full of excitement as the world has witnessed many technological wonders and scientific breakthroughs.Below are the top 10 scientific discoveries of the year.
Top 1: Creation of first self-replicating synthetic life

The Presidential Commission for the Study of Bioethical Issues has called for enhanced federal oversight in the emerging field of synthetic biology, which involves the design and construction of laboratory-made biological parts.

In May, researchers from the J. Craig Venter Institute (JCVI), a not-for-profit, genomic-focused basic research organization, reported the successful construction of a first self-replicating, synthetic bacterial cell. They copied and modified an entire genome of a small bacterial cell, inserted it into a living cell of another species, and by doing so created a new, synthetic organism.

"This is the first self-replicating species that we've had on the planet whose parent is a computer," U.S. scientist Craig Venter who led the team said. "It also is the first species to have its own website encoded in its genetic code."
Scientists hope to patent the organism called Mycoplasma laboratorium and engineer it to manufacture cheap biofuels, medicines and other useful compounds.
However, critics argue the move will stifle future science relying on an artificial microbes. U.S. President Obama has asked the Presidential Commission for the Study of Bioethical Issues to study the implications of synthetic biology after proponent, however, no federal regulations has been issued yet.
Top 2: Scientists found life built with toxic chemical

transmission electron micrograph of the bacterium strain GFAJ-1+As/-P GFAJ-1 shows internal vacuole-like structures in an undated photograph released by NASA, the journal Science and the American Association for the Advancement of Science on December 2, 2010. A strange, salty lake in California has yielded the equally strange bacterium that thrives on arsenic and redefines life as we know it, researchers reported on Thursday. The finding shows just how little scientists know about the variety of life forms on Earth, and may greatly expand where they should be looking for life on other planets and moons, the NASA-funded team said.

An astrobiology research has found the first known microorganism able to thrive and reproduce using the toxic chemical arsenic, which has changed the fundamental knowledge about what comprises all known life on Earth.
This finding of an alternative biochemistry makeup will alter biology textbooks and expand the scope of the search for life beyond Earth. The research is published in this week's edition of Science Express.
Phosphorus is a central component of the energy-carrying molecule in all cells (adenosine triphosphate) and also the phospholipids that form all cell membranes. Arsenic, which is chemically similar to phosphorus, is poisonous for most life on Earth. Arsenic disrupts metabolic pathways because chemically it behaves similarly to phosphate.
Top 3: Antimatter made & trapped in lab for the first time

In Dan Brown's Angels & Demons book, scientists have solved one of the most complicated scientific problems: the capture and storage of antimatter. In the real life, capturing atomic antimatter is yet to be achieved.

Antimatter Have you read Dan Brown's Angels & Demons book or watched the movie, in which symbologist Robert Langdon tries to stop a legendary secret society Illuminati from destroying Vatican City with the newly discovered power of antimatter stored in a canister?
According to the book, antimatter is an extremely dangerous substance with immense destructive potential, which is unleashed upon contact with any form of normal matter, and is comparable to a small nuclear weapon. In the story, scientists have solved one of the most complicated scientific problems: the capture and storage of antimatter.
Now the story is coming true in real life as researchers at CERN's Geneva labs have recently managed to trap a sizeable amount of antihydrogenhave managed to trap a sizeable amount of antihydrogen.
The development opens the path to new ways of making detailed measurements of antihydrogen. This will in turn allow scientists to compare matter and antimatter, which remains one of the biggest mysteries of science.
Top 4: Scientists Solve Mystery Of Mass In Variable Stars

Astronomers have found the first double star in which a pulsating variable and another star pass in front of one another, solving a a decades-old mystery in the process.
"By using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, along with other telescopes, we have measured the mass of a Cepheid with an accuracy far greater than any earlier estimates," said Grzegorz Pietrzyski, of the Universidad de Concepción in Chile and the Warsaw University Observatory in Poland. "This new result allows us to immediately see which of the two competing theories predicting the masses of Cepheids is correct."
Top 5: Astronomers Discover 'Rosetta Stone' For T-dwarf Stars

An international team of astronomers has discovered a unique star system comprised of a very cool, methane-rich dwarf star and a white dwarf star in orbit around each other, the the European Southern Observatory (ESO) said on November 22.
The system, which is the first of its type to be found, is a "Rosetta Stone" for such dwarf stars and gives scientists a way of finding the mass and age of the methane dwarf, known as a T-dwarf star.
Top 6: Mysterious Giant bubbles discovered in Milky Way

Scientists have discovered two massive gamma-ray emitting bubbles in the center of Milky Way galaxy.
Astronomers say the bubbles, which may be millions of years old, span more than half of the visible sky, from the constellation Virgo to the constellation Grus.
Scientists are now conducting more analyses to better understand the nature those bubbles, which appear to have well-defined edges and emit high energy gamma-ray fog not seen elsewhere in the Milky Way.
Scientists believe that the bubbles could have been formed as a result of gas outflows from a burst of star formation, perhaps the one that produced many massive star clusters in the Milky Way's center several million years ago.
Top 7: Possible Ice Volcanoes Spotted On Moon Of Saturn

Scientists have found possible ice volcanoes on Saturn's moon Titan, similar to those on Earth that spew molten rock.
Topography and surface composition data from NASA's Cassini Spacecraft have enabled scientists to make the best case yet for an Earth-like volcanic landform that erupts with ice instead of lava.
Titan is the largest moon of Saturn and the only natural satellite known to have a dense atmosphere. Titan is also the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found.
Top 8: Wobble May Keep Water Liquid On Moon Of Saturn

The surface of Saturn's moon Enceladus averages a very cold -198 degrees Celsius, which is enough to keep nitrogen liquid. So there shouldn't be any liquid water.
But that view changed when in 2005 the Cassini spacecraft got a picture of a plume of water rising from the surface. Recently scientists at the National Aeronautics and Space Administration have theorized that Enceladus rotates unevenly, giving rise to tidal forces that create heat, which keeps the water below the surface liquid.
Astronomers discover another Earth-like planet outside solar system.
Astronomers have discovered a habitable rocky planet in another solar system for the first time that could be another Earth-like discovery with basic and essential conditions needed to support extraterrestrial life after a decade long hunt ending human race's cosmic loneliness.
They said life does not necessarily exist on the planet but that the basic conditions are present to allow it to begin and keep it going. According to them, the planet is large enough to have the gravitational force to hold an atmosphere surrounding it and data tell scientists that any water on the new planet will be in liquid form.
However, scientists say there is no evidence that Gliese 581G holds oxygenated landscapes of green and blue that would support microbes, dinosaurs or some alien-looking pre-human. For life, there must be water, and there's no proof of that as yet.
Top 9: Planetary collisons in double star-systems leave no room for life to emerge

Since double star-systems make planets collide, any chances of life emerging on these planets is impossible, says a NASA report.
"This is real-life science fiction," said Jeremy Drake of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass said in news release from NASA's Jet Propulsion Laboratory. "Our data tells us that planets in these systems might not be so lucky -- collisions could be common. It's theoretically possible that habitable planets could exist around these types of stars, so if there happened to be any life there, it could be doomed."
Top 10: Super-volcano erupts in outer galaxy, similar to Icelandic volcano on Earth

A galactic super-volcano is erupting in massive galaxy M87 and blasting gas outwards, and NASA scientists view that the huge volcano in M87 is very similar to the recent Icelandic volcano that caused heavy air traffic disruptions across Europe.
According to NASA's Chandra X-ray Observatory, M87 is relatively close to the Earth at a distance of about 50 million light years and lies at the center of the Virgo cluster, which contains thousands of galaxies.
Signs of life on Titan?
An analysis of data from NASA's Cassini probe shows depletions of certain chemicals on the surface. Back in 2005, Chris McKay, an astrobiologist at NASA, said one line of evidence for life would be unusual depletions of acetylene, ethane and hydrogen at the surface.
While the findings aren't conclusive, some suggest the hydrogen and acetylene could be disappearing because they are being used by methane-based life in the same way life on Earth uses oxygen and other chemicals.

Food technology

2011-10-13T04:28:00.000-07:00

Food technology, or food tech for short is the application of food science to the selection, preservation, processing, packaging, distribution, and use of safe, nutritious, and wholesome food.
Food scientists and food technologists study the physical, microbiological, and chemical makeup of food. Depending on their area of specialization, food scientists may develop ways to process, preserve, package, or store food, according to industry and government specifications and regulations. Consumers seldom think of the vast array of foods and the research and development that has resulted in the means to deliver tasty, nutritious, safe, and convenient foods.

Early history of food technology

Research in the field now known as food technology has been conducted for decades. Nicolas Appert’s development in 1810 of the canning process was a decisive event. The process wasn’t called canning then and Appert did not really know the principle on which his process worked, but canning has had a major impact on food preservation techniques.

Louis Pasteur's research on the spoilage of wine and his description of how to avoid spoilage in 1864 was an early attempt to put food technology on a scientific basis. Besides research into wine spoilage, Pasteur did research on the production of alcohol, vinegar, wines and beer, and the souring of milk. He developed pasteurization—the process of heating milk and milk products to destroy food spoilage and disease-producing organisms. In his research into food technology, Pasteur became the pioneer into bacteriology and of modern preventive medicine.

By the 1940s to 1950s, the original four departments that had taught the subject under different names in the US (including those at the University of Massachusetts and the University of California) had been retitled "food science", "food science and technology", or a similar variant.

Food packaging

2011-10-13T04:26:00.000-07:00

Food packaging is packaging for food. It requires protection, tampering resistance, and special physical, chemical, or biological needs. It also shows the product that is labeled to show any nutrition information on the food being consumed.

