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May 15, 1836: On this date in science, Francis Baily (1774-1844), an English astronomer, saw beads of sunlight shining along the edge of the moon’s silhouette during an eclipse of the sun.

It was an annular eclipse – nowadays often called a ring of fire eclipse – meaning that the moon was too far away in its monthly orbit around Earth to appear large enough in our sky to cover the sun completely. Baily saw beads of light shining around the darkened lunar limb (edge of the moon).

Baily’s discovery

Baily’s goal was to time the length of the annular phase of the eclipse. He would do this by recording the time during which the moon was inside the sun’s disk. He would start timing as soon as a line of sunlight appeared along the trailing edge of the moon.

Baily expected to observe a nice, smooth line of sunlight along one edge of the moon. Imagine his surprise as he watched and waited for it to appear – while observing with a filtered 2.6-inch, f/16 refracting telescope – at 40x magnification. Instead of seeing a smooth line of sunlight, he saw a broken line of light and dark spots.

Don’t start that stopwatch yet, Mr. Baily!

Baily and others have commented that the line of light and dark spots resembled beads on a string. And, as the seconds ticked by, Baily saw the dark spots decrease in both number and size. And he saw the light spots increase in both number and size, until there was a fine line of sunlight around the edge of the moon.

Okay, now start the stopwatch!

But after the moon was completely inside the solar disk, the moon did look “smooth and circular” to him. At least four other local observers confirmed this observation during this eclipse.

Sunlight shining through lunar valleys

Later, others realized that these beads of light appeared due to mountains and valleys, crater walls, and other topographic features extending above the limb, or edge, of the moon as seen from Earth. This phenomenon earned the name Baily’s beads. And you can see it during total eclipses, too, just before the moon covers the sun completely. A video of Baily’s beads is here.

Baily published his discovery in the Monthly Notices of the Royal Astronomical Society in December of 1836. In a talk to the Royal Astronomical Society, he mentioned that he knew of only one other person who had seen these before, that being Jean Henri van Swinden (1746–1823), a Dutch scientist.

Today, Baily’s beads are one of the eclipse effects that amateur astronomers around the world – using proper eye protection – watch for during annular and total eclipses of the sun.

Baily’s beads during a total eclipse

Baily discovered the beads during an annular eclipse, but they’re best known for being visible during a total eclipse. Let’s look at the process during a total eclipse.

During a total eclipse, the moon moves across a sun that takes up the same amount of sky. As the leading edge of the moon moves toward covering the remainder of the sun, dark spots interrupt the last bit of sunlight. Those are lunar mountains. Totality has not yet begun, as sunlight is still peeking between these dark spots.

As the seconds tick by, the sunlight decreases, and the dark areas increase until there is only one spot of light on the limb of the moon: the diamond ring. When that final bright spot disappears, the total eclipse begins. Remove the solar filters for a fantastic view.

As the total phase draws to a close, the effects resume in reverse order. On the trailing side of the moon the sunlight appears. First, the diamond ring. Next, Baily’s beads. Watch a video of Baily’s beads during the August 21, 2017, total eclipse here.

The Baily’s beads phase is unappreciated during total eclipses. The main show is totality, and observers are typically preparing to remove their solar filters while Baily’s beads and the diamond ring are occurring. And those Baily’s beads at the end of totality? They are accompanied by sighs as the total phase comes to an abrupt end. But you can watch the phenomena at the end of the total eclipse with unfiltered and dark-adapted eyes, so they might appear brighter and more noteworthy than those leading into the total phase.

Baily’s beads during an annular eclipse

Here is the process during an annular eclipse, the type that Baily saw. To start, the moon appears smaller than the sun, so you must use filters the entire time. At the center of the annular eclipse, you see a ring of the sun around the moon. And the episode begins on the trailing, not the leading, edge of the moon. As the last bit of the moon moves onto the sun, the uneven dark limb (edge) of the moon produces bright spots. These bright spots increase in number and size until the whole edge of the moon is a bright arc of sunlight.

That is what Baily saw. Toward the end of the annular phase of the eclipse, now looking toward the leading edge of the moon, that bright arc of sunlight begins to be interrupted by dark spots, growing in size. A video of Baily’s beads during an annular eclipse is here.

Extending the beads

Is there a way to make those beads visible for a longer length of time? Yes, there are two ways. One is to hop onto a jet and zoom along the path of the eclipse. This will also extend the length of the total phase of the eclipse.

The other way is to set up near the edge of the central path of the eclipse. The typical eclipse shows the main event, whether annular or total, only along a path on the earth that is about 100 miles (160 km) wide. Sit in the center of that path and the eclipse phase will last longer than near the north or south limit of this path. But if you go near the north or south limit, the Baily’s beads phase will last longer, at the sacrifice of the central phase. A video of Baily’s beads lasting more than two minutes is here.

Baily’s beads or Halley’s beads?

On April 22, 1715 (Julian calendar, or May 3, 1715, Gregorian calendar) Edmond Halley (1656-1742) observed a total solar eclipse from London. He predicted the eclipse, and so it is often referred to as Halley’s Eclipse. During this total eclipse, Halley observed Baily’s beads too, 59 years before Baily was even born. Here is Halley’s description:

About two Minutes before the Total Immersion, the remaining part of the Sun was reduced to a very fine Horn, whose Extremeties seemed to lose their Acuteness, and to become round like Stars … which Appearance could proceed from no other Cause but the Inequalities of the Moon’s Surface, there being some elevated parts thereof near the Moon’s Southern Pole, by whose Interposition part of that exceedingly fine Filament of Light was intercepted.

This is an excellent description of Baily’s beads, even though Halley hit the “shift” key a few too many times!

Edmond Halley was the first to observe and identify the event we now call Baily’s beads, yet they are not named after him. What is named after Edmond Halley?

Halley’s Comet, which he did not discover, but he did predict its return.
Halley’s Eclipse in 1715, which he also predicted.
Halley, the crater on the moon, named long after Halley passed away.
Halley, the crater on Mars, named in 1973.
Halley Research Station, in Antarctica, established in 1956. Edmond Halley never went to Antarctica, nor to the moon nor Mars, for that matter.
Halley’s Mount, a hill on the island of Saint Helena, from where Halley observed the southern sky.

But we don’t have “Halley’s beads,” even though he discovered and defined them. One suggestion is to refer to the beads seen during the annular eclipses as Baily’s beads and the ones seen during the total eclipses as Halley’s beads. Then Edmond Halley would finally be recognized for something he discovered.

When’s your next chance to spot Baily’s beads? Read more: Total solar eclipse dazzles observers on August 12, 2026.

Bottom line: May 15, 1836: Francis Baily, an English astronomer, saw light shining through lunar ridges during an eclipse of the sun. These are now known as Baily’s beads.

