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APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 5:06 am
by APOD Robot
Anticrepuscular Rays Over Colorado
Explanation: What's happening over the horizon? Although the scene may appear somehow
supernatural, nothing more unusual is occurring than a
setting Sun and some well placed clouds. Pictured above are
anticrepuscular rays. To understand them, start by picturing common
crepuscular rays that are seen any time that
sunlight pours though scattered clouds. Now although sunlight indeed travels along
straight lines, the projections of these lines onto the
spherical sky are
great circles. Therefore, the
crepuscular rays from a
setting (or rising) sun will appear to re-converge on the other side of the sky. At the anti-solar point 180 degrees around from the
Sun, they are referred to as
anticrepuscular rays. Pictured above is a particularly striking set of
anticrepuscular rays photographed in 2001 from a moving car just outside of Boulder,
Colorado,
USA.
[/b]
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 6:12 am
by anonymoose
I know it is an extended holiday weekend, but with all of the amazing shots that people post here to be considered for the APOD, do we need a repeat of an APOD pic
from two years ago?. With the exact same description to boot.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 6:32 am
by starman0955
And you make the same mistake again.
There is no such word as "anticrepuscular"!!!!!!!!!!!!!!!!!!!!!
The word crepuscular means "twilight".
So to talk of anti-twilight is stupid.
These rays are crepuscular whether they are seen in the east or west. They are still crepuscular.
Please publish a correction so that the world can get the message.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 6:44 am
by owlice
Anticrepuscular rays:
http://en.wikipedia.org/wiki/Anticrepuscular_rays
Stunning image, and yes, APODs get repeated by design. It has always been so, and is done for various reasons; please see question 4 here:
http://antwrp.gsfc.nasa.gov/apod/ap_faq.html
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 7:03 am
by Chris Peterson
starman0955 wrote:And you make the same mistake again.
There is no such word as "anticrepuscular"!!!!!!!!!!!!!!!!!!!!!
The word crepuscular means "twilight".
So to talk of anti-twilight is stupid.
These rays are crepuscular whether they are seen in the east or west. They are still crepuscular.
Please publish a correction so that the world can get the message.
There is such a word, for the very reason that people have coined it and use it. Whether the derivation is logical or not doesn't really matter. If that were a criterion for valid words, English would suddenly lose a good bit of its vocabulary.
These are indeed crepuscular rays. But they are also anticrepuscular rays, which define a specific class of crepuscular rays that are on the opposite side of the sky from the light source that produces them.
The term is clearly here to stay; get used to it.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 11:48 am
by Les Cowley
>starman0955 wrote:And you make the same mistake again.
>There is no such word as "anticrepuscular"..
Anticrepuscular and crepuscular are accepted meteorological terms. See the American Meteorological Society 'Glossary of Meteorology'
anticrepuscular -
http://amsglossary.allenpress.com/gloss ... e?s=a&p=61
crepuscular -
http://amsglossary.allenpress.com/gloss ... ular-rays1
Team members of the Glossary -
http://amsglossary.allenpress.com/glossary/preface2 - are experts in particular areas and go to considerable care and labor in compilation.
Les Cowley
Atmospheric Optics -
http://www.atoptics.co.uk
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 12:07 pm
by zbvhs
Relative to the Sun, the light rays are essentially parallel. Perspective makes them appear to converge in the East. (I assume the view is to the East.) As for old stuff: it's a holiday season. Let the APOD guys have a break. Sheesh.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 12:25 pm
by neufer
zbvhs wrote:
Relative to the Sun, the light rays are essentially parallel.
Perspective makes them appear to converge in the East. (I assume the view is to the East.)
Yes, it is curious that the APOD is suggesting that these anticrepuscular rays are the result
of scattered clouds when they are clearly the product of the Rockies to the West.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 12:34 pm
by orin stepanek
Whether you like today's APOD or not; It is a neat picture. Anyway I like it.
![Smile :)](./images/smilies/icon_smile.gif)
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 2:46 pm
by Chris Peterson
neufer wrote:Yes, it is curious that the APOD is suggesting that these anticrepuscular rays are the result
of scattered clouds when they are clearly the product of the Rockies to the West.
