Kluge's GeoScience News

Latest Sunrise of the Year

noreply@blogger.com (Steve Kluge) — Tue, 03 Jan 2012 11:00:00 +0000

The latest sunrise of the year will occur on January 5 this year...2 full weeks after the shortest day! The earliest sunset occurred on December 8 even as the days continued to get shorter and on December 21-22 (the Winter Solstice) we experienced the shortest daylight period of the year. Since then the days have been getting longer, even as the sunrise was getting later.

It might seem as if the latest sunrise and earliest sunset should occur on the shortest day, but both the tilt of the earth's axis and it's slightly elliptical orbit work together to speed and slow the sun relative to our clocks, sometimes pushing the daylight period later into the day (as has been happening in the last month), and other times moving the daylight period into the morning in a predictable pattern we call "the equation of time".

The term solstice means sun stops, or sun stands still. Of course the sun is always moving east to west across our sky, but from late November through mid January, the sun is nearly as far south as gets (it stops moving further south!) - and that's why we see such uniformity in the length of the day....9 hours 20 minutes on 12/8, 9 hours 13 minutes on the solstice, and 9 hours 20 minutes again on 1/4. It isn't until late February that you'll really notice rapid lengthening of the day.

Earliest Sunset of the Year

noreply@blogger.com (Steve Kluge) — Mon, 05 Dec 2011 12:23:00 +0000

December 8, 2011. For the last few years, I've posted this in early December...12/8 marks the earliest sunset of the year! The daylight period is still getting shorter (people who pay attention to these things know that the shortest day is the Winter Solstice around December 21), but not a lot of people can explain tonight's early sunset. It turns out that the rate at which the Sun travels across the sky is not constant - the tilt of Earth's axis and its elliptical orbit conspire to push the Sun ahead of our clocks, and then slow it down again, twice every year. Astronomers call the difference between time told by the Sun (apparent solar time) and clock time (mean solar time) the "equation of time".(If you're interested, you can get the sunrise and sunset times for your location at the US Naval Observatory site.)
The chart on the left above, called the analemma, combines the equation of time with the position of the Sun relative to the equator. Click it for a larger view, and notice that through most of the fall the Sun has been running ahead of the clock, but in December it began to slow dramatically.
It's the Sun slowing down relative to the clock that's moving the daylight period later into the day even as the days get shorter! The worst of winter is still ahead of us, but at least we'll have a little more evening daylight... (the latest sunrise of the year occurs during the first week of January)
This photo composite was made by Tom Matheson over the course of a year, snapping a picture of the Sun at exactly 8 AM (by the clock) each day. Here is a labeled image of Tom's photo.

(This blog is an edited re-post from December 2009 and 2010)

Cloud Filled Valleys in Pennsylvania

noreply@blogger.com (Steve Kluge) — Wed, 26 Oct 2011 13:23:00 +0000

Nearing the end of a red eye flight from California to New York on 10/17/2011, I was treated to this intriguing view of cloud/fog filled valleys as the Sun rose over the northern reaches of the Valley and Ridge Province of Pennsylvania. Overnight temperatures in the valleys had dropped to the dew point and below the stream water temperature. Under those conditions moisture evaporating from the warmer streams quickly condensed to fill the valleys with fog and clouds, some rising high enough to catch light from the rising sun.

The metar above, covering Sunday 10/16/2011 through Monday 10/17/2011 at Williamsport, PA reveals the cool, saturated, and still air that was in place around sunrise on Monday.

The Great Tohoku Quake of March 2011

noreply@blogger.com (Steve Kluge) — Mon, 28 Mar 2011 02:20:00 +0000

The day after the great M 9.0 Tohoku quake near Honshu, Japan, on 3/11/2011, CNN ran an article with the headline "Quake moved Japan coast 8 feet, shifted Earth's axis" (it was likely based upon this report out of Caltech the day before). The claim seemed too remarkable to be true, and I wrote to a few seismologist/geologist friends for their take on it. A friend at IRIS sent me to the Geospatial Information Authority of Japan, and I searched around for more emerging information.