The post Baily’s beads seen during a solar eclipse today in 1836 first appeared on EarthSky.

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On this day in May 6, 1968: Neil Armstrong’s close call

In 1969, Neil Armstrong became the first human to set foot on the moon. But things could have been very different. More than a year earlier, he narrowly escaped from a dramatic accident during training.

He was flying in the Lunar Landing Research Vehicle (LLRV) at Ellington Air Force Base near Houston. The LLRV had been designed to simulate a descent to the moon’s surface, and all the lunar astronauts trained in it. That day, while Armstrong was piloting, a leaking propellant caused a total failure of his flight controls.

He attempted to right the vehicle, but to no avail. The craft plummeted to the ground … and he ejected just before impact. See the dramatic footage of Neil Armstrong’s close call above.

Armstrong made it through unscathed

Armstrong was fine. He bit his tongue hard during his landing by parachute, but otherwise was uninjured. Smithsonian magazine described this encounter between Armstrong and another astronaut later that day:

… astronaut Alan Bean saw Armstrong that afternoon at his desk in the astronaut office. Bean then heard colleagues in the hall talking about the accident, and asked them: ‘When did this happen?’, ‘About an hour ago,’ they replied.

Bean returned to Armstrong and said: ‘I just heard the funniest story!’ Armstrong said: ‘What?’

‘I heard that you bailed out of the LLRV an hour ago.’

‘Yeah, I did,’ replied Armstrong. ‘I lost control and had to bail out of the darn thing.’

Bean later recalled: ‘I can’t think of another person, let alone another astronaut, who would have just gone back to his office after ejecting a fraction of a second before getting killed.’

So no doubt … Armstrong was made of the right stuff for space travel!

Bottom line: On May 6, 1968 – more than a year before his famous first moonwalk – Neil Armstrong narrowly escaped disaster during a training accident.

Read more: Artemis 2: Return to the moon

Read more: 4 astronauts win Congressional Gold Medals

The post Today in science: Neil Armstrong’s close call first appeared on EarthSky.

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Jan Oort: Father of the Oort Cloud

Jan Hendrick Oort was born on today’s date – April 28, 1900 – in Franeker, Netherlands. We know his name today because he theorized the existence of the Oort Cloud, a vast comet cloud in the outermost reaches of our Solar System.

As early as 1932, Oort also became one of the first to use the term dark matter.

And, when it came to expertise about our home galaxy, the Milky Way, few astronomers in the 20th century were more knowledgeable than Jan Oort.

Jan Oort and the Oort Cloud

1950 was a key year for Oort. That was the year he proposed the theory of the Oort Cloud.

The Oort Cloud is also known as the Öpik-Oort Cloud in honor of Ernst Öpik, an Estonian astronomer. Öpik had independently postulated the existence of a cloud of comets encircling our Solar System in 1932.

The theory of this comet reservoir stemmed from astronomers’ observations. They noticed that two types of comets travel into the inner Solar System to round the sun that binds them in orbit. Some have relatively short orbital periods, on the order of about 200 years or less. And some comets require much longer, thousands of years, to orbit the sun once.

But where do these comets come from? Oort proposed a reservoir of comets at the outer limits of our Solar System. He said that long-period comets are sometimes knocked from their very distant orbits (perhaps by passing stars) to orbits that bring them near our sun.

If it exists, this cloud of comets – the Oort Cloud – contains material leftover from the formation of our Solar System, 4.5 billion years ago. The comets within it lie as close as about 2,000 times up to about 100,000 times the Earth-sun distance. That’s a distance of up to 93 trillion miles (150 trillion km) away.

The Oort Cloud of comets is not an observed fact. It’s still a theory. But it’s a well-accepted theory by astronomers that has stood the test of time. And it’s thought to explain the origin of long-period comets such as Comet Hale-Bopp.

Jan Oort solved the comet puzzle

Prior to Oort’s work on the Oort Cloud, astronomers wondered for hundreds of years (or thousands of years, if you count history’s earliest watchers of the skies) where comets originate. Astronomers in the 20th century knew that comets collide with other celestial bodies. They knew comets vaporize when they pass too near the sun. And sometimes those close encounters eject them from our Solar System.

And yet there are always new comets coming to our part of the Solar System. Why? Where do they come from?

The Oort Cloud answers this paradox of comets that seem to appear out of nowhere.

In school, he followed his passions

Oort was one of five children. His father, Abraham Hendrikus Oort, was a psychiatrist. Oort’s parents always encouraged him to follow his passions. And so he decided to study physics at the University of Groningen in 1917.

Attending the lectures of astronomer Jacobus Kapteyn was a turning point for Oort. In fact, Kapteyn’s research greatly inspired him and he switched to studying astronomy.

Later, in 1924, Leiden Observatory welcomed Oort, where he began studying high-velocity stars. Two years later, he defended his doctoral thesis on that subject. This was, additionally, four years after the death of his friend and mentor, Professor Kapteyn.

Jan Oort’s early work

In 1926, astronomer Bertil Lindblad explained the stellar motion properties studied by Kapteyn to be the result of the rotation of the Milky Way. He explained it by proposing that stars closer to the center of the galaxy revolve around the galaxy’s center faster than stars farther away from the center. Subsequently, Jan Oort successfully proved and modified Lindblad’s theory in 1927 after observing the velocities of many stars.

During Oort’s studies of star motions in 1932, he noticed that many stars move faster than expected, given their location within the Milky Way. With this in mind, he then used the term dark matter – not as we use it today – but in the sense of ordinary stars that are either dim (or dark) or hidden from us behind other stars.

Oort continued developing the Lindblad theory. It eventually came to be known as the Lindblad-Oort theory because of his contributions.

Later, Oort became a professor at the University of Leiden in 1935. Among other major accomplishments, the young professor determined that our sun is some 26,000 light-years from the center of our Milky Way galaxy. This is still the number we use today. He also calculated that the sun orbits around the center of the galaxy once every 225 million years.

In 1945, the Observatory of Leiden appointed Oort as their Director.

He maintained this position until 1970.

Oort died in 1992, at 92 years old. But his contributions to astronomy live on.

Bottom line: Dutch astronomer Jan Oort was born on April 28, 1900. He visualized a vast reservoir of icy comets on the outskirts of our Solar System, which now bears his name.

Read more: Could there be a captured planet hiding in the Oort Cloud?

The post Jan Oort birthday and discovery of the Oort Cloud first appeared on EarthSky.

Why do tinamou birds lay such colorful eggs?

Most birds of a similar species lay eggs of a similar color. That’s why the myriad egg colors of tinamou birds have long fascinated scientists. The eggs range from brilliant pinks and blues to rich purples and greens. So similar species … same habitat pressures … but different egg colors? Scientists think the diverse colors might be a social mating signal. And the latest research shows that various colors might help these ground-nesting birds differentiate their eggs from those of closely related species.