Functions of food packaging

Packaging has several objectives

    Physical protection - The food enclosed in the package may require protection from, among other things, shock, vibration, compression, temperature, etc.
    Barrier protection - A barrier from oxygen, water vapor, dust, etc., is often required. Permeation is a critical factor in design. Some packages contain desiccants or Oxygen absorbers to help extend shelf life. Modified atmospheres or controlled atmospheres are also maintained in some food packages. Keeping the contents clean, fresh, and safe for the intended shelf life is a primary function.
    Containment or agglomeration - Small items are typically grouped together in one package for reasons of efficiency. powders, and granular materials need containment.
    Information transmission - Packages and labels communicate how to use, transport, recycle, or dispose of the package or product. Some types of information are required by governments.
    Marketing - The packaging and labels can be used by marketers to encourage potential buyers to purchase the product. Package design has been an important and constantly evolving phenomenon for several decades. Marketing communications and graphic design are applied to the surface of the package and (in many cases) the point of sale display.
    Security - Packaging can play an important role in reducing the security risks of shipment. Packages can be made with improved tamper resistance to deter tampering and also can have tamper-evident features to help indicate tampering. Packages can be engineered to help reduce the risks of package pilferage: Some package constructions are more resistant to pilferage and some have pilfer indicating seals. Packages may include authentication seals to help indicate that the package and contents are not counterfeit. Packages also can include anti-theft devices, such as dye-packs, RFID tags, or electronic article surveillance tags, that can be activated or detected by devices at exit points and require specialized tools to deactivate. Using packaging in this way is a means of retail loss prevention.
    Convenience - Packages can have features which add convenience in distribution, handling, stacking, display, sale, opening, reclosing, use, and reuse.
    Portion control - Single serving packaging has a precise amount of contents to control usage. Bulk commodities (such as salt) can be divided into packages that are a more suitable size for individual households. It also aids the control of inventory: selling sealed one-liter-bottles of milk, rather than having people bring their own bottles to fill themselves.

Food chemistry

2011-10-13T04:24:00.001-07:00

Food chemistry is the study of chemical processes and interactions of all biological and non-biological components of foods. The biological substances include such items as meat, poultry, lettuce, beer, and milk as examples. It is similar to biochemistry in its main components such as carbohydrates, lipids, and protein, but it also includes areas such as water, vitamins, minerals, enzymes, food additives, flavors, and colors. This discipline also encompasses how products change under certain food processing techniques and ways either to enhance or to prevent them from happening. An example of enhancing a process would be to encourage fermentation of dairy products with microorganisms that convert lactose to lactic acid; an example of preventing a process would be stopping the browning on the surface of freshly cut Red Delicious apples using lemon juice or other acidulated water.

Food engineering

2011-10-13T04:23:00.000-07:00

Food engineering is a multidisciplinary field of applied physical sciences which combines science, microbiology, and engineering education for food and related industries. Food engineering includes, but is not limited to, the application of agricultural engineering, mechanical engineering and chemical engineering principles to food materials. Food engineers provide the technological knowledge transfer essential to the cost-effective production and commercialization of food products and services.
Food engineering is a very wide field of activities. Prospective major employers for food engineers include companies involved in food processing, food machinery, packaging, ingredient manufacturing, instrumentation, and control. Firms that design and build food processing plants, consulting firms, government agencies, pharmaceutical companies, and health-care firms also hire food engineers. Among its domain of knowledge and action are:

research and development of new foods, biological and pharmaceutical products
development and operation of manufacturing, packaging and distributing systems for drug/food products
design and installation of food/biological/pharmaceutical production processes
design and operation of environmentally responsible waste treatment systems
marketing and technical support for manufacturing plants.

Topics in food engineering

In the development of food engineering, one of the many challenges is to employ modern tools and knowledge, such as computational materials science and nanotechnology, to develop new products and processes. Simultaneously, improving quality, safety, and security remain critical issues in food engineering study. New packaging materials and techniques are being developed to provide more protection to foods, and novel preservation technologies are emerging. Additionally, process control and automation regularly appear among the top priorities identified in food engineering. Advanced monitoring and control systems are developed to facilitate automation and flexible food manufacturing. Furthermore, energy saving and minimization of environmental problems continue to be important food engineering issues, and significant progress is being made in waste management, efficient utilization of energy, and reduction of effluents and emissions in food production.
Typical topics include:

Advances in classical unit operations in engineering applied to food manufacturing
Progresses in the transport and storage of liquid and solid foods
Developments in heating, chilling and freezing of foods
Advanced mass transfer in foods
New chemical and biochemical aspects of food engineering and the use of kinetic analysis
New techniques in dehydration, thermal processing, non-thermal processing, extrusion, liquid food concentration, membrane processes and applications of membranes in food processing
Shelf-life, electronic indicators in inventory management, and sustainable technologies in food processing
Modern packaging, cleaning, and sanitation technologies

Food preservation

2011-10-13T04:22:00.000-07:00

Food preservation is the process of treating and handling food to stop or slow down spoilage (loss of quality, edibility or nutritional value) and thus allow for longer storage.
Preservation usually involves preventing the growth of bacteria, yeasts, fungi, and other micro-organisms (although some methods work by introducing benign bacteria, or fungi to the food), as well as retarding the oxidation of fats which cause rancidity. Food preservation can also include processes which inhibit visual deterioration that can occur during food preparation; such as the enzymatic browning reaction in apples after they are cut.
Many processes designed to preserve food will involve a number of food preservation methods. Preserving fruit, by turning it into jam, for example, involves boiling (to reduce the fruit’s moisture content and to kill bacteria, yeasts, etc.), sugaring (to prevent their re-growth) and sealing within an airtight jar (to prevent recontamination). There are many traditional methods of preserving food that limit the energy inputs and reduce carbon footprint.
Maintaining or creating nutritional value, texture and flavour is an important aspect of food preservation, although, historically, some methods drastically altered the character of the food being preserved. In many cases these changes have now come to be seen as desirable qualities – cheese, yoghurt and pickled onions being common examples.

Preservation processes

Preservation processes include

Heating to kill or denature micro-organisms (e.g., boiling)
Oxidation (e.g., use of sulfur dioxide)
Ozonation (e.g., use of ozone [O3] or ozonated water to kill undesired microbes)
Toxic inhibition (e.g., smoking, use of carbon dioxide, vinegar, alcohol etc.)
Dehydration (drying)
Osmotic inhibition (e.g., use of syrups)
Low temperature inactivation (e.g., freezing)
Ultra high water pressure (e.g. a type of “cold” pasteurization; intense water pressure kills microbes which cause food deterioration and affect food safety)

Food microbiology

2011-10-13T04:20:00.000-07:00

Food microbiology is the study of the microorganisms that inhabit, create, or contaminate food. Of major importance is the study of microorganisms causing food spoilage. "Good" bacteria, however, such as probiotics, are becoming increasingly important in food science. In addition, microorganisms are essential for the production of foods such as cheese, yogurt, other fermented foods, bread, beer and wine.

Food safety

Food safety is a major focus of food microbiology. Pathogenic bacteria, viruses and toxins produced by microorganisms are all possible contaminants of food. However, microorganisms and their products can also be used to combat these pathogenic microbes. Probiotic bacteria, including those that produce bacteriocins, can kill and inhibit pathogens. Alternatively, purified bacteriocins such as nisin can be added directly to food products. Finally, bacteriophages, viruses that only infect bacteria, can be used to kill bacterial pathogens. Thorough preparation of food, including proper cooking, eliminates most bacteria and viruses. However, toxins produced by contaminants may not be heat-labile, and some are not eliminated by cooking. ...

Fermentation

Fermentation is one way microorganisms can change a food. Yeast, especially Saccharomyces cerevisiae, is used to leaven bread, brew beer and make wine. Certain bacteria, including lactic acid bacteria, are used to make yogurt, cheese, hot sauce, pickles, fermented sausages and dishes such as kimchi. A common effect of these fermentations is that the food product is less hospitable to other microorganisms, including pathogens and spoilage-causing microorganisms, thus extending the food's shelf-life.
Food fermentations are ancient technologies that harness microorganisms and their enzymes to improve the human diet. Fermented foods keep better, have enhanced flavours, textures and aromas, and may also possess certain health benefits, including superior digestibility. For vegetarians, fermented foods serve as palatable, protein-rich meat substitutes.
Some cheese varieties also require molds to ripen and develop their characteristic flavors.
Asian cuisines rely on a large repertoire of fermented foods. In particular, Aspergillus oryzae and A. sojae, sometimes called koji molds, are employed in many ways. Their hydrolytic enzymes suit them for growth on starch and other carbohydrate-rich substrates. In the koji process, fungal enzymes perform the same function as the malting enzymes used in the beer fermentations of western cultures. The koji molds release amylases that break down rice starch, which in turn can be fermented to make rice wine. Fermented rice beverages have numerous local variations and names, depending on country and region. Rice wine is called shaoshing in parts of China, sake in Japan, takj or yakju in Korea, as well as by many other names across Asia. The koji molds are also effective in a variety of legume fermentations, of which miso and soy sauce are best known. Miso is a mixture of soybeans and cereals usually used to flavour soups. Soy sauce is a flavourful, salty liquid sauce made from soybeans that have been fermented by koji molds, yeasts, as well as several halophilic bacteria. Other names for soy sauce include jiangyou (China), makjang and kanjang (Korea), toyo (Philippines) and siiu (Thailand)^.