It turns out that entire island did not move 8 feet, but near the epicenter the movement and deformations of the island and seafloor were even more astounding than the "8 foot" claim.
I've gathered a number of maps, charts, and images pertinent to the quake and put them in a single Google Earth file available here. The links above, and many more, are in the Google Earth file.
Here are some of the truly incredible things that happened during the quake

The northeastern shore of the island near the epicenter moved eastward more than 4m during the quake....yes! GPS measurements reveal it! The western part of the island moved eastward by somewhat less than a meter....So part of northern Japan (near the epicenter) is now some 3+m wider than it was prior to the quake! (turn on the japan-slip overlay in the file I sent). I'm assuming that there was significant compressional stress built up in the island, and the land expanded eastward as that stress was released during the quake.
The motion along the boundary between the subducted Pacific Plate and the overriding Okhotsk Plate* on was on the order of 24m at the epicenter! (turn on the japan-mainshock-slip overlay in the file I sent). Apparently almost all of the motion was accommodated by the overriding plate moving eastward and up, while the Pacific Plate hardly moved. *(The Okhotsk Plate is part of the larger North American Plate).
The upward movement of the plate raised the level of the seafloor just west of the trench an astounding 4.5+m, and created a basin 2+m deep off the shore (turn on the japan-uplift-and-subsidence overlay in the file I sent). The subsidence of the seafloor lowered the island by about 1m along the shore there (which would have the effect of moving the shoreline inland, but not the rocks under it). I don't know this for a fact, but it seems like a 5m rise in the seafloor and a simultaneous lowering of the coastline would have added signficantly to the damage caused by the tsunami.

And here's something I noticed as I looked over these maps. Bring the japan-mainshock-slip overlay to the top of the 3D display by turning it off, and then on again. The dotted isolines are the depth to the interface between the overriding Okhotsk Plate and the subducted Pacific Plate seafloor.

In the Layers panel in the GE sidebar, expand the Gallery folder and turn on Volcanoes.

Now, notice where the volcanoes are relative to the depth of the plate boundary...Seems like the generation of magma that makes it to the surface begins at about 100km depth..... I drew a profile across the area, and collected data to make the annotated chart above.

Twinkling Sirius

noreply@blogger.com (Steve Kluge) — Sat, 15 Jan 2011 09:00:00 +0000

Screenshot from the free planetarium, Stellarium (www.stellarium.org)

If you've watched the night sky much, you've probably noticed how stars seem to twinkle, a phenomenon known as "scintillation". More careful observation may have revealed that the scintillation is more pronounced in stars near the horizon, and that the planets, while appearing star-like, generally don't twinkle even as the stars around them do!

In my recent post regarding the winter hexagon I described how to locate the bright blue-white star Sirius by tracing the line of stars of Orion's belt down and to the left. Sirius is the brightest star in Earth's nighttime sky, at least in part because at 8.6 light years distant it is also one of the nearest stars. For observers in northern latitudes, Sirius arcs across the southern winter sky, rising south of east a few minutes earlier each night, and setting south of west about 9 and a half hours later. By late January Sirius is high in the southern sky by 8 PM (see the image above), and on a clear cold night it puts on a dazzling show, especially if you let your eyes adjust to the dark for a while. The scintillation will be obvious, and if you look closely you'll see that the color of the star changes too - flashing rapidly from red to green to blue and back again. Here's the explanation:

The star itself neither twinkles nor changes color - those visual effects are the result of the passage of the starlight through Earth's atmosphere on the way to your eyes.

Stars, no matter how large they are, are so far away that even with a large earthbound telescope they cannot be resolved into anything more than a single point of light - we can't observe their surfaces or even resolve them into disks. When the single narrow beam of light from a star enters Earth's undulating atmosphere, it is bent, or refracted, from its perfectly straight path - first directly into your eyes (making it appear bright) and in the next instant away from your eyes (dimming it) - essentially making it twinkle.

The bright white light coming from Sirius is really a combination of all the colors of the rainbow, and atmospheric refraction can split that light into its rainbow components in the same way a prism does. The scintillation then directs and redirects the various colors to your eyes:

The scintillation and refraction of Sirius' starlight cause it to twinkle in various colors

The result is a scintillating, color changing star! The reason the scintillation is more pronounced near the horizon is that the incoming starlight must pass through more atmosphere before it reaches your eyes. Light from the planets also scintillates, and while they may appear star-like in the sky, unlike stars they actually have some dimension to the them (we can see their disk-like shape). We receive light from many points on the surface of the disk and the scintillation of those multiple beams tends to cancel out the twinkling effect - the planet shines steadily in the sky. Check out twinkling Sirius and steady Jupiter during the moonless evenings of late January (2011).