A team of researchers published their findings on Tinamou egg color in the peer-reviewed journal Evolution in May of 2023.

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What determines egg colors?

Scientists have a decent grasp on the broad factors that influence what color eggs a bird will have. These factors include nesting location and habitat, competition and predation by other species, and mating and incubation cues. Ground-nesting birds, such as killdeers and piping plovers, typically lay pale, speckled eggs that provide camouflage from predators. Meanwhile, birds that are cavity nesters, such as red-bellied woodpeckers and barred owls, lay white eggs. That’s because color would have little benefit in the dark and not be worth the energy investment. Then there are birds that lay brightly colored eggs, such as American robins. The robin’s-egg-blue pigment – or biliverdin – is thought to protect the developing embryo from harmful ultraviolet light.

Tinamou birds, which are native to Mexico, Central America and South America, use an assortment of vibrant egg colors. These colors may seem perplexing at first glance. Because these birds are ground nesters, we might expect cryptic (camouflaging) egg coloration to fool predators. But tinamou birds have a well-camouflaged mottled plumage, and they sit on the nests, guarding and incubating the eggs. Thus, the eggs are not readily visible to predators. So other evolutionary driving forces must be at play.

Tinamou egg color as a mating cue

The hypothesis proposed by the team of scientists – Qin Li, Dahong Chen and Silu Wang – in the 2023 study is that egg color serves as a mating signal that contributes to tinamou speciation, which is the process by which new species are formed. They collected data on egg color of 32 tinamou species, using both community science databases and museum collections.

The findings showed that divergent egg colors were more common among species living in the same ecoregions.

Their conclusion was that egg colors evolved partly to help species recognize each other and avoid mating mistakes in areas where similar species live. In the wild, a female would see eggs already in a nest when she approaches a male to mate. The color of the eggs help her determine which species the nest belongs to. Thus, she can decide whether or not to lay eggs with that male and avoid breeding with the wrong species.

In tinamou birds, the females mate with multiple males, and it is the male (not the female) that sits on the nest to incubate the eggs. The nests may contain eggs from multiple females of the same species but not eggs from different species. Possibly, the egg colors could also serve as a cue to the male to incubate only those eggs from his species.

A theory that extends back to Darwin

Tinamou birds appear to be displaying a phenomenon that biologists call character displacement. In character displacement, species living in the same habitat evolve to have different traits to avoid competition. The classic example of character displacement is Darwin’s beloved Galapagos finches. They evolved to have divergent beak shapes, allowing each species to specialize in eating different types of seeds.

Additional reasons for varying egg colors

There might not be only one reason for why tinamou birds lay various colored eggs. Besides helping females find the nests of their own species, predation could still play a role.

Evolutionary biologist Patricia Brennan conducted an earlier study in which she proposed that tinamou egg color may be a signal to other female birds promoting synchronous laying. The idea is that if multiple females can find a nest easily because of the colorful eggs, they may be compelled to lay their eggs at the same time in the same nest as a form of communal nesting. Then, at least some of the eggs would likely survive attacks by predators, such as snakes, foxes and hawks, because there’s safety in numbers. In other words, the sheer number of eggs produced at once increases the odds that at least some will survive.

As egg color expert Dan Ardia, in an interview in the Cornell Laboratory of Ornithology’s Living Bird magazine, said:

There are many competing hypotheses to explain egg coloration and they’re not all mutually exclusive. Pigment function is almost surely a complicated combination of factors depending on the idiosyncrasies of each species.

If you plan to decorate eggs for Easter, you can sneak in some science lessons on how egg color can be used by ground-nesting birds for camouflage and for finding nests. Do you think kids will have a hard time finding camouflaged eggs? EarthSky would love to see science-themed Easter egg photos. Submit them to us!

Bottom line: Why do tinamou birds lay such colorful eggs? Scientists think the many egg colors evolved in part to help closely related species recognize each other and avoid competition from other species at their nest sites.

Source: Character displacement of egg colors during tinamou speciation

Read more: Wisdom, oldest bird, returns with mate to Midway Atoll!

The post Why do tinamou birds lay such colorful eggs? first appeared on EarthSky.

Michael Peres is a professor of biomedical photographic communications at the Rochester Institute of Technology in New York. He’s also an award-winning photo-educator, author, and science photographer, with work featured by CNN, Time, the Weather Channel, Nikon, and Mashable. EarthSky spoke with him via email in January, 2019, to learn more about how to photograph snowflakes.

How did you get interested in photographing snowflakes?

In the winter of 2003–2004, one of my students visited an exhibition of Wilson Snowflake Bentley photographs on display at the Buffalo Museum and Science Center. Her excitement about trying to photograph snowflakes was contagious and within a short period of time on a wintry day in January, my microscopy class moved our gear outside and we tried.

Little did I know how infectious the experience would be for me personally. Now, more than 15 years later, I am obsessed with the challenge during the long and snowy Rochester, New York, winters. Rochester on average can receive more than 105 inches of snow per season. One could speculate that amount of snow would provide ample subjects and chances to photograph unique and interesting ice crystals.

Some snowflake photos

Snowflakes come in a variety of different shapes

During the course of any winter, a wide variety of crystal types fall. My methods and equipment are focused towards photographing crystals that are 1 to 2 millimeters in size and are dendritic [“tree-like”]. All snowflakes start out as water molecules that form hexagons in the right conditions. These embryonic crystals are called stellar plates. They can be infinitely small, but they grow and add water molecules over time. At some time during their formation, they grow wings and other intricate structures. When this happens they become dendritic flakes. They are my favorite crystals to photograph. It has been my experience that I have the best luck when the air temperatures are between 15 and 25 degrees Fahrenheit (about -10 to -5 degrees Celsius). During the course of a winter, each storm can bring a wide range of crystal types including columns, capped columns, needles, and granular snow to share a few types of crystals that can fall.

What process you use to take a photograph of a snowflake?

My process starts by frequently watching the weather forecasts. My equipment is kept outside in the garage. Photographing ice crystals requires that everything I use be kept below 32 degrees Fahrenheit (0 Celsius). I keep an inventory of glass slides with my microscope, and I use a fiber optic light source. Being a snowflake photographer is much like being a fireman and ready at a moment’s notice when things happen. These events can be at night, in the day, when I am at work, and when I am indisposed or when I am ready. When good crystals fall and I am available, I start my photographing.

I catch crystals that are falling using a baking tray with a piece of black velvet draped over the tray. Velvet is useful for isolating the best crystals but also allows for easy retrieval using a small needle taped to a pencil. Depending on the humidity and air temperatures, there is a natural static electricity in the needle and crystal. It allows me to lift the crystal using the needle because they are attracted to one another giving me a chance to position the crystal onto a clear glass slide. It is possible to photograph the crystals in the tray on the fabric but I prefer the isolation against a lighter background and have the opportunity to light from underneath.