Probiotics

Probiotics are living organisms that, when consumed, have beneficial health benefits outside their inherent nutritional effects. There is a growing body of evidence for the role of probiotics in gastrointestinal infections, irritable bowel syndrome and inflammatory bowel disease
Lactobacillus species are used for the production of yogurt, cheese, sauerkraut, pickles, beer, wine, cider, kimchi, chocolate and other fermented foods, as well as animal feeds such as silage. In recent years, much interest has been shown in the use of lactobacilli as probiotic organisms and their potential for disease prevention in humans and animals.
Bifidobacteria are considered as important probiotics, and are used in the food industry to relieve and treat many intestinal disorders. Bifidobacteria exert a range of beneficial health effects, including the regulation of intestinal microbial homeostasis, the inhibition of pathogens and harmful bacteria that colonize and/or infect the gut mucosa, the modulation of local and systemic immune responses, the repression of procarcinogenic enzymatic activities within the microbiota, the production of vitamins, and the bioconversion of a number of dietary compounds into bioactive molecules.

Food safety

2011-10-13T04:17:00.000-07:00

Food safety is a scientific discipline describing handling, preparation, and storage of food in ways that prevent foodborne illness. This includes a number of routines that should be followed to avoid potentially severe health hazards. Food can transmit disease from person to person as well as serve as a growth medium for bacteria that can cause food poisoning. Debates on genetic food safety include such issues as impact of genetically modified food on health of further generations and genetic pollution of environment, which can destroy natural biological diversity. In developed countries there are intricate standards for food preparation, whereas in lesser developed countries the main issue is simply the availability of adequate safe water, which is usually a critical item. In theory food poisoning is 100% preventable.

Key principles

Five key principles

The five key principles of food hygiene, according to WHO, are:

Prevent contaminating food with pathogens spreading from people, pets, and pests.
Separate raw and cooked foods to prevent contaminating the cooked foods.
Cook foods for the appropriate length of time and at the appropriate temperature to kill pathogens.
Store food at the proper temperature.
Use safe water and raw materials

ISO 22000

ISO 22000 is a standard developed by the International Organization for Standardization dealing with food safety. This is a general derivative of ISO 9000. ISO 22000 standard: The ISO 22000 international standard specifies the requirements for a food safety management system that involves interactive communication, system management, prerequisite programs, HACCP principles.

Incidence

A 2003 World Health Organization (WHO) report concluded that about 40% of reported food poisoning outbreaks in the WHO European Region occur in private homes. According to the WHO and CDC, in the USA alone, annually, there are 76 million cases of foodborne illness leading to 325,000 hospitalizations and 5,000 deaths.

Food science

2011-10-13T04:14:00.001-07:00

Food science is a study concerned with all technical aspects of foods, beginning with harvesting or slaughtering, and ending with its cooking and consumption, an ideology commonly referred to as "from field to fork". It is considered one of the life sciences and is usually considered distinct from the field of nutrition.

What is technology ?

2011-10-10T06:18:00.000-07:00

Technology is the making, usage, and knowledge of tools, machines, techniques, crafts, systems or methods of organization in order to solve a problem or perform a specific function. It can also refer to the collection of such tools, machinery, and procedures. The word technology comes from Greek τεχνολογία (technología); from τέχνη (téchnē), meaning "art, skill, craft", and -λογία (-logía), meaning "study of-". The term can either be applied generally or to specific areas: examples include construction technology, medical technology, and information technology.

Technologies significantly affect human as well as other animal species' ability to control and adapt to their natural environments. The human species' use of technology began with the conversion of natural resources into simple tools. The prehistorical discovery of the ability to control fire increased the available sources of food and the invention of the wheel helped humans in travelling in and controlling their environment. Recent technological developments, including the printing press, the telephone, and the Internet, have lessened physical barriers to communication and allowed humans to interact freely on a global scale. However, not all technology has been used for peaceful purposes; the development of weapons of ever-increasing destructive power has progressed throughout history, from clubs to nuclear weapons.

Technology has affected society and its surroundings in a number of ways. In many societies, technology has helped develop more advanced economies (including today's global economy) and has allowed the rise of a leisure class. Many technological processes produce unwanted by-products, known as pollution, and deplete natural resources, to the detriment of the Earth and its environment. Various implementations of technology influence the values of a society and new technology often raises new ethical questions. Examples include the rise of the notion of efficiency in terms of human productivity, a term originally applied only to machines, and the challenge of traditional norms.

Philosophical debates have arisen over the present and future use of technology in society, with disagreements over whether technology improves the human condition or worsens it. Neo-Luddism, anarcho-primitivism, and similar movements criticise the pervasiveness of technology in the modern world, opining that it harms the environment and alienates people; proponents of ideologies such as transhumanism and techno-progressivism view continued technological progress as beneficial to society and the human condition. Indeed, until recently, it was believed that the development of technology was restricted only to human beings, but recent scientific studies indicate that other primates and certain dolphin communities have developed simple tools and learned to pass their knowledge to other generations.

How science changed our world

2011-10-10T06:16:00.000-07:00

http://www.youtube.com/watch?v=3oH6apmb6sY

A good video to get the exact view over science and tech how it changed and also changed our world...............

Sahara fish discovery enforces Out-of-Africa theory

2011-10-10T06:13:00.001-07:00

Fish may have once swum across the Sahara, a finding that could shed light on how humanity made its way out of Africa, researchers said. The cradle of humanity lies south of the Sahara, which begs the question as to how our species made its way past it. The Sahara is the largest hot desert in the world, and would seem a major barrier for any humans striving to migrate off the continent.
Scientists have often focused on the Nile Valley as the corridor by which humans left Africa. However, considerable research efforts have failed to uncover evidence for its consistent use by people leaving the continent, and precisely how watery it has been over time is controversial.
Now it turns out the Sahara might not have been quite as impassable as once thought — not only for humanity, but for fish as well.
"Fish appeared to have swam across the Sahara during its last wet phase sometime between 10,000 and 6,000 years ago," researcher Nick Drake, a geographer at King's College London, told LiveScience. "The Sahara is not a barrier to the migrations of animals and people. Thus it is possible — likely? —that early modern humans did so, and this could explain how we got out of Africa."
Using satellite imagery and digital maps of the landscape, the researchers found the Sahara was once covered by a dense network of rivers, lakes and inland deltas. This large waterway channeled water and animals into and across the Sahara during wet, "green" times.
In their analysis, Drake and his colleagues found evidence that many creatures, including aquatic ones, dispersed across the Sahara recently. For example, 25 North African animal species have populations both north and south of the Sahara with small refuges within the desert, including catfish (Clarias gariepinus), tilapia (Tilapia zillii), jewel cichlid fish (Hemichromis letourneuxi) and freshwater snails such as the red-rimmed melania (Melanoides tuberculata). Indeed, more animals may have once crossed over the Sahara than over the Nile corridor, the researchers said — only nine animal species that occupy the Nile corridor today are also found both north and south of the Sahara.
If fish could have crossed the Sahara, it is hard to imagine that humans didn't. Analysis of African languages and artifacts suggest that ancient waterways recently affected how humans occupied the Sahara. For instance, speakers of Nilo-Saharan languages once lived across central and southern Sahara, and may have once hunted aquatic creatures with barbed bone points and fish hooks. In addition, ancient lake sediments suggest the Sahara was green roughly 125,000 years ago, back when anatomically modern humans might have begun migrating out of Africa.
Future work could focus on when species got across the Sahara — genetic analysis of fish could help pinpoint such times in fish, Drake said. However, further research into the past of the Sahara could prove difficult and even dangerous, he noted. Some of the Saharan countries the researchers would like to visit in order to analyze the genetics of fish populations or date the ages of ancient shorelines "are deemed to be too dangerous to visit due to terrorist activity or civil war," Drake said.
The scientists detailed their findings online Dec. 27 in the journal Proceedings of the National Academy of Sciences.

The Scientific 100: A Ranking of the Most Influential Scientists, Past and Present