The Winter Hexagon and a Lunar Eclipse

noreply@blogger.com (Steve Kluge) — Wed, 15 Dec 2010 03:00:00 +0000

This image is edited from a Stellarium screenshot. Stellarium is an excellent, free, planetarium program. Click for a larger view.

"Orion's Belt", part of the constellation Orion, is a well known and easily recognized asterism in the northern hemisphere's winter sky (between Betelgeuse and Rigel on the image above). Six bright stars surround Orion's belt forming the Winter Hexagon, outlined in the image above. Those stars are easy to find on a dark, clear night - follow the line formed by Orion's Belt to the left to locate the bright and twinkling star Sirius, drop down perpendicular to the Belt to find blue-white Rigel, follow the belt to the left to spot Aldebaran (the orange "eye of the bull" in the constellation Taurus). Look up from Aldebaran to find Capella (in the constellation Auriga), to the left of Capella find Pollux (the brighter of the twins of Gemini), and the sixth star of the hexagon is Procyon, below Pollux on the way back to Sirius.
The Moon passes through the Winter Hexagon each month in its orbit around the Earth, and this month it will be December's Full Moon passing through on the night of 12/20 - 21/2010. Go out and take a look on Monday, 12/20 - the brightest stars you'll see around the Moon are the stars of the Winter Hexagon. And on this particular night, the position of the Moon marks an important position in the sky...the exact spot the Sun will be on June 21, six months from now - a place in the sky called the "summer solstice". Tonight's Full Moon will trace the same path across the sky that the summer sun will follow in June! On this night, too, the Sun is directly opposite the Moon on the other side of the Earth:

This image is a composite of Google Earth images cobbled together to show the relative locations of the Moon, Earth and Sun during the upcoming eclipse. Click for a larger view

At around 1:30 AM (EST) the Moon will enter the darkest part of the Earth's shadow (called the umbra). For the next 3 1/2 hours, the Moon will move from right to left through the Earth's shadow, darkened to an orangey-red in the dim light of the Earth's shadow.
If you're willing to stay up, or wake up around 2 AM (EST) on the morning of Tuesdsay 12/21, you can view the last lunar eclipse of 2010. Worth it, I say!
Here are some photos I took during the lunar eclipse of February, 2008. That eclipse happened in the constellation of Leo and some of my photos included images of the bright star Regulus (Leo's "heart") and the planet Saturn with its rings tipped toward us.

The Geminid Meteor Shower

noreply@blogger.com (Steve Kluge) — Sun, 12 Dec 2010 14:50:00 +0000

(photo courtesy NASA.gov)

This Monday night (well, actually early Tuesday morning- the night of 12/13- 12/14) marks the peak of the 2010 Geminid Meteor Shower, an event that occurs every year as the Earth passes through the debris stream associated with asteroid 3200 Phaethon (see this NASA article for more on Phaethon and its debris stream). This year's show is expected to produce up to 120 meteors per hour in the pre-dawn hours of Tuesday, 12/14 - that's a good show! To view the shower, bundle up and head out any time after midnight (the later the better). You don't have to look in any particular direction, just up - if you can find a dark place to sit back and look up at the whole sky, that will work the best. The meteors can appear anywhere in the sky, but if you trace their paths backward you'll find that they all seem to come from the constellation Gemini (face to the SSW and look up almost overhead...those 2 bright stars up there are Castor and Pollux, the Gemini twins). Here are some general hints for successful meteor viewing.
Cloudy weather is predicted in the northeast, so check the latest radar before you set your alarm Monday night....