I use a low power simple microscope. Basically, the microscope is a repurposed industrial macro stand. I use a 16- or 25-millimeter macro lens and the camera has a bellows. Attached to the bellows (extension tubes can also be used) is a DSLR camera body without a lens.

Once an interesting crystal has been identified in my catch tray, I move it to a glass slide using the needle on the pencil. The slide is placed onto the microscope’s focusing stage where I can compose and focus the image in the viewfinder of the camera.

I use a fiber optic illuminator with a bifurcated gooseneck light guide that illuminates the crystals. I shine light onto a variety of materials located below the stage to provide contrast and color to the light that is refracted into the crystal used to reveal the crystal’s facets.

What about a macro lens?

Any tips for those of us who have been trying to capture a good snowflake photograph with a macro lens? I for one am wondering if some temperatures are better than others for taking snowflake photos, and how on Earth do I keep my hands warm?

It is possible to photograph snowflakes with a smartphone or DSLR. The features and advantages of each camera are pretty clear. The smartphone has a pretty good sensor but focusing the lens, exposure management, and ability to magnify sometimes 1-millimeter crystals are real obstacles. There are accessory lenses that can be added to the smartphone.

DSLR cameras are significantly better choices for this work and are equipped with a macro lens capable of at least 1:1. Canon sells a 65-millimeter macro lens that can achieve 5:1 magnification. Adding extension tubes or by using a simple bellows, you can increase the image size that the camera system produces. My typical crystals benefit from a 3 to 6x magnification.

I dress warmly for this work wearing many layers including insulated boots. I use gloves with finger holes but because of the delicate nature of focusing a microscope, moving the crystal in small increments, I benefit from more control and feel having nothing on my hands. Because of the adrenaline, I can typically work for up to 30 minutes before my hands cannot tolerate the conditions any longer.

I photograph using a medium aperture such as ƒ/5.6. Diffraction at these image sizes can cause the crystals to become less defined if I use a smaller aperture. Often I photograph wide open and create increased DOF images.

Many thanks to Professor Peres for discussing his snowflake photography with EarthSky. More examples of his work can be viewed on his Instagram account @michael_peres.

See some favorite snowflake photos from the EarthSky Community

If this post inspires you to give snowflake photography a shot, please submit your photos to EarthSky Community Photos! We love seeing and sharing your recent captures of the natural world!

Bottom line: How to take photos of snowflakes with Professor Michael Peres of the Rochester Institute of Technology.

The post How to photograph snowflakes from Michael Peres first appeared on EarthSky.

How many eclipses every year?

There are at least four eclipses every year – two solar and two lunar. Four is a common number of eclipses in a year; for example, the years 2025 and 2026 have four eclipses. But four is also the minimum number. And in 2027, there will be five eclipses. Depending on the year, there can be four eclipses, five eclipses, six eclipses or a maximum of seven eclipses in a single year. It’s extremely rare to have seven eclipses in a calendar year. The last time was 1982 and the next time will be 2038. On the other hand, it’s much less rare to have seven eclipses in a period of 365 days.

Eclipses in 2025
March 14: Total lunar eclipse
March 29: Partial solar eclipse
September 7: Total lunar eclipse
September 21: Partial solar eclipse

Eclipses in 2026
February 17: Annular solar eclipse
March 3: Total lunar eclipse
August 12: Total solar eclipse
August 28: Partial lunar eclipse

Eclipses in 2027
February 20: Penumbral lunar eclipse
February 26: Annular solar eclipse
July 18: Penumbral lunar eclipse
August 2: Total solar eclipse
August 17: Penumbral lunar eclpse

It’s rare to have seven eclipses in a calendar year.

It’s extremely rare for one calendar year to contain seven eclipses. The last time it happened was 1982. Looking ahead, we will have seven eclipses in a calendar year only twice in the 21st century (2001-2100), during the years 2038 and 2094. There are 3 solar/4 lunar eclipses in the year 2038, and 4 solar/3 lunar in the year 2094.

A calendar year of seven eclipses can also feature 5 solar/2 lunar eclipses, but this last happened in the year 1935 and won’t happen again until the year 2206.

Or you could have 2 solar/5 lunar eclipses in one calendar year, but this last happened in the year 1879 and won’t happen again until the year 2132.

Suffice it to say a calendar year with seven eclipses is indeed rare.

It’s not so rare to have seven eclipses in 365 days.

Some might argue that the calendar year is an artificial constraint … and they would be right. What if we shift our focus to a period of 365 days? How often do seven eclipses happen within one-year’s time (365 days)?

Looking at it this way, we find many occurrences of seven eclipses in a period of 365 days. Seven eclipses last occurred in one year’s time from November 13, 2012 to November 3, 2013. It’ll happen next from January 31, 2018 to January 21, 2019.

We list the seven eclipses that take place in a period of one year for the years 2012-13 and 2018-19:

2012 Nov 13 solar eclipse
2012 Nov 28 lunar eclipse
2013 Apr 25 lunar eclipse
2013 May 10 solar eclipse
2013 May 25 lunar eclipse
2013 Oct 18 lunar eclipse
2013 Nov 03 solar eclipse

2018 Jan 31 lunar eclipse
2018 Feb 15 solar eclipse
2018 Jul 13 solar eclipse
2018 Jul 27 lunar eclipse
2018 Aug 11 solar eclipse
2019 Jan 06 solar eclipse
2019 Jan 21 lunar eclipse

Fortnight, lunar month and lunar year.

Note that a lunar eclipse and solar eclipse always take place within one fortnight (approximate two-week period) of one another.

Any year period containing seven eclipses must also have three eclipses within the framework of one lunar month – the time period between successive new moons or full moons.

In other words: whenever three eclipses happen in one lunar month, it’s inevitable that seven eclipses should occur in one lunar year of 12 lunar months (a period of about 354 days).

How often do three eclipses happen in one lunar month?

Any time a lunar month has three eclipses, we automatically know that seven eclipses happen within one-year’s time. We investigate how often this happens by referring to a longer natural unit of time known as the Metonic cycle – a period of precisely 235 lunar months (approximately 19 calendar years).

In our chosen 235-lunar-month (19-year) stretch of time, we start with the solar eclipse of November 13, 2012, and end with the solar eclipse of November 14, 2031. We find that five lunar months contain three eclipses within this particular Metonic cycle (from the new moon of November 13, 2012, to the new moon of November 14, 2031).