2011-10-07T03:38:00.000-07:00

1     Isaac Newton     the Newtonian Revolution     Anglican (rejected Trinitarianism, i.e., Athanasianism;
                                                                              believed in the Arianism of the Primitive Church)
2     Albert Einstein     Twentieth-Century Science     Jewish
3     Neils Bohr       the Atom     Jewish Lutheran
4     Charles Darwin     Evolution     Anglican (nominal); Unitarian
5     Louis Pasteur    the Germ Theory of Disease     Catholic
6     Sigmund Freud    Psychology of the Unconscious     Jewish; Atheist; Freudian psychoanalysis (Freudianism)
7     Galileo Galilei the New Science     Catholic
8     Antoine Laurent Lavoisier      the Revolution in Chemistry     Catholic
9     Johannes Kepler     Motion of the Planets     Lutheran
10     Nicolaus Copernicus     the Heliocentric Universe     Catholic (priest)
11     Michael Faraday     the Classical Field Theory     Sandemanian
12     James Clerk Maxwell     the Electromagnetic Field     Presbyterian; Anglican; Baptist
13     Claude Bernard     the Founding of Modern Physiology
14     Franz Boas     Modern Anthropology     Jewish
15     Werner Heisenberg     Quantum Theory     Lutheran
16     Linus Pauling     Twentieth-Century Chemistry     Lutheran
17     Rudolf Virchow     the Cell Doctrine
18     Erwin Schrodinger     Wave Mechanics     Catholic
19     Ernest Rutherford     the Structure of the Atom
20     Paul Dirac     Quantum Electrodynamics
21     Andreas Vesalius     the New Anatomy     Catholic
22     Tycho Brahe     the New Astronomy     Lutheran
23     Comte de Buffon     l'Histoire Naturelle
24     Ludwig Boltzmann     Thermodynamics
25     Max Planck     the Quanta     Protestant
26     Marie Curie     Radioactivity     Catholic (lapsed)
27     William Herschel     the Discovery of the Heavens     Jewish
28     Charles Lyell     Modern Geology
29     Pierre Simon de Laplace     Newtonian Mechanics     atheist
30     Edwin Hubble     the Modern Telescope
31     Joseph J. Thomson     the Discovery of the Electron
32     Max Born     Quantum Mechanics     Jewish Lutheran
33     Francis Crick     Molecular Biology     atheist
34     Enrico Fermi     Atomic Physics     Catholic
35     Leonard Euler     Eighteenth-Century Mathematics     Calvinist
36     Justus Liebig     Nineteenth-Century Chemistry
37     Arthur Eddington     Modern Astronomy     Quaker
38     William Harvey     Circulation of the Blood     Anglican (nominal)
39     Marcello Malpighi     Microscopic Anatomy     Catholic
40     Christiaan Huygens     the Wave Theory of Light     Calvinist
41     Carl Gauss (Karl Friedrich Gauss)     Mathematical Genius     Lutheran
42     Albrecht von Haller     Eighteenth-Century Medicine
43     August Kekule     Chemical Structure
44     Robert Koch     Bacteriology
45     Murray Gell-Mann     the Eightfold Way     Jewish
46     Emil Fischer     Organic Chemistry
47     Dmitri Mendeleev     the Periodic Table of Elements
48     Sheldon Glashow     the Discovery of Charm     Jewish
49     James Watson     the Structure of DNA     atheist
50     John Bardeen     Superconductivity
51     John von Neumann     the Modern Computer     Jewish Catholic
52     Richard Feynman     Quantum Electrodynamics     Jewish
53     Alfred Wegener     Continental Drift
54     Stephen Hawking     Quantum Cosmology     atheist
55     Anton van Leeuwenhoek     the Simple Microscope     Dutch Reformed
56     Max von Laue     X-ray Crystallography
57     Gustav Kirchhoff     Spectroscopy
58     Hans Bethe     the Energy of the Sun     Jewish
59     Euclid     the Foundations of Mathematics     Platonism / Greek philosophy
60     Gregor Mendel     the Laws of Inheritance     Catholic (Augustinian monk)
61     Heike Kamerlingh Onnes     Superconductivity
62     Thomas Hunt Morgan     the Chromosomal Theory of Heredity
63     Hermann von Helmholtz     the Rise of German Science
64     Paul Ehrlich     Chemotherapy     Jewish
65     Ernst Mayr     Evolutionary Theory     atheist
66     Charles Sherrington     Neurophysiology
67     Theodosius Dobzhansky     the Modern Synthesis     Russian Orthodox
68     Max Delbruck     the Bacteriophage
69     Jean Baptiste Lamarck     the Foundations of Biology
70     William Bayliss     Modern Physiology
71     Noam Chomsky     Twentieth-Century Linguistics     Jewish atheist
72     Frederick Sanger     the Genetic Code
73     Lucretius     Scientific Thinking     Epicurean; atheist
74     John Dalton     the Theory of the Atom     Quaker
75     Louis Victor de Broglie     Wave/Particle Duality
76     Carl Linnaeus     the Binomial Nomenclature     Christianity
77     Jean Piaget     Child Development
78     George Gaylord Simpson     the Tempo of Evolution
79     Claude Levi-Strauss     Structural Anthropology     Jewish
80     Lynn Margulis     Symbiosis Theory     Jewish
81     Karl Landsteiner     the Blood Groups     Jewish
82     Konrad Lorenz     Ethology
83     Edward O. Wilson     Sociobiology
84     Frederick Gowland Hopkins     Vitamins
85     Gertrude Belle Elion     Pharmacology
86     Hans Selye     the Stress Concept
87     J. Robert Oppenheimer     the Atomic Era     Jewish
88     Edward Teller     the Bomb     Jewish
89     Willard Libby     Radioactive Dating
90     Ernst Haeckel     the Biogenetic Principle
91     Jonas Salk     Vaccination     Jewish
92     Emil Kraepelin     Twentieth-Century Psychiatry
93     Trofim Lysenko     Soviet Genetics     Russian Orthodox; Communist
94     Francis Galton     Eugenics
95     Alfred Binet     the I.Q. Test
96     Alfred Kinsey     Human Sexuality     atheist
97     Alexander Fleming     Penicillin     Catholic
98     B. F. Skinner     Behaviorism     atheist
99     Wilhelm Wundt     the Founding of Psychology     atheist
100     Archimedes     the Beginning of Science     Greek philosophy

Theory of relativity

2011-10-07T03:32:00.000-07:00

The theory of relativity, or simply relativity, encompasses two theories of Albert Einstein: special relativity and general relativity. However, the word relativity is sometimes used in reference to Galilean invariance.
The term "theory of relativity" was based on the expression "relative theory" used by Max Planck in 1906, who emphasized how the theory uses the principle of relativity. In the discussion section of the same paper Alfred Bucherer used for the first time the expression "theory of relativity"
In September 2011, CERN found possible evidence of the theory being violated by particles travelling faster than light -- these results are currently being analyzed for accuracy.

Scope

The theory of relativity enriched physics and astronomy during the 20th century. When first published, relativity superseded a 200-year-old theory of mechanics elucidated by Isaac Newton. It changed perceptions. However, Einstein denied that Newton could ever be superseded by his own work.

The theory of relativity overturned the concept of motion from Newton's day, into all motion is relative. Time was no longer uniform and absolute. Therefore, no longer could physics be understood as space by itself, and time by itself. Instead, an added dimension had to be taken into account with curved spacetime. Time now depended on velocity, and contraction became a fundamental consequence at appropriate speeds.

In the field of physics, relativity catalyzed and added an essential depth of knowledge to the science of elementary particles and their fundamental interactions, along with ushering in the nuclear age. With relativity, cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes, and gravitational waves.

Two theory view

The theory of relativity was representative of more than a single new physical theory. It affected the theories and methodologies across all the physical sciences. However, as stated above, this is more likely perceived as two separate theories. There are some explanations for this. First, special relativity was published in 1905, and the final form of general relativity was published in 1916.

Second, special relativity fits with and solves for elementary particles and their interactions, whereas general relativity solves for the cosmological and astrophysical realm (including astronomy).

Third, special relativity was widely accepted in the physics community by 1920. This theory rapidly became a significant and necessary tool for theorists and experimentalists in the new fields of atomic physics, nuclear physics, and quantum mechanics. Conversely, general relativity did not appear to be as useful. There appeared to be little applicability for experimentalists as most applications were for astronomical scales. It seemed limited to only making minor corrections to predictions of Newtonian gravitation theory. Its impact was not apparent until the 1930s.

Finally, the mathematics of general relativity appeared to be incomprehensibly dense. Consequently, only a small number of people in the world, at that time, could fully understand the theory in detail. This remained the case for the next 40 years. Then, at around 1960 a critical resurgence in interest occurred which has resulted in making general relativity central to physics and astronomy. New mathematical techniques applicable to the study of general relativity substantially streamlined calculations. From this physically discernible concepts were isolated from the mathematical complexity. Also, the discovery of exotic astronomical phenomena in which general relativity was crucially relevant, helped to catalyze this resurgence. The astronomical phenomena included quasars (1963), the 3-kelvin microwave background radiation (1965), pulsars (1967), and the discovery of the first black hole candidates (1971)

On the theory of relativity

Einstein stated that the theory of relativity belongs to the class of "principle-theories". As such it employs an analytic method. This means that the elements which comprise this theory are not based on hypothesis but on empirical discovery. The empirical discovery leads to understanding the general characteristics of natural processes. Mathematical models are then developed which separate the natural processes into theoretical-mathematical descriptions. Therefore, by analytical means the necessary conditions that have to be satisfied are deduced. Separate events must satisfy these conditions. Experience should then match the conclusions.
The special theory of relativity and the general theory of relativity are connected. As stated below, special theory of relativity applies to all inertial physical phenomena except gravity. The general theory provides the law of gravitation, and its relation to other forces of nature.

Special relativity

USSR stamp dedicated to Albert Einstein

Special relativity is a theory of the structure of spacetime. It was introduced in Einstein's 1905 paper "On the Electrodynamics of Moving Bodies" (for the contributions of many other physicists see History of special relativity). Special relativity is based on two postulates which are contradictory in classical mechanics:

    The laws of physics are the same for all observers in uniform motion relative to one another (principle of relativity),
    The speed of light in a vacuum is the same for all observers, regardless of their relative motion or of the motion of the source of the light.

The resultant theory agrees with experiment better than classical mechanics, e.g. in the Michelson-Morley experiment that supports postulate 2, but also has many surprising consequences. Some of these are:

    Relativity of simultaneity: Two events, simultaneous for one observer, may not be simultaneous for another observer if the observers are in relative motion.
    Time dilation: Moving clocks are measured to tick more slowly than an observer's "stationary" clock.
    Length contraction: Objects are measured to be shortened in the direction that they are moving with respect to the observer.
    Mass–energy equivalence: E = mc2, energy and mass are equivalent and transmutable.
    Maximum speed is finite: No physical object, message or field line can travel faster than the speed of light in a vacuum.

The defining feature of special relativity is the replacement of the Galilean transformations of classical mechanics by the Lorentz transformations. (See Maxwell's equations of electromagnetism and introduction to special relativity).

General relativity

General relativity is a theory of gravitation developed by Einstein in the years 1907–1915. The development of general relativity began with the equivalence principle, under which the states of accelerated motion and being at rest in a gravitational field (for example when standing on the surface of the Earth) are physically identical. The upshot of this is that free fall is inertial motion; an object in free fall is falling because that is how objects move when there is no force being exerted on them, instead of this being due to the force of gravity as is the case in classical mechanics. This is incompatible with classical mechanics and special relativity because in those theories inertially moving objects cannot accelerate with respect to each other, but objects in free fall do so. To resolve this difficulty Einstein first proposed that spacetime is curved. In 1915, he devised the Einstein field equations which relate the curvature of spacetime with the mass, energy, and momentum within it.