Earliest Sunset of the Year!

noreply@blogger.com (Steve Kluge) — Thu, 09 Dec 2010 20:31:00 +0000

December 8, 2010. Well, we've made it again!. Tonight is the earliest sunset of the year! The daylight period is still getting shorter (most folks know that shortest day is the Winter Solstice around December 21), but not a lot of people can explain tonight's early sunset. It turns out that the rate at which the Sun travels across the sky is not constant - the tilt of Earth's axis and its elliptical orbit conspire to push the Sun ahead of our clocks, and then slow it down again, twice every year. Astronomers call the difference between time told by the Sun (apparent solar time) and clock time (mean solar time) the "equation of time".(If you're interested, you can get the sunrise and sunset times for your location at the US Naval Observatory site.)
The chart on the left above, called the analemma, combines the equation of time with the position of the Sun relative to the equator. Click it for a larger view, and notice that through most of the fall the Sun has been running ahead of the clock, but in December it began to slow dramatically.
It's the Sun slowing down relative to the clock that's moving the daylight period later into the day even as the days get shorter! (the latest sunrise of the year occurs during the first week of January)
This photo composite was made by Tom Matheson over the course of a year, snapping a picture of the Sun at exactly 8 AM (by the clock) each day. Here is a labeled image of Tom's photo.

(This blog is an edited re-post from December 2009)

The Days Are Getting Longer, Fast!

noreply@blogger.com (Steve Kluge) — Tue, 16 Mar 2010 10:20:00 +0000

Even the most casual observers have noticed that the days are getting longer fast at this time of year. The table to the right is derived from sun rise and set data provided by the US Naval Observatory for White Plains, NY, and a quick study of the data reveals why.

On 3/25, the Sun will rise 17 minutes earlier and set 10 minutes later than it did on 3/15 - a gain of 27 minutes of daylight in just 10 days!

While the daylight period has been getting longer since the winter solstice on December 21, a look at the Sun rise and set times for late December reveal why those long winter nights seem to drag on for so long...10 days after the solstice, the sun was rising 3 minutes later and setting 6 minutes later, for a hardly noticeable gain of only 3 minutes of daylight!

The geometry of the Sun's path among the stars is responsible for the variability of the change of the length of daylight. The length of daylight changes quickly around the equinoxes in March and September, and very little around the solstices in June and December.

Notice too that the gains are not symmetrical around noon - in March the morning gains are almost twice as great as the evening gains, and in December the sun rises later each day even as the days get longer - the lengthening is all in the evening!

This is because the Sun speeds up and slows down relative to the clock (which is in sync with the average time the sun takes to cross the sky). In the spring the Sun is "speeding up" relative to the clock while in December the Sun slows so dramatically that sunrise lags behind the clock even as the days get longer! This is all a result of both the changing velocity and axial tilt of the Earth in its orbit around the Sun (see this analemma discussion for more information on the relationship between solar and clock time).

12 Hours of Daylight!

noreply@blogger.com (Steve Kluge) — Tue, 16 Mar 2010 09:00:00 +0000

The Sun will cross the equator shortly after noon EST on 3/20 this year at a place in the sky we call the equinox, but tomorrow - 3/17 - is the day when we'll have 12 hours of daylight and 12 hours of night...Learn why here.

The image above was made in Stellarium, and shows the location of the Sun as viewed from White Plains, NY at the moment of the 2010 vernal equinox on 3/20. The blue line is the celestial equator, and the red line is the annual path of the Sun among the stars (it moves to the left, or east, among the stars at about 1 degree/day due to Earth's revolution around the Sun). The atmosphere has been "turned off" to reveal the background stars and planets.

It's Still Cold...But the Sun's Coming Back!

noreply@blogger.com (Steve Kluge) — Fri, 19 Feb 2010 20:53:00 +0000

Even though winter drags on, I'm always intrigued by the changes in the Sun that foretell the coming of Spring. You may have noticed that the days are getting longer quickly and that the Sun (when it's not blocked by clouds!) is warmer and more intense than it's been in months. I've had to reset the timers on the lights in my house a few times already, and I've noticed that when my car sits in the sun it warms up inside - a little anyway - even when it's cold outside.
In the weeks before and after the vernal equinox (around 3/21) the Sun's apparent motion among the stars brings it quickly from south to north across the celestial equator. The result is a rapid lengthening of the daylight period, and a noon sun that climbs higher in the sky each day.
The charts below were made with a year's worth of sunrise and sunset data for White Plains, NY provided by the US Naval Observatory.