Five 3-eclipse lunar months in between Nov 13, 2012 and Nov 14, 2031:

1) 2013: Apr 25 full moon – May 10 new moon – May 25 full moon

2) 2018: Jul 13 new moon – Jul 27 full moon – Aug 11 new moon

3) 2020: Jun 5 full moon – Jun 21 new moon – Jul 5 full moon

4) 2029: Jun 12 new moon – Jun 26 full moon – Jul 11 new moon

5) 2031: May 7 full moon – May 21 new moon – Jun 5 full moon

Read more about the phenomenon of three eclipses in one month

Seven eclipses in one lunar year

Because three eclipses happen within one lunar month, seven eclipses also have to fall in one lunar year of 12 lunar months, a period of about 354 days.

We list the dates for the first and final eclipses of the five 7-eclipse lunar years during the 19-year (235-lunar-month) period from November 13, 2012, to November 14, 2031:

1) Nov 13, 2012 (solar eclipse) to Nov 03, 2013 (solar eclipse)

2) Jan 31, 2018 (lunar eclipse) to Jan 21, 2019 (lunar eclipse)

3) Dec 26, 2019 (solar eclipse) to Dec 14, 2020 (solar eclipse)

4) Dec 31, 2028 (lunar eclipse) to Dec 20, 2029 (lunar eclipse)

5) Nov 25, 2030 (solar eclipse) to Nov 14, 2031 (solar eclipse)

In short, it’s not all that rare to have three eclipses in one lunar month, or seven eclipses in one-year’s time (365 days).

Bottom line: It’s extremely rare to have seven eclipses in a calendar year. The last time was 1982 and the next time will be 2038. On the other hand, it’s much less rare to have seven eclipses in a period of 365 days. If I’ve counted everything up correctly, seven eclipses occur in the period of 365 days a total of 29 times in the 21st century!

Catalog of solar eclipses: 2001-2100

Catalog of lunar eclipses: 2001-2100

The post How often do 7 eclipses occur in 365 days? first appeared on EarthSky.

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To get you in the Halloween spirit for the creepy, ghoulish and grotesque, we present to you animals that have spooky-sounding names: goblin sharks, ghost crabs and vampire bats. Learn how these creatures got their spine-chilling names.

Goblin sharks

The Goblin shark is a rare and unusual looking species that lives in the deep sea. The sharks have long flattened snouts, protrusible jaws and sharp, narrow teeth. Their snouts are covered with numerous jelly-filled pores that act as electroreceptors to help them detect prey in the dark depths of the ocean. When a fish, squid or crustacean — favorite prey of the goblin shark — swims too close, the shark’s jaw snaps outward at a lightning-fast speed to grab the unsuspecting animal. Not to worry, goblin sharks do not pose any threat to humans because of the depths at which they live.

Goblin sharks also look unusual because they are pink in color, which is caused by blood vessels that lie close to the surface of their skin.

Goblin sharks grow to an average size of 10 to 13 feet (3 to 4 meters), but larger individuals have been found, including an 18 to 20 feet (5 to 6 meter) long female that was discovered in the Gulf of Mexico in 2000. They inhabit all of the world’s major oceans.

The name goblin shark comes from a translation of its Japanese name, tenguzame. In Japanese mythology, tengu are beings that have long noses and red faces.

Lunchtime!

Goblin sharks are thought to swim slowly in deep water, waiting for animals to come within striking distance. When their prey appears, they quickly extend their unusual jaws to snap up a meal!

Learn more: https://t.co/z0oNsUBIIA #SpookySeason pic.twitter.com/GWuusosRcf

— Oceana (@oceana) October 27, 2024

Ghost crabs

Ghost crabs are common crabs that live on the sandy shores of tropical and subtropical beaches. They are most active at night and have large eyes located on the tips of stalks, which allows them 360-degree view. Another characteristic of ghost crabs is that one of their claws is larger than the other, although this feature is not as pronounced as it is in their close relative, the fiddler crab.

Ghost crabs dig deep burrows in the sand. This helps them avoid predators and stay cool in the summer and warm in the winter. They periodically emerge from their burrows to feed and wet their gills in seawater. They also enter the ocean on occasion to release eggs.

According to the Encyclopedia of Life, the name ghost crab comes from the crab’s pale color and nocturnal behavior. Their scientific name Ocypode means swift-foot in reference to the fast speed at which they can dash around on the beach. Typically, these crabs move around on four pairs of walking legs, but at high speeds they run using only the first and second pairs.

Ghosts on the beach at Mustang Island SP! Not really. But these are ghost crabs scuttling across the sand.#Halloween2017 pic.twitter.com/7foiCSTHjS

— Texas State Parks (@TPWDparks) October 31, 2017

Vampire bats

Of course, a Halloween science blog about spooky-sounding animal names wouldn’t be complete without mentioning the vampire bat.

Vampire bats range from Central to South America. They feed on the blood of livestock and other forest animals, hence their name. These bats have a short muzzle and razor-sharp teeth, which they use to make a small incision in sleeping prey. They then lap up the blood that flows out of the wound. Their saliva contains special anticoagulants that prevent the blood from clotting. While creepy, the loss of blood does not usually harm the prey.

Vampire bats live in large colonies in dark places such as caves or hollow trees. These bats form strong social bonds. If one bat is starving, other bats will sometimes regurgitate their blood meal to help feed the hungry bat.

The vampire bat is the only parasitic mammal on Earth, & feeds primarily on the blood of cattle. It cuts the flesh with its sharp teeth & laps the blood up with its long tongue.

(Photos: Lamar University) pic.twitter.com/pZ7HI5PJ1l

— Weird Animals (@Weird_AnimaIs) November 19, 2020

Bottom line: Learn more about some spooky-sounding animals and how they got their names.

Read more stories about Halloween and science:

Halloween derived from ancient Celtic cross-quarter day

Bats, a spooky season icon, are our lifeform of the week

Find the Ghoul Star of Perseus

The post Goblin sharks, ghost crabs and vampire bats, oh my! first appeared on EarthSky.

By Mike Taylor of Taylor Photography in Unity, Maine.

Seeing aurora is breathtaking, but what about colors?

While observing the aurora, or northern lights, is a truly awe-inspiring and often breathtaking experience, the images that come out of modern day DSLR cameras may not match what you witness in real life. Or even your cell phone. Especially if you live below about 50 degrees N. latitude, as I do in Unity, Maine.

I’ve photographed many colors in the fantastic northern lights displays. And I’ve been lucky enough to observe many colors: green, purple, yellow, orange, red, magenta and blue. But I never really know what color they are unless I’m looking at my camera’s LCD screen. Or more importantly, viewing these images on my computer.

To my eye, at my latitude, the aurora is typically low on the horizon, and it tends to come in shades of grey. With only a small amount of color, as in the photo above.

Latitude makes a huge difference in aurora

I’ve heard from folks who have visited or lived in areas such as Alaska, Norway or higher northerly latitudes. Where they live, the aurora is usually overhead, not on the horizon. So, the colors of an aurora are easily seen with the unaided eye.