Some of the consequences of general relativity are:

    Clocks run more slowly in deeper gravitational wells.This is called gravitational time dilation.
    Orbits precess in a way unexpected in Newton's theory of gravity. (This has been observed in the orbit of Mercury and in binary pulsars).
    Rays of light bend in the presence of a gravitational field.
    Rotating masses "drag along" the spacetime around them; a phenomenon termed "frame-dragging".
    The Universe is expanding, and the far parts of it are moving away from us faster than the speed of light.

Technically, general relativity is a metric theory of gravitation whose defining feature is its use of the Einstein field equations. The solutions of the field equations are metric tensors which define the topology of the spacetime and how objects move inertially.

Natural Environment

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The natural environment, encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species. The concept of the natural environment can be distinguished by components:

* Complete ecological units that function as natural systems without massive human intervention, including all vegetation, microorganisms, soil, rocks, atmosphere and natural phenomena that occur within their boundaries.

* Universal natural resources and physical phenomena that lack clear-cut boundaries, such as air, water, and climate, as well as energy, radiation, electric charge, and magnetism, not originating from human activity.

The natural environment is contrasted with the built environment, which comprises the areas and components that are strongly influenced by humans. A geographical area is regarded as a natural environment (with an indefinite article), if the human impact on it is kept under a certain limited level.

Composition

Earth science generally recognizes 4 spheres, the lithosphere, the hydrosphere, the atmosphere, and the biosphere as correspondent to rocks, water, air, and life. Some scientists include, as part of the spheres of the Earth, the cryosphere (corresponding to ice) as a distinct portion of the hydrosphere, as well as the pedosphere (corresponding to soil) as an active and intermixed sphere. Earth science (also known as geoscience, the geosciences or the Earth Sciences), is an all-embracing term for the sciences related to the planet Earth. There are four major disciplines in earth sciences, namely geography, geology, geophysics and geodesy. These major disciplines use physics, chemistry, biology, chronology and mathematics to build a qualitative and quantitative understanding of the principal areas or spheres of the Earth system.

Geological activity

The Earth's crust, or lithosphere, is the outermost solid surface of the planet and is chemically and mechanically different from underlying mantle. It has been generated largely by igneous processes in which magma (molten rock) cools and solidifies to form solid rock. Beneath the lithosphere lies the mantle which is heated by the decay of radioactive elements. The mantle though solid is in a state of rheic convection. This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics. Volcanoes result primarily from the melting of subducted crust material or of rising mantle at mid-ocean ridges and mantle plumes.

Solar System

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The Solar System consists of the Sun and the astronomical objects bound to it by gravity, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane. The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as "ice giants".

The Solar System is also home to two regions populated by smaller objects. The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie trans-Neptunian objects composed mostly of ices such as water, ammonia and methane. Within these two regions, five individual objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognized to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets. In addition to thousands of small bodies in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.

The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disc. The hypothetical Oort cloud, which acts as the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.
Six of the planets and three of the dwarf planets are orbited by natural satellites, usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other particles

Discovery and exploration

For many thousands of years, humanity, with a few notable exceptions, did not recognize the existence of the Solar System. People believed the Earth to be stationary at the center of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos,[1] Nicolaus Copernicus was the first to develop a mathematically predictive heliocentric system. His 17th-century successors, Galileo Galilei, Johannes Kepler and Isaac Newton, developed an understanding of physics which led to the gradual acceptance of the idea that the Earth moves around the Sun and that the planets are governed by the same physical laws that governed the Earth. In more recent times, improvements in the telescope and the use of unmanned spacecraft have enabled the investigation of geological phenomena such as mountains and craters, and seasonal meteorological phenomena such as clouds, dust storms and ice caps on the other planets.

Structure

The orbits of the bodies in the Solar System to scale (clockwise from top left)

The principal component of the Solar System is the Sun, a main sequence G2 star that contains 99.86 percent of the system's known mass and dominates it gravitationally. The Sun's four largest orbiting bodies, the gas giants, account for 99 percent of the remaining mass, with Jupiter and Saturn together comprising more than 90 percent.

Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are frequently at significantly greater angles to it. All the planets and most other objects also orbit with the Sun's rotation (counter-clockwise, as viewed from above the Sun's north pole). There are exceptions, such as Halley's Comet.

The overall structure of the charted regions of the Solar System consists of the Sun, four relatively small inner planets surrounded by a belt of rocky asteroids, and four gas giants surrounded by the outer Kuiper belt of icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the main asteroid belt. The outer Solar System is beyond the asteroids, including the four gas giant planets. Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune.

Kepler's laws of planetary motion describe the orbits of objects about the Sun. According to Kepler's laws, each object travels along an ellipse with the Sun at one focus. Objects closer to the Sun (with smaller semi-major axes) travel more quickly, as they are more affected by the Sun's gravity. On an elliptical orbit, a body's distance from the Sun varies over the course of its year. A body's closest approach to the Sun is called its perihelion, while its most distant point from the Sun is called its aphelion. The orbits of the planets are nearly circular, but many comets, asteroids and Kuiper belt objects follow highly elliptical orbits.

Due to the vast distances involved, many representations of the Solar System show orbits the same distance apart. In reality, with a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between it and the previous orbit. For example, Venus is approximately 0.33 astronomical units (AU) farther out from the Sun than Mercury, while Saturn is 4.3 AU out from Jupiter, and Neptune lies 10.5 AU out from Uranus. Attempts have been made to determine a correlation between these orbital distances (for example, the Titius-Bode law), but no such theory has been accepted.

Most of the planets in the Solar System possess secondary systems of their own, being orbited by planetary objects called natural satellites, or moons (two of which are larger than the planet Mercury), or, in the case of the four gas giants, by planetary rings; thin bands of tiny particles that orbit them in unison. Most of the largest natural satellites are in synchronous rotation, with one face permanently turned toward their parent.

The objects of the inner Solar System are composed mostly of rock, the collective name for compounds with high melting points, such as silicates, iron or nickel, that remained solid under almost all conditions in the protoplanetary nebula. Jupiter and Saturn are composed mainly of gases, the astronomical term for materials with extremely low melting points and high vapor pressure such as molecular hydrogen, helium, and neon, which were always in the gaseous phase in the nebula. Ices, like water, methane, ammonia, hydrogen sulfide and carbon dioxide, have melting points up to a few hundred kelvins, while their phase depends on the ambient pressure and temperature. They can be found as ices, liquids, or gases in various places in the Solar System, while in the nebula they were either in the solid or gaseous phase. Icy substances comprise the majority of the satellites of the giant planets, as well as most of Uranus and Neptune (the so-called "ice giants") and the numerous small objects that lie beyond Neptune's orbit.Together, gases and ices are referred to as volatiles.

Inner Solar System

The inner Solar System is the traditional name for the region comprising the terrestrial planets and asteroids.silicates and metals, the objects of the inner Solar System are relatively close to the Sun; the radius of this entire region is shorter than the distance between Jupiter and Saturn. Composed mainly of

Inner planets

The inner planets. From left to right: Mercury, Venus, Earth, and Mars (sizes to scale, interplanetary distances not)

The four inner or terrestrial planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of refractory minerals, such as the silicates which form their crusts and mantles, and metals such as iron and nickel, which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features such as rift valleys and volcanoes. The term inner planet should not be confused with inferior planet, which designates those planets which are closer to the Sun than Earth is (i.e. Mercury and Venus).
Mercury

    Mercury (0.4 AU from the Sun) is the closest planet to the Sun and the smallest planet in the Solar System (0.055 Earth masses). Mercury has no natural satellites, and its only known geological features besides impact craters are lobed ridges or rupes, probably produced by a period of contraction early in its history. Mercury's almost negligible atmosphere consists of atoms blasted off its surface by the solar wind. Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, and that it was prevented from fully accreting by the young Sun's energy.

Venus

    Venus (0.7 AU from the Sun) is close in size to Earth, (0.815 Earth masses) and like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere and evidence of internal geological activity. However, it is much drier than Earth and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C, most likely due to the amount of greenhouse gases in the atmosphere. No definitive evidence of current geological activity has been detected on Venus, but it has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is regularly replenished by volcanic eruptions.

Earth

    Earth (1 AU from the Sun) is the largest and densest of the inner planets, the only one known to have current geological activity, and is the only place in the universe where life is known to exist. Its liquid hydrosphere is unique among the terrestrial planets, and it is also the only planet where plate tectonics has been observed. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen. It has one natural satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System.

Asteroid belt

Image of the main asteroid belt and the Trojan asteroids

Asteroids are mostly small Solar System bodies composed mainly of refractory rocky and metallic minerals.

The main asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter.

Asteroids range in size from hundreds of kilometres across to microscopic. All asteroids save the largest, Ceres, are classified as small Solar System bodies, but some asteroids such as Vesta and Hygieia may be reclassed as dwarf planets if they are shown to have achieved hydrostatic equilibrium.

The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter. Despite this, the total mass of the main belt is unlikely to be more than a thousandth of that of the Earth. The main belt is very sparsely populated; spacecraft routinely pass through without incident. Asteroids with diameters between 10 and 10−4 m are called meteoroids.
Ceres

Ceres (2.77 AU) is the largest body in the asteroid belt and is classified as a dwarf planet. It has a diameter of slightly under 1000 km, and a mass large enough for its own gravity to pull it into a spherical shape. Ceres was considered a planet when it was discovered in the 19th century, but was reclassified as an asteroid in the 1850s as further observation revealed additional asteroids. It was again reclassified in 2006 as a dwarf planet.