On the chart above (click it for a larger view), notice that from mid February through most of April, the days lengthen by more than 2.5 minutes a day. And notice too, that the daylight period is long from late May through the the first weeks of August.

The chart below is derived from the same data, and shows the longest and shortest days as well as the earliest and latest sunrises and sunsets of the year.
If you want to play around with the data, it's here in an Excel spreadsheet.

The Oblate Sun

noreply@blogger.com (Steve Kluge) — Wed, 20 Jan 2010 10:58:00 +0000

This shot of the setting sun taken from Seamans Neck Park in Seaford, NY illustrates an interesting atmospheric optical property. Earth's atmosphere causes refraction of the sunlight (and moonlight, and starlight) that passes through it. Near the horizon, refraction will raise an object on the horizon (like a star or the Sun) to an apparent position about 0.5° above the horizon. When the 'bottom' of the Sun is raised more than the 'top', the rising or setting sun can look quite flat! This refraction hastens the apparent rising of the Sun and delays the apparent setting of the Sun, effectively giving us a few more minutes of daylight than we'd have if there was no atmosphere at all. You can read a little more about the effect this refraction has on the length of day here.

Revealing New York City Skyline

noreply@blogger.com (Steve Kluge) — Sun, 10 Jan 2010 15:46:00 +0000

This photograph of the New York City skyline was taken from the top of Bear Mountain in the Hudson Highlands some 40 miles (64 kilometers) due north of the city. It reveals something interesting about the interplay of physical and cultural geography as New York City developed.
Notice how the large, tall buildings are clustered in the Midtown and Wall Street areas while the buildings in "The Village" (Greenwich Village and Chinatown)are smaller and lower. The pattern is not simply a matter of coincidence - it is controlled by the underlying geology of Manhattan Island. The tall, heavy buildings are built where strong, crystalline bedrock is available at the surface to support them. The Village, on the other hand, is underlain by unconsolidated glacial deposits incapable of supporting such massive skyscrapers without extensive and expensive engineering of their foundations.
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The annotated Google Earth screen shot to the left here (south is to the TOP of the image)is a "top view" of what you're seeing in the photograph.
The Midtown - Village - Wall Street pattern is also apparent looking east from the New Jersey Turnpike, and you can read more about the development of NYC at this US Geological Survey page.

New Marble Outcrop in Brookfield, CT

noreply@blogger.com (Steve Kluge) — Sun, 20 Dec 2009 11:00:00 +0000

Generally speaking, I'm not a fan of man-made landscape alteration, but fresh highway roadcuts provide a great unweathered view of the local geology.
A few weeks ago, after years of proposals followed by years of construction, the northern extension of "Super 7" (US route 7) north of Danbury CT finally opened - and the exposures of the Stockbridge Marble along the road are spectacular! The Stockbridge Marble was formed as the rocks of the carbonate bank (limestones deposited off the coast) of ancestral North America were metamorphosed during the Taconic Orogeny ( see blog on 12/2/2009 and the diagram below).

The rocks were further deformed, and actually overtured, in the subsequent Acadian Orogeny. The extent of those deformations are evident in the complex folds pictured here.
Carbonate rocks, including marbles, generally weather faster than silicate rocks, and in SW Connecticut and SE New York many of the regional valleys are underlain by less resistant marbles. Along route 7 between Danbury and New Milford the Stockbridge Marble underlies the Still River valley, and is bounded by harder rocks on either side of the valley. The same rock underlies the Saw Mill River valley in New York where is known as the Inwood Marble (there's a "Marble Avenue" exit on the Saw Mill River Parkway in Pleasantville/Thornwood, and the Shop Rite plaza in Thornwood is built on an old marble quarry there - great outcrops of snowy white "snowflake" marble are still visible on the quarry walls behind the stores, but they're weathering fast!).
Riders of the Hudson Metro North commuter rail can get a good look at the Inwood Marble at the Marbledale stop on the way into Manhattan.