Also, I made the attached graphic (below) to show what I mean. Because these three photographs exemplify the most impressive aurora displays I’ve seen. The skies in the top row of images are de-saturated by color (green, yellow, red, magenta, purple, blue) to show what I saw with my eyes.

A bit of green has been retained on the horizons and just a bit of the color that I remember seeing above that: red, violet and red respectively.

Camera settings for aurora

I generally set the white balance on my camera at Kelvin 3450 to 3570 when shooting the features of the night sky. But I will also take a few frames with it set on auto to see what colors the camera thinks it should be capturing. Most times I end up going with the Kelvin setting, which is a little bit on the cool/blue side of the spectrum.

The EXIF data for these shots are K-3450, K-3570 and K-3570 respectively. I process all my photos through Lightroom 4 & Photoshop CS5 and I certainly have an “artist’s view” when bringing an image to life. However, when it comes to these strong aurora scenes, the colors have not been saturated very much because Mother Nature did that work beautifully.

Seeing dancing lights and spikes

I saw “dancing lights” in the sky, spiking straight up starting around 100 feet (30 meters) off the ground. They waved a bit like curtains but stayed in basically the same area. They seemed to be kind of a blur though, and the “spikes” were not very defined. There was definitely a green hue on the horizon and a bit of red color above that. But I didn’t see the crazy red & magenta colors that my camera recorded. I saw what appeared to be white/grey “curtains” dancing along the black sky.

I didn’t see much of anything but I set up, started shooting and immediately saw green on the horizon on my camera screen. I set the camera to shoot 30 second exposures for an hour with just a few seconds in between. So, I could quickly review the scenes on the LCD screen as my camera snapped away.

Within 10 minutes or so, I saw sharp spikes or columns shooting up and slowly moving across the sky. To my eye they appeared to be a light violet/purple color enough that I posted a status update to Facebook at 2:24 am. I said:

You know the aurora is cranked up when you can see the purple spikes with your naked eye.

When the display died down, I quickly looked through my images but I didn’t really know the spikes were blue until I viewed them on my computer.

Incredible oval, perfect arc and tall spikes. Oh my!

The most impressive oval I’ve ever seen, a perfect arc which covered the Northern sky’s horizon. The tallest and most crisp “spikes” I’ve witnessed, reaching all the way to the stars. Again, I saw definite green around the oval at the horizon but the spikes themselves were white/grey. And not the intense red that my camera captured.

Aurora displays ebb and flow, constantly changing

The intensity of the aurora always ebbs and flows, sometimes it is quite strong and other times it is mild. If you can see a simple glow or swirling lights on the horizon and/or “spikes” shooting into the sky that look like spotlights and/or “curtains” of light, pay attention and/or be patient. The display can last just a few minutes, a half hour or longer. Most of the intense shows I have witnessed in central and northern Maine have lasted around half an hour.

Why are the colors of the aurora so elusive? The simple answer is that human eyes have difficulty perceiving the relatively “faint” colors of the aurora at night. Our eyes have cones and rods. The cones work mainly during the day and the rods work mainly at night.

Jerry Lodriguss at astropix.com wrote:

Humans use two different kinds of cells in their eyes to sense light. Cone cells, concentrated in the fovea in the central area of vision, are high resolution and detect color in bright light. These are the main cells we use for vision in the daytime. Rod cells, concentrated in the periphery around the outside of the fovea, can detect much fainter light at night, but only see in black and white and shades of gray. [The aurora or northern lights] only appear to us in shades of gray because the light is too faint to be sensed by our color-detecting cone cells.

What you see versus what cameras capture

Thus, the human eye views the northern lights generally in faint colors and as shades of grey and white. While DSLR camera sensors don’t have the same limitation as our eyes. Couple that fact with long exposure times and high ISO settings of modern cameras, and it’s quite evident that the camera sensor has a much higher dynamic range of vision in the dark than we do.

By the way, the same thing is true regarding the Milky Way and night photography in general.

Feel free to share this post if you dig it and if you’ve read all the way down to here, I offer you a sincere thanks. I hope you found this information useful!

Cheers!

Images and article via Mike Taylor and reprinted with permission.

Bottom line: A camera records more vivid colors in an aurora than you see with the unaided eye. Either way, they are an awesome sight!

Taylor Photography is an imaging studio based in a 19th century farmhouse in central Maine. I have been a scenic & nature photographer and a studio photographer for over 20 years. My recent work in landscape astrophotography has been featured on Space.com, the International Dark Sky Association, Earthsky.org, Spaceweather.com, Accuweather Astronomy and multiple other science pages. I offer night photography & post-processing workshops and I am available for studio/product, architectural and website development photography services. Visit me at:

Taylor Photography

Facebook: https://www.facebook.com/miketaylorphoto

Pinterest: https://pinterest.com/taylorphoto1

Blue aurora, star trails, in Unity, Maine

Also check out EarthSky’s current solar activity

The post Will you see colors in aurora? Or do you need a camera? first appeared on EarthSky.

If your eyes could detect gamma rays, you would see brilliant bursts of light in the sky about once per day. The flashes would be so brilliant, they would momentarily outshine everything, including the sun. These gamma ray bursts (GRBs) are the most powerful singular events in the universe. In fact, they can release more energy in a few seconds than the sun will emit in its lifetime. They’re thought to be messages from the beginning of time when the most massive stars in existence violently collapsed. Or they’re from collisions of neutron stars and black holes.

Types of gamma-ray bursts

There are two main categories of gamma-ray bursts. According to NASA:

GRBs come in two forms, long and short. The initial flash of long GRBs can last two seconds to hundreds of seconds long, while the initial flash of short GRBs lasts less than two seconds. Short GRBs are associated with the collision of two compact objects like two neutron stars or a neutron star and a black hole. They collide to form a kilonova and have a spectrum dominated by more energetic (“harder”) gamma rays. Long GRBs stem from the explosive, supernova deaths of massive stars at least 10 times the mass of our Sun and have a spectrum dominated by relatively less energetic (“softer”) gamma rays.

In both classes, the newly born black hole beams jets in opposite directions. The jets, made of particles accelerated to near the speed of light, pierce through and eventually interact with the surrounding material, emitting gamma rays when they do.

Gamma ray bursts discovered by accident

GRBs were discovered by accident while looking for a very different kind of electromagnetic outburst. In the early 1970s, military satellites monitored our planet for violations of the Nuclear Test Ban Treaty. Rogue nuclear tests would show up as gamma ray flashes coming up from the ground. Indeed, flashes were detected, but they did not originate on Earth.