Asteroid groups

Asteroids in the main belt are divided into asteroid groups and families based on their orbital characteristics. Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners. The asteroid belt also contains main-belt comets which may have been the source of Earth's water.

Trojan asteroids are located in either of Jupiter's L4 or L5 points (gravitationally stable regions leading and trailing a planet in its orbit); the term "Trojan" is also used for small bodies in any other planetary or satellite Lagrange point. Hilda asteroids are in a 2:3 resonance with Jupiter; that is, they go around the Sun three times for every two Jupiter orbits.

The inner Solar System is also dusted with rogue asteroids, many of which cross the orbits of the inner planets.

Outer Solar System

The outer region of the Solar System is home to the gas giants and their large moons. Many short period comets, including the centaurs, also orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles such as water, ammonia and methane, than the rocky denizens of the inner Solar System, as the colder temperatures allow these compounds to remain solid.

Outer planets

From top to bottom: Neptune, Uranus, Saturn, and Jupiter (not to scale)

The four outer planets, or gas giants (sometimes called Jovian planets), collectively make up 99 percent of the mass known to orbit the Sun. Jupiter and Saturn are each many tens of times the mass of the Earth and consist overwhelmingly of hydrogen and helium; Uranus and Neptune are far less massive (<20 Earth masses) and possess more ices in their makeup. For these reasons, some astronomers suggest they belong in their own category, “ice giants.” All four gas giants have rings, although only Saturn's ring system is easily observed from Earth. The term outer planet should not be confused with superior planet, which designates planets outside Earth's orbit and thus includes both the outer planets and Mars.

Jupiter

Jupiter (5.2 AU), at 318 Earth masses, is 2.5 times the mass of all the other planets put together. It is composed largely of hydrogen and helium. Jupiter's strong internal heat creates a number of semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot.

Jupiter has 63 known satellites. The four largest, Ganymede, Callisto, Io, and Europa, show similarities to the terrestrial planets, such as volcanism and internal heating. Ganymede, the largest satellite in the Solar System, is larger than Mercury.

Saturn

Saturn (9.5 AU), distinguished by its extensive ring system, has several similarities to Jupiter, such as its atmospheric composition and magnetosphere. Although Saturn has 60% of Jupiter's volume, it is less than a third as massive, at 95 Earth masses, making it the least dense planet in the Solar System. The rings of Saturn are made up of small ice and rock particles.

Saturn has 62 confirmed satellites; two of which, Titan and Enceladus, show signs of geological activity, though they are largely made of ice. Titan, the second largest moon in the Solar System, is larger than Mercury and the only satellite in the Solar System with a substantial atmosphere.

Uranus

Uranus (19.6 AU), at 14 Earth masses, is the lightest of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. It has a much colder core than the other gas giants, and radiates very little heat into space.

Uranus has 27 known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel and Miranda.

Neptune

Neptune (30 AU), though slightly smaller than Uranus, is more massive (equivalent to 17 Earths) and therefore more dense. It radiates more internal heat, but not as much as Jupiter or Saturn.

Neptune has 13 known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen. Triton is the only large satellite with a retrograde orbit. Neptune is accompanied in its orbit by a number of minor planets, termed Neptune Trojans, that are in 1:1 resonance with it.

Comets

Comet Hale-Bopp

Comets are small Solar System bodies, typically only a few kilometres across, composed largely of volatile ices. They have highly eccentric orbits, generally a perihelion within the orbits of the inner planets and an aphelion far beyond Pluto. When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to sublimate and ionise, creating a coma: a long tail of gas and dust often visible to the naked eye.

Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are believed to originate in the Kuiper belt, while long-period comets, such as Hale-Bopp, are believed to originate in the Oort cloud. Many comet groups, such as the Kreutz Sungrazers, formed from the breakup of a single parent. Some comets with hyperbolic orbits may originate outside the Solar System, but determining their precise orbits is difficult. Old comets that have had most of their volatiles driven out by solar warming are often categorised as asteroids.

Centaurs

The centaurs are icy comet-like bodies with a semi-major axis greater than Jupiter (5.5 AU) and less than Neptune (30 AU). The largest known centaur, 10199 Chariklo, has a diameter of about 250 km. The first centaur discovered, 2060 Chiron, has also been classified as comet (95P) since it develops a coma just as comets do when they approach the Sun.

Trans-Neptunian region

The area beyond Neptune, or the "trans-Neptunian region", is still largely unexplored. It appears to consist overwhelmingly of small worlds (the largest having a diameter only a fifth that of the Earth and a mass far smaller than that of the Moon) composed mainly of rock and ice. This region is sometimes known as the "outer Solar System", though others use that term to mean the region beyond the asteroid belt.

Kuiper belt

Plot of all known Kuiper belt objects, set against the four outer planets

The Kuiper belt, the region's first formation, is a great ring of debris similar to the asteroid belt, but composed mainly of ice. It extends between 30 and 50 AU from the Sun. Though it contains at least three dwarf planets, it is composed mainly of small Solar System bodies. However, many of the largest Kuiper belt objects, such as Quaoar, Varuna, and Orcus, may be reclassified as dwarf planets. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of the Earth. Many Kuiper belt objects have multiple satellites, and most have orbits that take them outside the plane of the ecliptic.

The Kuiper belt can be roughly divided into the "classical" belt and the resonances. Resonances are orbits linked to that of Neptune (e.g. twice for every three Neptune orbits, or once for every two). The first resonance begins within the orbit of Neptune itself. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 AU to 47.7 AU. Members of the classical Kuiper belt are classified as cubewanos, after the first of their kind to be discovered, (15760) 1992 QB₁, and are still in near primordial, low-eccentricity orbits.

Pluto and Charon

Comparison of Eris, Pluto, Makemake, Haumea, Sedna, Orcus, 2007 OR₁₀, Quaoar, and Earth (all to scale)

Pluto (39 AU average), a dwarf planet, is the largest known object in the Kuiper belt. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet. Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion.

Charon, Pluto's largest moon, is sometimes described as part of a binary system with Pluto, as the two bodies orbit a barycenter of gravity above their surfaces (i.e., they appear to "orbit each other"). Beyond Charon, two much smaller moons, Nix and Hydra, orbit within the system.

Pluto has a 3:2 resonance with Neptune, meaning that Pluto orbits twice round the Sun for every three Neptunian orbits. Kuiper belt objects whose orbits share this resonance are called plutinos.

Haumea and Makemake

Haumea (43.34 AU average), and Makemake (45.79 AU average), while smaller than Pluto, are the largest known objects in the classical Kuiper belt (that is, they are not in a confirmed resonance with Neptune). Haumea is an egg-shaped object with two moons. Makemake is the brightest object in the Kuiper belt after Pluto. Originally designated 2003 EL₆₁ and 2005 FY₉ respectively, they were given names and designated dwarf planets in 2008. Their orbits are far more inclined than Pluto's, at 28° and 29°.

Scattered disc

The scattered disc, which overlaps the Kuiper belt but extends much further outwards, is thought to be the source of short-period comets. Scattered disc objects are believed to have been ejected into erratic orbits by the gravitational influence of Neptune's early outward migration. Most scattered disc objects (SDOs) have perihelia within the Kuiper belt but aphelia as far as 150 AU from the Sun. SDOs' orbits are also highly inclined to the ecliptic plane, and are often almost perpendicular to it. Some astronomers consider the scattered disc to be merely another region of the Kuiper belt, and describe scattered disc objects as "scattered Kuiper belt objects." Some astronomers also classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc.

Eris

Eris (68 AU average) is the largest known scattered disc object, and caused a debate about what constitutes a planet, since it is at least 5% larger than Pluto with an estimated diameter of 2400 km (1500 mi). It is the largest of the known dwarf planets. It has one moon, Dysnomia. Like Pluto, its orbit is highly eccentric, with a perihelion of 38.2 AU (roughly Pluto's distance from the Sun) and an aphelion of 97.6 AU, and steeply inclined to the ecliptic plane.

Farthest regions

The point at which the Solar System ends and interstellar space begins is not precisely defined, since its outer boundaries are shaped by two separate forces: the solar wind and the Sun's gravity. The outer limit of the solar wind's influence is roughly four times Pluto's distance from the Sun; this heliopause is considered the beginning of the interstellar medium. However, the Sun's Roche sphere, the effective range of its gravitational dominance, is believed to extend up to a thousand times farther.

Heliopause

The Voyagers entering the heliosheath

The heliosphere is divided into two separate regions. The solar wind travels at roughly 400 km/s until it collides with the interstellar wind; the flow of plasma in the interstellar medium. The collision occurs at the termination shock, which is roughly 80–100 AU from the Sun upwind of the interstellar medium and roughly 200 AU from the Sun downwind. Here the wind slows dramatically, condenses and becomes more turbulent,heliosheath. This structure is believed to look and behave very much like a comet's tail, extending outward for a further 40 AU on the upwind side but tailing many times that distance downwind; but evidence from the Cassini and Interstellar Boundary Explorer spacecraft has suggested that it is in fact forced into a bubble shape by the constraining action of the interstellar magnetic field. Both Voyager 1 and Voyager 2 are reported to have passed the termination shock and entered the heliosheath, at 94 and 84 AU from the Sun, respectively. The outer boundary of the heliosphere, the heliopause, is the point at which the solar wind finally terminates and is the beginning of interstellar space. forming a great oval structure known as the

The shape and form of the outer edge of the heliosphere is likely affected by the fluid dynamics of interactions with the interstellar medium as well as solar magnetic fields prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9 AU (roughly 900 million miles) farther than the southern hemisphere. Beyond the heliopause, at around 230 AU, lies the bow shock, a plasma "wake" left by the Sun as it travels through the Milky Way.