Earliest Sunset of the Year

noreply@blogger.com (Steve Kluge) — Tue, 08 Dec 2009 11:00:00 +0000

Well, we've made it. Tonight is the earliest sunset of the year!
The daylight period is still getting shorter (most folks know that shortest day is the Winter Solstice around December 21), but not a lot of people can explain tonight's early sunset. It turns out that the rate at which the Sun travels across the sky is not constant - the tilt of Earth's axis and its elliptical orbit conspire to push the Sun ahead of our clocks, and then slow it down again, twice every year. Astronomers call the difference between time told by the Sun (apparent solar time) and clock time (mean solar time) the "equation of time".(If you're interested, you can get the sunrise and sunset times for your location at the US Naval Observatory site.)
The chart on the left above, called the analemma, combines the equation of time with the position of the Sun relative to the equator. Click it for a larger view, and notice that through most of the fall the Sun has been running ahead of the clock, but in December it began to slow dramatically.
It's the Sun slowing down relative to the clock that's moving the daylight period later into the day even as the days get shorter!
This photo composite was made by Tom Matheson over the course of a year, snapping a picture of the Sun at exactly 8 AM (by the clock) each day. Here is a labeled image of Tom's photo.

(This blog isan edited re-post from December 2008)

Rocks on the Shore of Lake Champlain Tell an Interesting Story

noreply@blogger.com (Steve Kluge) — Wed, 02 Dec 2009 11:00:00 +0000

An early May paddle on Lake Champlain turned into an interesting geology field trip (for me at least ;-) ) when we passed this rocky shoreline north of Burlington, VT. The rocks here record a significant event in the formation of North America.
To understand what happened here, imagine a deck of cards spread out on a table. Now imagine that you use your arms to bring the cards together into a pile. As the cards slide together some will end up on top of others, and the mass of cards will become shorter in the horizontal direction, but thicker in the vertical direction. In a similar way, colliding crustal plates (“drifting continents”) produce thick masses of earth’s crust pinched between them. Around 440 million years ago, eastern North America was deformed as it collided with volcanic islands to the east as the ocean between North America and Europe was closing (and as the super continent of Pangea was assembling). This event, called the Taconic Orogeny, resulted in the rocks of western New England piling up and forming the Taconic Mts. (which have been reduced from their former grandeur by 400 million years of erosion!)

So what's happening in this photo?

Essentially you're looking at the boundary between 2 of the cards you imagined above. The rocks in the top half of the photo have been thrust westward (to the left) up and over the rocks at the bottom of the image along a "low angle thrust fault" (traced with a red line). It's hard to judge just how far the top rocks have moved relative to the bottom rocks right here, but along a major thrust fault east of here, the displacement is estimated to be on the order of 50 miles! (See this Earth Science Picture of the Day). And you can see that the rocks themselves have been squeezed, too - notice that the shortening and thickening is evident on a very small scale in the deformation of the light colored vein at "A".
You can see more pics of this outcrop, and pics of the entire paddling adventure if you have nothing better to do.
And here's a pretty nice cartoon of the Taconic Orogeny from oldest at the top to present day at the bottom.

Pikes Peak in the Clear

noreply@blogger.com (Steve Kluge) — Tue, 24 Nov 2009 11:07:00 +0000

The morning of June 3, 2009 brought overcast skies and drizzle to Colorado Springs, CO - dampening my hopes of a clear day on a field trip to nearby Pikes Peak (at 14,110 ft, Pikes Peak is one of Colorado's 54 "14ers"). Assured by the folks who run the Pikes Peak Cog Railroad that the summit was clear, we boarded the train for the ride to the top.
It wasn't long before we broke free of the clouds, and soon were way above treeline in a few inches of new snow! From the summit we were able to look back down toward the cloud covered Colorado Springs and the plains to the east, where it remained cloudy and wet for the rest of the day.

Crepuscular Rays

noreply@blogger.com (Steve Kluge) — Tue, 17 Nov 2009 11:00:00 +0000

We've all seen them...my friend Donald calls them "God Lights". The the rays of sunlight that seem to radiate out from the sun through breaks in the clouds are more properly known as "crepuscular rays". We see them because sunlight is scattered by dust and other particles in the atmosphere making the air lit by the sun appear brighter than the air that is in the shadow of the clouds. Though the rays are virtually parallel to each other, perspective causes an apparent convergence toward the Sun in the same way parallel railroad tracks seem to converge in the distance.
This image of some bright crepusculars was made late one afternoon in Bedford, NY. Note the particularly dark shadow on the right side of the photo, also parallel to the light rays, cast by the clouds there.