Hundreds of bursts were recorded for decades but their nature remained a mystery. Because gamma rays are very difficult to focus, it was impossible to pinpoint their locations on the sky. Also, their ephemeral nature made them maddeningly tricky to investigate. By the time a telescope could be pointed in the direction of a flash, it was too late.

Some researchers speculated they might be engineered by advanced civilizations.

Observations of gamma ray bursts with advanced telescopes

With the advent of more advanced telescopes, GRBs started to reveal more about themselves in the 1990s. They were definitely not local. GRBs in the Milky Way would have been seen mostly in the thin plane of our Milky Way galaxy. The Compton Gamma Ray Observatory found that they came from all over the sky. Astronomers realized they must be extragalactic. Better telescopes which quickly pinpointed the precise location of a GRB led to the detection of faint afterglows all across the electromagnetic spectrum. In every case, the GRB came from the same direction as a very distant galaxy. These galaxies tended to be young, active stellar nurseries, the perfect place to build very massive stars.

The afterglow light revealed a lot more. By measuring how much the light had been redshifted by the expansion of the universe, astronomers could estimate their distances. And they were most definitely not local. The light from GRBs had been traveling for over half the age of the universe. They were among the most distant objects ever seen. But to be so far away and still be the brightest thing in the sky meant an unimaginable amount of energy had to be producing these flashes.

In fact, the amount of energy needed was equivalent to converting all the mass in the sun to pure radiation in a matter of seconds. Not even a supernova can do that. You would need something even more powerful: a hypernova.

More recent observations have been made with NASA’s Fermi Gamma-ray Space Telescope and NASA’s Neil Gehrels Swift Observatory.

Powerful explosions create jets of gamma rays

An extraordinarly massive dying star can collapse its core into a black hole without triggering a supernova. With the sudden removal of the stellar core, the upper layers of the star come crashing down to fill in the cavity. If the star is spinning rapidly, the infalling material is whipped up into a swirling frenzy. A disk forms deep inside the star. In the ensuing vortex, superheated plasma is ensnared by highly twisted magnetic fields. Like an electromagnetic cannon, jets of gas blast through the poles of the star and erupt into space. The tunnel through the star forces the plasma streams into narrow cones, tightly focusing the energy of the collapse.

How they are visible from Earth

If one of these jets is pointed towards Earth, we see it as a brilliant flash of gamma ray light that fades after only a few seconds.

So it seems that most gamma ray bursts originate in a narrow beam of intense radiation released during a supernova or hypernova as a rapidly rotating, high-mass star collapses to form a neutron star, quark star, or black hole.

Meanwhile, subclass of gamma ray bursts (the “short” bursts) – events with a duration of less than about two seconds – appear to originate from a different process: the merger of binary neutron stars (or a neutron star and a black hole).

GRBs hold many records in astronomy. The most distant object seen by astronomers is a burst whose light has been traveling for nearly the age of the universe. The stellar behemoth that produced it exploded shortly after the age of the first stars! Another GRB is the most energetic event known: 2.5 million times brighter than the brightest supernova. And supernovae, for the record, typically outshine entire galaxies. For 30 seconds in 2008, it was the most distant object visible to the naked eye – 7.5 billion light-years.

Are gamma ray bursts dangerous to Earth?

Luckily, all the GRBs have been at very safe distances from Earth. The closest, detected in 2003, is still over a billion light-years away. Were a GRB to go off in our own galaxy, though, it could be troubling for humanity. A nearby GRB pointed right at Earth could quite possibly trigger a mass extinction or even sterilize the planet.

Fortunately, GRBs are incredibly rare. Any given galaxy may only see one every few million years. Still, that’s enough time for Earth to have been blasted more than once in its long history. There is, in fact, evidence to suggest that one extinction event, 450 million years ago, may have been the result of a nearby GRB.

Cosmology and gamma ray bursts

Gamma ray bursts call to us from across the cosmos. They are echoes from the beginning of time, beacons from the violent implosion of stellar giants. And though the night sky is routinely bathed in their glow, we did not know they were there until very recently. Our eyes can only detect a tiny sliver of all the information racing through the cosmos. Without advanced detectors and telescopes, much of the universe would remain forever hidden. What else has been hiding from humanity through all our history? And what new secrets will we uncover tomorrow?

Bottom line: Gamma ray bursts are caused by a narrow beam of intense radiation coming from the poles of an exploding star. They appear in our sky when the jet from the rapidly rotating star points toward Earth.

The post What are gamma ray bursts? first appeared on EarthSky.

Friday the 13th occurs twice in 2023

Today is October 13, 2023, and it’s a Friday. And it’s the last of two Friday the 13ths in 2023. There was one in January. Does that mean 2023 is super unlucky? No. Any calendar year has at least one – but no more than three – Friday the 13ths. The last time we had only one Friday the 13th in a calendar year was in 2022. And the next time won’t be until 2025. Are you scared of Friday the 13th? Or has it just got a bad rap? It’s really just a feature of our Gregorian calendar, and a pretty common one at that.

We last had three Friday the 13ths in 2015, in February, March and November. We’ll have three again in 2026.

There’s a name for having an irrational fear of Friday the 13th: friggatriskaidekaphobia. Not that we at EarthSky suffer from this fear … but, gosh darn, this year’s first Friday the 13th was on January 13, 2023, and it happened exactly 39 weeks (3 x 13 weeks) before the second Friday the 13th in October 2023. And that’s not the end of it.

Next year, in 2024 (which also has two Friday the 13ths), the first of the two comes on September 13, 2024, exactly 13 weeks before the second Friday the 13th in December 2024. Then the sole Friday the 13th of 2025 falls on June 13, 2025, exactly 26 weeks (2 x 13 weeks) after the December 2024 Friday the 13th.

Yikes, that’s quite a few of coincidences involving the number 13 … though we could cite many more!

The 2024 lunar calendars are here! Best Christmas gifts in the universe! Check ’em out here.

Why do some people fear Friday the 13th?

Are all these 13’s a scary coincidence or is it super unlucky? Neither. It’s just a quirk of our calendar, as you’ll see as you keep reading.

The fact is that, according to folklorists, there’s no written evidence that Friday the 13th was considered unlucky before the 19th century. The earliest known documented reference in English appears to be in Henry Sutherland Edwards’ 1869 biography of the composer Gioacchino Rossini, who died on a Friday the 13th.

Unlucky? I don't think so. The 13th is more likely to be a Friday than any other day of the week! https://t.co/aKfOawx8w7 pic.twitter.com/Che7xmZJrv

— Nick Berry (@DataGenetics) October 13, 2017

Has Friday the 13th got a bad rap?

Friday has always gotten a bad rap regardless of its number in the month. Even in the Middle Ages, people would not marry – or set out on a journey – on a Friday.