No spacecraft have yet passed beyond the heliopause, so it is impossible to know for certain the conditions in local interstellar space. It is expected that NASA's Voyager spacecraft will pass the heliopause some time in the next decade and transmit valuable data on radiation levels and solar wind back to the Earth. How well the heliosphere shields the Solar System from cosmic rays is poorly understood. A NASA-funded team has developed a concept of a "Vision Mission" dedicated to sending a probe to the heliosphere.

Oort cloud

An artist's rendering of the Oort Cloud, the Hills Cloud, and the Kuiper belt (inset)

The hypothetical Oort cloud is a spherical cloud of up to a trillion icy objects that is believed to be the source for all long-period comets and to surround the Solar System at roughly 50,000 AU (around 1 light-yeargalactic tide, the tidal force exerted by the Milky Way. (LY)), and possibly to as far as 100,000 AU (1.87 LY). It is believed to be composed of comets which were ejected from the inner Solar System by gravitational interactions with the outer planets. Oort cloud objects move very slowly, and can be perturbed by infrequent events such as collisions, the gravitational effects of a passing star, or the

Sedna

90377 Sedna (525.86 AU average) is a large, reddish Pluto-like object with a gigantic, highly elliptical orbit that takes it from about 76 AU at perihelion to 928 AU at aphelion and takes 12,050 years to complete. Mike Brown, who discovered the object in 2003, asserts that it cannot be part of the scattered disc or the Kuiper belt as its perihelion is too distant to have been affected by Neptune's migration. He and other astronomers consider it to be the first in an entirely new population, which also may include the object 2000 CR₁₀₅, which has a perihelion of 45 AU, an aphelion of 415 AU, and an orbital period of 3,420 years. Sedna is very likely a dwarf planet, though its shape has yet to be determined with certainty. Brown terms this population the "Inner Oort cloud," as it may have formed through a similar process, although it is far closer to the Sun.

Boundaries

Much of our Solar System is still unknown. The Sun's gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light years (125,000 AU). Lower estimates for the radius of the Oort cloud, by contrast, do not place it farther than 50,000 AU. Despite discoveries such as Sedna, the region between the Kuiper belt and the Oort cloud, an area tens of thousands of AU in radius, is still virtually unmapped. There are also ongoing studies of the region between Mercury and the Sun. Objects may yet be discovered in the Solar System's uncharted regions.

Galactic context

Location of the Solar System within our galaxy

The Solar System is located in the Milky Way galaxy, a barred spiral galaxy with a diameter of about 100,000 light-years containing about 200 billion stars. Our Sun resides in one of the Milky Way's outer spiral arms, known as the Orion Arm or Local Spur. The Sun lies between 25,000 and 28,000 light years from the Galactic Centre, and its speed within the galaxy is about 220 kilometres per second, so that it completes one revolution every 225–250 million years. This revolution is known as the Solar System's galactic year. The solar apex, the direction of the Sun's path through interstellar space, is near the constellation of Hercules in the direction of the current location of the bright star Vega. The plane of the Solar System's ecliptic lies at an angle of about 60° to the galactic plane.

The Solar System's location in the galaxy is very likely a factor in the evolution of life on Earth. Its orbit is close to being circular and is at roughly the same speed as that of the spiral arms, which means it passes through them only rarely. Since spiral arms are home to a far larger concentration of potentially dangerous supernovae, this has given Earth long periods of interstellar stability for life to evolve. The Solar System also lies well outside the star-crowded environs of the galactic centre. Near the centre, gravitational tugs from nearby stars could perturb bodies in the Oort Cloud and send many comets into the inner Solar System, producing collisions with potentially catastrophic implications for life on Earth. The intense radiation of the galactic centre could also interfere with the development of complex life. Even at the Solar System's current location, some scientists have hypothesised that recent supernovae may have adversely affected life in the last 35,000 years by flinging pieces of expelled stellar core towards the Sun as radioactive dust grains and larger, comet-like bodies.

Neighbourhood

The immediate galactic neighbourhood of the Solar System is known as the Local Interstellar Cloud or Local Fluff, an area of denser cloud in an otherwise sparse region known as the Local Bubble, an hourglass-shaped cavity in the interstellar medium roughly 300 light years across. The bubble is suffused with high-temperature plasma that suggests it is the product of several recent supernovae.

There are relatively few stars within ten light years (95 trillion km) of the Sun. The closest is the triple star system Alpha Centauri, which is about 4.4 light years away. Alpha Centauri A and B are a closely tied pair of Sun-like stars, while the small red dwarf Alpha Centauri C (also known as Proxima Centauri) orbits the pair at a distance of 0.2 light years. The stars next closest to the Sun are the red dwarfs Barnard's Star (at 5.9 light years), Wolf 359 (7.8 light years) and Lalande 21185 (8.3 light years). The largest star within ten light years is Sirius, a bright main sequence star roughly twice the Sun's mass and orbited by a white dwarf called Sirius B. It lies 8.6 light years away. The remaining systems within ten light years are the binary red dwarf system Luyten 726-8 (8.7 light years) and the solitary red dwarf Ross 154 (9.7 light years). Our closest solitary sun-like star is Tau Ceti, which lies 11.9 light years away. It has roughly 80 percent the Sun's mass, but only 60 percent its luminosity. The closest known extrasolar planet to the Sun lies around the star Epsilon Eridani, a star slightly dimmer and redder than the Sun, which lies 10.5 light years away. Its one confirmed planet, Epsilon Eridani b, is roughly 1.5 times Jupiter's mass and orbits its star every 6.9 years.

Formation and evolution

The Solar System formed from the gravitational collapse of a giant molecular cloud 4.568 billion years ago. This initial cloud was likely several light-years across and probably birthed several stars.

As the region that would become the Solar System, known as the pre-solar nebula, collapsed, conservation of angular momentum made it rotate faster. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc. As the contracting nebula rotated, it began to flatten into a spinning protoplanetary disc with a diameter of roughly 200 AU and a hot, dense protostar at the centre. At this point in its evolution, the Sun is believed to have been a T Tauri star. Studies of T Tauri stars show that they are often accompanied by discs of pre-planetary matter with masses of 0.001–0.1 solar masses, with the vast majority of the mass of the nebula in the star itself. The planets formed by accretion from this disk.

Within 50 million years, the pressure and density of hydrogen in the centre of the protostar became great enough for it to begin thermonuclear fusion. The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved, with the thermal energy countering the force of gravitational contraction. At this point the Sun became a full-fledged main sequence star.

The Solar System as we know it today will last until the Sun begins its evolution off of the main sequence of the Hertzsprung-Russell diagram. As the Sun burns through its supply of hydrogen fuel, the energy output supporting the core tends to decrease, causing it to collapse in on itself. This increase in pressure heats the core, so it burns even faster. As a result, the Sun is growing brighter at a rate of roughly ten percent every 1.1 billion years.

Around 5.4 billion years from now, the hydrogen in the core of the Sun will have been entirely converted to helium, ending the main sequence phase. As the hydrogen reactions shut down, the core will contract further, increasing pressure and temperature, causing fusion to commence via the helium process. Helium in the core burns at a much hotter temperature, and the energy output will be much greater than during the hydrogen process. At this time, the outer layers of the Sun will expand to roughly up to 260 times its current diameter; the Sun will become a red giant. Because of its vastly increased surface area, the surface of the Sun will be considerably cooler than it is on the main sequence (2600 K at the coolest).

Eventually, helium in the core will exhaust itself at a much faster rate than the hydrogen, and the Sun's helium burning phase will be but a fraction of the time compared to the hydrogen burning phase. The Sun is not massive enough to commence fusion of heavier elements, and nuclear reactions in the core will dwindle. Its outer layers will fall away into space, leaving a white dwarf, an extraordinarily dense object, half the original mass of the Sun but only the size of the Earth. The ejected outer layers will form what is known as a planetary nebula, returning some of the material that formed the Sun to the interstellar medium.

Galaxy

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A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas dust, and an important but poorly understood component tentatively dubbed dark matter. The name is from the Greek root galaxias [γαλαξίας], literally meaning "milky", a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars, up to giants with a hundred trillion (1014) stars, all orbiting the galaxy's center of mass. Galaxies may contain many star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.

Historically, galaxies have been categorized according to their apparent shape (usually referred to as their visual morphology). A common form is the elliptical galaxy, which has an ellipse-shaped light profile. Spiral galaxies are disk-shaped assemblages with dusty, curving arms. Galaxies with irregular or unusual shapes are known as irregular galaxies, and typically result from disruption by the gravitational pull of neighboring galaxies. Such interactions between nearby galaxies, which may ultimately result in galaxies merging, may induce episodes of significantly increased star formation, producing what is called a starburst galaxy. Small galaxies that lack a coherent structure could also be referred to as irregular galaxies.

There are probably more than 170 billion (1.7 × 1011) galaxies in the observable universe. Most galaxies are 1,000 to 100,000 parsecs in diameter and are usually separated by distances on the order of millions of parsecs (or megaparsecs). Intergalactic space (the space between galaxies) is filled with a tenuous gas of an average density less than one atom per cubic meter. The majority of galaxies are organized into a hierarchy of associations called clusters, which, in turn, can form larger groups called superclusters. These larger structures are generally arranged into sheets and filaments, which surround immense voids in the universe.
Although it is not yet well understood, dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that supermassive black holes may exist at the center of many, if not all, galaxies. They are proposed to be the primary cause of active galactic nuclei found at the core of some galaxies. The Milky Way galaxy appears to harbor at least one such object within its nucleus

Etymology

The word galaxy derives from the Greek term for our own galaxy, galaxias (γαλαξίας), or kyklos galaktikos, meaning "milky circle" for its appearance in the sky. In Greek mythology, Zeus places his son born by a mortal woman, the infant Heracles, on Hera's breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away and a jet of her milk sprays the night sky, producing the faint band of light known as the Milky Way.