Upcoming Leonid Meteor Shower 11/17-18/2009

noreply@blogger.com (Steve Kluge) — Tue, 10 Nov 2009 10:00:00 +0000

(image courtesy of http://leonid.arc.nasa.gov/HDTV_LEO50mm-1.jpg)

This year's Leonids should put on a good show, as the New Moon will not be in the nighttime sky. Peak viewing will be in the wee hours of the night of November 17-18. Here's some good information on how to view meteor showers, and information on all the periodic meteor showers we experience throughout the year.
See the Westchester Astronomers November newsletter for more upcoming sky related events.

Boring Clams are Interesting!

noreply@blogger.com (Steve Kluge) — Thu, 05 Nov 2009 10:36:00 +0000

While attending the Earth Science Information Partners conference at UC Santa Barbara last summer, I enjoyed a nice walk along the beach from the dorms to the conference center each morning. I was struck particularly by the vast number of holes apparently drilled into the rocks along the shore, many of them containing clam shells that just fit into the holes. A closer look at those shells reveals that it's the clams themselves that make those holes!
Examination of the clam shells reveals the sharp ridges visible in the close-up picture on the right. By persistent grinding and rotation of the cutting edges of their shells against the rock, these "rock boring clams" create safe homes for themselves in solid rock, and in doing so accomplish significant weathering of the shoreline rocks, and contribute significant sand to the beach. You can read more about boring clams here:
http://tinyurl.com/boringclams

The "tilted" crescent Moon

noreply@blogger.com (Steve Kluge) — Sun, 01 Feb 2009 13:22:00 +0000

Last week, a friend noticed that the new crescent Moon seemed to be illuminated more nearly on the bottom of the disk of the moon, rather than on the side, and wondered if there was some relationship between that observation and the solar eclipse a few days before.
It turns out that there's no relationship to the eclipse, but rather to the time of the year.
Pretty much, the horns of the crescent coincide with the north and south poles of the Moon, so the waxing crescent pretty much illuminates the "right" side of the Moon (what we call the western limb when viewed from earth), and is centered pretty much on the orbital path of the Moon, and the Moon's equator (not quite, because the Moon's orbit is not quite on the ecliptic). But the illuminated portion of the waxing crescent will appear to be nearer the "bottom" of the Moon as it sets, near the right side of the Moon as it crosses your meridian, and near the "top" of the rising Moon. See the screen shots from http://stellarium.org below:

The Waxing Crescent Moon setting on 1/29/09 (note that the ecliptic is making a fairly steep angle with the western horizon, and that the Moon is north of the ecliptic. The north pole of the Moon is on the "right" side of the moon here, and the Moon's equator is almost vertical:

This was the Moon at meridian crossing on 1/29/09. View is to the south, of course. You could have seen it naked eye if you looked in the right place (you can see Venus naked eye, too!) Notice that the illuminated crescent is pretty much on the right (western limb) side.

Here's the Moon rising on the morning 1/29/09. Notice that the illuminated portion of the Moon is kind of "on top", but that the angle the ecliptic makes with the horizon is less steep than the angle it makes at sunset, so the crescent is not quite as "on top" as it was "on the bottom" when it set.

The places where the celestial equator (blue) and the ecliptic (red) cross are the equinoxes, and the equinox in these images is the vernal (spring) equinox. When the vernal equinox is setting, the angle between the ecliptic and the western horizon is large (the ecliptic is more nearly vertical). When the sun is near the vernal equinox (March and April), the angle between the ecliptic and the horizon at sunset is at its greatest, and Venus and Mercury, if they're east of the Sun (and therefore setting after it), will be high in the sky right after sunset.

Similarly, in September and October as the autumnal equinox rises, the angle between the ecliptic and the eastern horizon at sunrise is the greatest, and around the autumnal equinox Venus and Mercury, if they're west of the Sun (and therefore rising before it), will be high in the sky and well placed for viewing.

The following screen shots show, in order, the rising vernal equinox, the setting vernal equinox, the rising autumnal equinox, and the setting autumnal equinox.