I disagree. You don't normally see crepuscular rays here in Colorado. The only time I have ever seen them is when there are clouds near the horizon. If the shadows were cast by mountains, sights like this would be daily occurrences.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 3:16 pm
by G00k
I remembered this APOD as well. To check myself, I searched "Anticrepuscular Rays Over Colorado " to find that it is a recurring treat for APOD aficianados. It has, however, a very eccentric orbit, having been seen three times actually since being captured by APOD's gravitational well - on 31 October 2001, and 16 November 2008.
The long delay between the first and second sighting might have been caused by disturbances in the Force caused by the election of Gov. Schwarzenegger (7 October 2003), the reelection of GWB (2 November 2004) and the release of Windows Vista (8 November 2006).
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 3:22 pm
by LF
One of my favorite Earth APOD offerings. Thanks!
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 3:23 pm
by neufer
Chris Peterson wrote:neufer wrote:
Yes, it is curious that the APOD is suggesting that these anticrepuscular rays are the result
of scattered clouds when they are clearly the product of the Rockies to the West.
I disagree. You don't normally see crepuscular rays here in Colorado.
The only time I have ever seen them is when there are clouds near the horizon.
If the shadows were cast by mountains, sights like this would be daily occurrences.
But Guffey is a full kilometer higher than Boulder (so the mountains are less imposing).
http://en.wikipedia.org/wiki/Guffey,_Colorado wrote:
<<Guffey, Colorado, population 26, is semi-famous for electing animals Mayor of Guffey, although such an office does not officially exist. The last known Mayor of Guffey is a cat named Monster (elected in 1998). According to local folklore, the two main political parties in Guffey are called the "Democats" and the "Repuplicans". The town is perhaps less famous for the annual Fourth of July Chicken Fly, during which chickens are ejected from a mailbox atop a ten-foot-high platform; prizes are awarded for distance.>>
I'll bet that Ann is a Democat.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 3:30 pm
by drollere
very nice. but the geometry here actually comes straight out of the renaissance: parallel rays appear to converge to a point, known as the vanishing point. this is a classic central perspective projection.
there is an intriguing and turbulent (fluid and chaotically mixed) boundary between art and science. bending the explanations a little toward art at times is not, scientifically speaking, a bad thing. this is another way of saying that knowledge is a combination of proof, and of esthetics.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 3:52 pm
by Chris Peterson
neufer wrote:But Guffey is a full kilometer higher than Boulder (so the mountains are less imposing).
I'm not sure how much that really matters, as the general shape of the mountains on the horizon is basically the same from either place. But I wasn't actually commenting on seeing crepuscular rays from Guffey, but from seeing them along the Front Range- the long strip just east of the mountains that includes Denver, Colorado Springs, and Boulder. I've been along there enough times to know that anticrepuscular rays only show up when there are clouds over the mountains.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 4:15 pm
by biddie67
Hi - i'm a little confused. The description mentions a SETTING sun. If the picture is taken towards the WEST, wouldn't the light rays be called crepuscular? I would think that they could only be labelled anticrepuscular is the photo was taken facing eastward during a setting sun.
With the sky so full of light, it seems that the photo was taken facing westward; the sky would be darker if it were taken towards the east.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 4:47 pm
by neufer
biddie67 wrote:Hi - i'm a little confused. The description mentions a SETTING sun. If the picture is taken towards the WEST, wouldn't the light rays be called crepuscular? I would think that they could only be labelled anticrepuscular is the photo was taken facing eastward during a setting sun.
With the sky so full of light, it seems that the photo was taken facing westward; the sky would be darker if it were taken towards the east.
Well, it's not that close to setting and perhaps Chris is right that it is caused by high clouds over the Rockies.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 5:04 pm
by owlice
biddie, yes, if the picture had been taken facing west, these would be crepuscular rays. Seems not to be the case, though, given the labeling.
Here's another example of bright anticrepuscular rays:
http://www.flickr.com/photos/fortphoto/3314360660/
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 5:18 pm
by Chris Peterson
biddie67 wrote:Hi - i'm a little confused. The description mentions a SETTING sun. If the picture is taken towards the WEST, wouldn't the light rays be called crepuscular? I would think that they could only be labelled anticrepuscular is the photo was taken facing eastward during a setting sun.
With the sky so full of light, it seems that the photo was taken facing westward; the sky would be darker if it were taken towards the east.
The picture was taken towards the east; looking west from Boulder, or anywhere near it, you see the mountains.