In the astronomical literature, the capitalized word 'Galaxy' is used to refer to our galaxy, the Milky Way, to distinguish it from the billions of other galaxies. The term Milky Way first appeared in the English language in a poem by Chaucer.

    "See yonder, lo, the Galaxyë
     Which men clepeth the Milky Wey,
     For hit is whyt."
    —Geoffrey Chaucer. The House of Fame, c. 1380.

When William Herschel constructed his catalog of deep sky objects, he used the name spiral nebula for certain objects such as M31. These would later be recognized as immense conglomerations of stars, when the true distance to these objects began to be appreciated, and they would be termed island universes. However, the word Universe was understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies.

Paleontology

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Paleontology (British: palaeontology) is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments (their paleoecology). As a "historical science" it tries to explain causes rather than conduct experiments to observe effects. Paleontological observations have been documented as far back as the 5th century BC. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. Fossils found in China since the 1990s have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds and mammals. Paleontology lies on the border between biology and geology, and shares with archaeology a border that is difficult to define. It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics and engineering. As knowledge has increased, paleontology has developed specialized subdivisions, some of which focus on different types of fossil organisms while others study ecological and environmental history, such as ancient climates.

Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy. Classifying ancient organisms is also difficult, as many do not fit well into the Linnean taxonomy that is commonly used for classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring how similar the DNA is in their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend.

Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost all the way back to when Earth became capable of supporting life, about 3,800 million years ago. For about half of that time the only life was single-celled micro-organisms, mostly in microbial mats that formed ecosystems only a few millimeters thick. Earth's atmosphere originally contained virtually no oxygen, and its oxygenation began about 2,400 million years ago. This may have caused an accelerating increase in the diversity and complexity of life, and early multicellular plants and fungi have been found in rocks dated from 1,700 to 1,200 million years ago. The earliest multicellular animal fossils are much later, from about 580 million years ago, but animals diversified very rapidly and there is a lively debate about whether most of this happened in a relatively short Cambrian explosion or started earlier but has been hidden by lack of fossils. All of these organisms lived in water, but plants and invertebrates started colonizing land from about 490 million years ago and vertebrates followed them about 370 million years ago. The first dinosaurs appeared about 230 million years ago and birds evolved from one dinosaur group about 150 million years ago. During the time of the dinosaurs, mammals' ancestors survived only as small, mainly nocturnal insectivores, but after the non-avian dinosaurs became extinct in the Cretaceous–Tertiary extinction event 65 million years ago mammals diversified rapidly. Flowering plants appeared and rapidly diversified between 130 million years ago and 90 million years ago, possibly helped by coevolution with pollinating insects. Social insects appeared around the same time and, although they have relatively few species, now form over 50% of the total mass of all insects. The upright-walking common ancestor of humans and chimpanzees Sahelanthropus tchadensis appeared around 6 to 7 million years ago, and anatomically modern humans appeared under 200,000 years ago. The course of evolution has been changed several times by mass extinctions that wiped out previously dominant groups and allowed other to rise from obscurity to become major components of ecosystems.

Seismology

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Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes (such as explosions). A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of earth motion as a function of time is called a seismogram.

Seismic waves

Earthquakes, and other sources, produce different types of seismic waves which travel through rock, and provide an effective way to image both sources and structures deep within the Earth. There are three basic types of seismic waves in solids: P-waves, S-waves (both body waves) and interface waves. The two basic kinds of surface waves (Rayleigh and Love) which travel along a solid-air interface, can be fundamentally explained in terms of interacting P- and/or S-waves.

Propagation of seismic wave in the ground and the effect of presence of land mine.

Pressure waves or Primary waves (P-waves), are longitudinal waves that travel at maximum velocity within solids and are therefore the first waves to appear on a seismogram.

S-waves, also called shear or secondary waves, are transverse waves that travel more slowly than P-waves and thus appear later than P-waves on a seismogram. Particle motion is perpendicular to the direction of wave propagation. Shear waves do not exist in fluids with essentially no shear strength, such as air or water.

Surface waves travel more slowly than P-waves and S-waves, but because they are guided by the surface of the Earth (and their energy is thus trapped near the Earth's surface) they can be much larger in amplitude than body waves, and can be the largest signals seen in earthquake seismograms. They are particularly strongly excited when the seismic source is close to the surface of the Earth, such as the case of a shallow earthquake or explosion.

For large enough earthquakes, one can observe the normal modes of the Earth. These modes are excited as discrete frequencies and can be observed for days after the generating event. The first observations were made in the 1960s as the advent of higher fidelity instruments coincided with two of the largest earthquakes of the 20th century - the 1960 Great Chilean earthquake and the 1964 Great Alaskan earthquake. Since then, the normal modes of the Earth have given us some of the strongest constraints on the deep structure of the Earth.

One of the earliest important discoveries (suggested by Richard Dixon Oldham in 1906 and definitively shown by Harold Jeffreys in 1926) was that the outer core of the Earth is liquid. Pressure waves (P-waves) pass through the core. Transverse or shear waves (S-waves) that shake side-to-side require rigid material so they do not pass through the outer core. Thus, the liquid core causes a "shadow" on the side of the planet opposite of the earthquake where no direct S-waves are observed. The reduction in P-wave velocity of the outer core also causes a substantial delay for P waves penetrating the core from the (seismically faster velocity) mantle.

Seismic waves produced by explosions or vibrating controlled sources are one of the primary methods of underground exploration in geophysics (in addition to many different electromagnetic methods such as induced polarization and magnetotellurics). Controlled source seismology has been used to map salt domes, faults, anticlines and other geologic traps in petroleum-bearing rocks, geological faults, rock types, and long-buried giant meteor craters. For example, the Chicxulub impactor, which is believed to have killed the dinosaurs, was localized to Central America by analyzing ejecta in the cretaceous boundary, and then physically proven to exist using seismic maps from oil exploration.

Using seismic tomography with earthquake waves, the interior of the Earth has been completely mapped to a resolution of several hundred kilometers. This process has enabled scientists to identify convection cells, mantle plumes and other large-scale features of the inner Earth.

Seismographs are instruments that sense and record the motion of the Earth. Networks of seismographs today continuously monitor the seismic environment of the planet, allowing for the monitoring and analysis of global earthquakes and tsunami warnings, as well as recording a variety of seismic signals arising from non-earthquake sources ranging from explosions (nuclear and chemical), to pressure variations on the ocean floor induced by ocean waves (the global microseism), to cryospheric events associated with large icebergs and glaciers. Above-ocean meteor strikes as large as ten kilotons of TNT, (equivalent to about 4.2 × 1013 J of effective explosive force) have been recorded by seismographs. A major motivation for the global instrumentation of the Earth with seismographs has been for the monitoring of nuclear testing.

One of the first attempts at the scientific study of earthquakes followed the 1755 Lisbon earthquake. Other especially notable earthquakes that spurred major developments in the science of seismology include the 1857 Basilicata earthquake, 1906 San Francisco earthquake, the 1964 Alaska earthquake and the 2004 Sumatra-Andaman earthquake. An extensive list of famous earthquakes can be found on the List of earthquakes page.
Earthquake prediction

Forecasting a probable timing, location, magnitude and other important features of a forthcoming seismic event is called earthquake prediction. Most seismologists do not believe that a system to provide timely warnings for individual earthquakes has yet been developed, and many believe that such a system would be unlikely to give significant warning of impending seismic events. More general forecasts, however, are routinely used to establish seismic hazard. Such forecasts estimate the probability of an earthquake of a particular size affecting a particular location within a particular time span and they are routinely used in earthquake engineering.

Various attempts have been made by seismologists and others to create effective systems for precise earthquake predictions, including the VAN method. Such methods have yet to be generally accepted in the seismology community.

Geoinformatics

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Geoinformatics is the science and the technology which develops and uses information science infrastructure to address the problems of geography, geosciences and related branches of engineering.

Overview

Geoinformatics has been described as "the science and technology dealing with the structure and character of spatial information, its capture, its classification and qualification, its storage, processing, portrayal and dissemination, including the infrastructure necessary to secure optimal use of this information" or "the art, science or technology dealing with the acquisition, storage, processing production, presentation and dissemination of geoinformation" .

Geomatics is a similarly used term which encompasses geoinformatics, but geomatics focuses on surveying. Geoinformatics has at its core the technologies supporting the processes of acquiring, analyzing and visualizing spatial data. Both geomatics and geoinformatics include and rely heavily upon the theory and practical implications of geodesy.

Geography and earth science increasingly rely on digital spatial data acquired from remotely sensed images analyzed by geographical information systems (GIS) and visualized on paper or the computer screen .

Geoinformatics combines geospatial analysis and modeling, development of geospatial databases, information systems design, human-computer interaction and both wired and wireless networking technologies. Geoinformatics uses geocomputation and geovisualization for analyzing geoinformation.

Branches of geoinformatics include:

Cartography	Geodesy	Geographic Information Systems	Global Navigation Satellite Systems
Photogrammetry	Remote sensing	Web mapping

Applications

Many fields benefit from geoinformatics, including urban planning and land use management, in-car navigation systems, virtual globes, public health, local and national gazetteer management, environmental modeling and analysis, military, transport network planning and management, agriculture, meteorology and climate change, oceanography and coupled ocean and atmosphere modelling, business location planning, architecture and archeological reconstruction, telecommunications, criminology and crime simulation, aviation and maritime transport.