Rising Vernal Equinox (low angle ecliptic)

Setting Vernal Equinox (high angle ecliptic)

Rising Autumnal Equinox (high angle ecliptic)

Setting Autumnal Equinox (low angle ecliptic)

You should also note that the celestial equator makes an angle with the horizon of (90-latitude) (I have Stellarium set to White Plains, NY at 41N), and it remains constant throughout the year.

If you've never imagined it, think of the ecliptic wobbling across the sky each day. And if you can't imagine it, run Stellarium at high speed, and watch it.

Now, back to my friend's question! Eclipses occur as the Moon crosses the ecliptic on its way north or south (called the "nodes" of the Moon's orbit). That's why solar and lunar eclipses come in pairs about 2 weeks apart (a lunar at one node, and a solar at the other), and the eclipse pairs occur every six months or so when the nodes line up with the Sun! The nodes drift with respect to the sun, but in recent years the eclipses have been occurring in the winter and summer. Winter waxing crescents, for the reasons described above, tend to look like they're lit on the "bottom" But watch the crescent moon after the July 22, 2009 solar eclipse....it'll look like this:

A Gibbous Venus...

noreply@blogger.com (Steve Kluge) — Tue, 09 Dec 2008 01:05:00 +0000

If you take a look at my post of 12/1, both planets look pretty round. But realizing that Venus goes through a cycle of phases, I wondered if the camera picked up that level of detail. I went back to the original hi res image, and enlarged Venus to get the image posted here. Sure enough, the gibbous phase of Venus is clearly visible in the photo! I'd seen pictures before, but had never observed the phases myself.
Notice that in the 12/1 photo Jupiter, many times larger than Venus and more than 40 times the diameter of the Moon, appears as a small, round dot of light almost 6 times farther from Earth than the Sun - and the nearby Moon was just "passing through" on it's monthly revolution around Earth.

Amazing Lenticular Clouds over Mt, Rainier

noreply@blogger.com (Steve Kluge) — Sat, 06 Dec 2008 13:05:00 +0000

Folks around Mt. Rainier in Washington state were treated to a spectacular display of "lenticular clouds", formed as a wave of moist air moved over the peak on 12/5/2008. Komonews ran a short article which included some fantastic pictures.

You can find a brief explanation of lenticular clouds here on Wikipedia.

Some years ago, I photographed a lenticular over the Adirondack Mts. that was later featured as an Earth Science Picture of the Day.

Sometimes a similar process produces clouds as stable air moves over a rising column of air. I stopped along the Taconic Parkway one summer evening to photograph this example.

Moon, Venus, and Jupiter Conjunction

noreply@blogger.com (Steve Kluge) — Tue, 02 Dec 2008 01:53:00 +0000

Last night was a washout...gray, wet, and dreary. Today, the skies cleared and I got this shot at Lasdon Park in Somers this evening. See more pics on my Flickr page. Conjunctions like this are not unusual or rare, but they are quite noticeable and dramatic in the evening sky. (A lunar eclipse like this one in February earlier this year provided another not so unusual but interesting show)

Nice View of the Moon, Venus, and Jupiter This Weekend

noreply@blogger.com (Steve Kluge) — Sat, 29 Nov 2008 01:17:00 +0000

Sunday night (November 30), right after sunset, take a few minutes to view the new crescent Moon approaching Venus and Jupiter in the southwestern sky.
Use your fist held at arm's length to measure the angular distance from the Moon up to Venus (the brighter and lower of the 2 planets)- your fist at arm's length is 10 degrees wide. Here's a Stellarium view of what you'll see - the red line is the plane of the ecliptic.

On the evening of 12/1 (Monday night), the Moon will have moved eastward to a position just to the east of Venus. Using your fist again, estimate how far past Venus the Moon is, and add that measurement to last night's to estimate how far eastward among the stars the Moon has moved in the last 24 hours.

Divide that number into 360 degrees to calculate the approximate number of days it takes the Moon to go through a cycle of phases (called the synodic period*) I'll post my results here next week.

*Here's a diagram that explains the sidereal (one revolution) and synodic (one cycle of the phases) of the Moon. If you measured the Moon's eastward progress against the stars, you could calculate the sidereal period. But since Venus is moving eastward against the stars, too (with the Sun), you're really measuring the synodic period.

Now take a look at this LA Times article, and pay close attention to the image. Can you tell what's wrong? Can you explain how it might have happened?