There are also some links between Christianity and an ill association with either Fridays or the number 13. Jesus was said to be crucified on a Friday. Seating 13 people at a table would supposedly bring bad luck because Judas Iscariot, the disciple who betrayed Jesus, was the 13th guest at the Last Supper. Meanwhile, our word for Friday comes from Frigga, an ancient Norse goddess of marriage and fertility. Christians called Frigga a witch and Friday the witches’ Sabbath.

In modern times, the slasher-movie franchise Friday the 13th has helped keep friggatriskaidekaphobia alive.

Everything We Know About The New #FridayThe13th Show ‘Crystal Lake’ So Farhttps://t.co/TGCVDkaD6y

— Friday The 13th: The Franchise (@F13thFranchise) November 24, 2022

In 2023, blame a common year starting on Sunday.

Whenever a common year of 365 days starts on a Sunday, it’s inevitable that the months of January and October will start on a Sunday. And any month starting on a Sunday always has a Friday the 13th. So this year, in 2023, both January and October have a Friday the 13th.

The last time a common year started on a Sunday was 6 years ago, in the year 2017. Before that, it was in the year 2006. This marked the first time in the 21st century (2001 to 2100) that New Year’s Day started on a Sunday.

Some of you may wonder if there’s some formula that governs how this twofold Friday the 13th drama repeats itself. The answer is a definite yes. Keep in mind that this January-October Friday the 13th year can only happen in a common year of 365 days, and when January 1 falls on a Sunday.

Any calendar year that happens three years after a leap year will recur in cycles of 11, 22 and 28 years. Therefore, if our twofold Friday the 13th year comes three years after a leap year, as it does in 2023, the days and dates will match up again in 11, 22 and 28 years. So the years 2034, 2045 and 2051 will all harbor January and October Friday the 13ths:

2023 + 11 = 2034
2023 + 22 = 2045
2023 + 28 = 2051

Calendar for 2023

How often does a Friday the 13th happen in January and October?

More often than you might imagine! The first January-October Friday the 13th year in the 21st century (2001 to 2100) occurred in 2006, which is two years after a leap year. Any calendar year happening two years after a leap year will have days and dates matching up again in periods of 11, 17 and 28 years:

2006 + 11 = 2017
2006 + 17 = 2023
2006 + 28 = 2034

Next, we continue the cycle onward to find a grand total of 10 January-October Friday the 13th years for the 21st century (2001 to 2100):

2006, 2017, 2023, 2034, 2045, 2051, 2062, 2073, 2079 and 2090

Because the year 2090 is two years after a leap year, we might be tempted to project the next January-October Friday the 13th to the year 2101:

2090 + 11 = 2101

Looking ahead to 22nd century

Alas, here’s where the Gregorian calendar throws a monkey wrench at us. And by Gregorian calendar rules, century years not equally divisible by 400 (e.g. 2100, 2200, 2300) are not leap years of 366 days – but rather, common years of 365 days. So the suppression of the leap year in 2100 perturbs the cycle, bringing about the first January-October Friday the 13th year of the 22nd century (2101 to 2200) in the year 2102, instead of 2101.

By good fortune, we can pretend that the year 2102 comes two years after a leap year, to project the recurrence of January-October Friday the 13th years in periods of 11, 17 and 28 years.

2102 + 11 = 2113
2102 + 17 = 2119
2102 + 28 = 2130

We continue the cycle onward to find a total of 11 January-October Friday the 13th years for the 22nd century (2100 to 2200):

2102, 2113, 2119, 2130, 2141, 2147, 2158, 2169, 2175, 2186 and 2192

And the 23rd century

In the 23rd century (2201 to 2300), the cycle is perturbed again. The first January-October Friday the 13th year does not fall in 2203 – but rather in 2209, which is one year after a leap year. Any calendar year happening one year after a leap year recurs in 6, 17 and 28 years.

Thus, we find 11 January-October Friday the 13th years for the 23rd century (2201 to 2300):

2209, 2215, 2226, 2237, 2243, 2254, 2265, 2271, 2282, 2293 and 2299

And the 24th century

Then in the 24th century (2301 to 2400), the cycle is again perturbed. The first January-October Friday the 13th year does not come in 2310 – but rather in 2305, or one year after a leap year. That gives 11 January-October Friday the 13th years for the 24th century (2301 to 2400):

2305, 2311, 2322, 2333, 2239, 2350, 2361, 2367, 2378, 2389 and 2395

Because the year 2400 IS a leap year of 366 days, the cycle is NOT perturbed in the following 25th century (2401 to 2500). So we can keep on going to find 10 January-October Friday the 13th years for the 25th century (2401 to 2500).

2406, 2417, 2423, 2434, 2445, 2451, 2462, 2473, 2479 and 2490

Rhyme and reason for the 400-year Friday the 13th cycle.

Because the Gregorian calendar has a 400-year cycle, the January-October Friday the 13th years recur in cycles of 400 years. For example, respective January-October Friday the 13th calendar years are exactly 400 years apart in the 21st and 25th centuries:

21st century (2001 to 2100):

2006, 2017, 2023, 2034, 2045, 2051, 2062, 2073, 2079 and 2090

25th century (2401 to 2500):

2406, 2417, 2423, 2434, 2445, 2451, 2462, 2473, 2479 and 2490

Gregoriana cycle of 372 years.

It appears as though cycles of 372 and 400 years (372 + 28) prevail over the long course of centuries. Take the year 2023, for instance:

2023 + 372 = 2395
2023 + 400 = 2423

The 372-year period is known as the Gregoriana eclipse cycle, which we elaborate about in our post How often does a solar eclipse happen on the March equinox?

As magical as all of this Friday the 13th calendar intrigue appears to be, it’s not supernatural. But it’s entertaining number play, even if it may haunt our uncomprehending minds.

Friday the 13th, by the numbers | @DataGenetics https://t.co/ET7kqCAqY4
Image via: https://t.co/5GcrRV6nC9 pic.twitter.com/r3IuwSmnkz

— VMware Tanzu Data (@VMWareTanzuData) November 13, 2015

Can a leap year start on a Sunday?

Yes, a leap year of 366 days can start on a Sunday. It last occurred in the year 2012 and will next happen in 2040. Any leap year starting on a Sunday has three Friday the 13ths which fall in January, April and July. The days and dates of any leap year match up again in periods of 28 years. So we have only four January-April-July Friday the 13th years in the 21st century (2001 to 2100):

2012, 2040, 2068 and 2096

Bottom line: Scared of Friday the 13th? It’s just a feature of our Gregorian calendar, and a pretty common one at that. And from what we’ve been able to gather, the 400-year cycle displayed by the Gregorian calendar features 688 Friday the 13ths.

2015 had 3 Friday the 13ths. What are the odds?

When does Friday the 13th have a full moon?

The post Happy Friday the 13th: It’s the 2nd one in 2023 first appeared on EarthSky.