It is impossible to tell in a picture just how bright the sky actually was. But usually, crepuscular rays show up when the Sun is still above the horizon, so the sky is typically quite bright.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Sun Nov 28, 2010 6:50 pm
by León
No good explanation of Apod (above) says otherwise, I say this as I understand it, at dusk the light travels along the surface portion where the observer and partly by the other side, which mirrors a system of clouds ordinates are occasional light reentering the horizon opposite the start.
Rays on the opposite side to the sun also enter from below and not from above as it should according to the explanation
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Mon Nov 29, 2010 3:24 pm
by montylc2001
From my vantage point in Fort Worth, Texas, these rays can be seen daily during sunset in the early summer (not the same rays of course) for about a 3 week period. However, seeing as the pattern is the same every day I came to the conclusion long ago that clouds were not the cause, rather the sunlight shining between mountain peaks. One day I will do the research to determine which mountains.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Mon Nov 29, 2010 4:29 pm
by neufer
montylc2001 wrote:
From my vantage point in Fort Worth, Texas, these rays can be seen daily during sunset in the early summer (not the same rays of course) for about a 3 week period. However, seeing as the pattern is the same every day I came to the conclusion long ago that clouds were not the cause, rather the sunlight shining between mountain peaks. One day I will do the research to determine which mountains.
One thing I always enjoyed about Fort Worth, Texas, was all those mountain vistas.
http://en.wikipedia.org/wiki/North_American_Monsoon wrote:
<<The North American monsoon, variously known as the Southwest United States monsoon, the Mexican monsoon, or the Arizona monsoon, is experienced as a pronounced increase in rainfall from an extremely dry June to a rainy July over large areas of the southwestern United States and northwestern Mexico. These summer rains typically last until mid-September when a drier regime is reestablished over the region. Geographically, the NA monsoon precipitation region is centered over the Sierra Madre Occidental in the Mexican states of Sinaloa, Durango, Sonora and Chihuahua.
The North American Monsoon is not as strong or persistent as its Indian counterpart, mainly because the Mexican Plateau is not as high or as large as the Tibetan Plateau in Asia. However, the North American Monsoon shares most of the basic characteristics of its Indian counterpart. There is a shift in wind patterns in summer which occurs as Mexico and the southwest U.S. warm under intense solar heating. As this happens, the flow reverses. The prevailing winds start to flow from moist ocean areas into dry land areas.
The North American monsoon is associated with an area of high pressure called the subtropical ridge that moves northward during the summer months and a thermal low (a trough of low pressure which develops from intense surface heating) over the Mexican Plateau and the Desert Southwest of the United States. The monsoon begins in late May to early June in southern Mexico and quickly spreads along the western slopes of the Sierra Madre Occidental, reaching Arizona and New Mexico in early July. The monsoon extends into the southwest United States as it matures in mid July when an area of high pressure, called the monsoon or subtropical ridge, develops in the upper atmosphere over the Four Corners region, creating an easterly to southeasterly wind flow aloft.
Pulses of low level moisture are transported primarily from the Gulf of California and eastern Pacific. The Gulf of California, a narrow body of water surrounded by mountains, is particularly important for low-level moisture transport into Arizona and Sonora. Upper level moisture is also transported into the region, mainly from the Gulf of Mexico by easterly winds aloft. Once the forests of the Sierra Madre Occidental green up from the initial monsoon rains, evaporation and plant transpiration can add additional moisture to the atmosphere which will then flow into Arizona. Finally, if the southern Plains of the U.S. are unusually wet and green during the early summer months, that area can also serve as a moisture source.
Monsoons play a vital role in managing wildfire threat by providing moisture at higher elevations and feeding desert streams. Heavy monsoon rain can lead to excess winter plant growth, in turn a summer wildfire risk. A lack of monsoon rain can hamper summer seeding, reducing excess winter plant growth but worsening drought.
Flash flooding is a serious danger during the monsoon season. Dry washes can become raging rivers in an instant, even when no storms are visible as a storm can cause a flash flood tens of miles away (never camp in a dry wash in the desert). Lightning strikes are also a significant danger. Because it is dangerous to be caught in the open when these storms suddenly appear, many golf courses in Arizona have thunderstorm warning systems.
Rainfall during the monsoon is not continuous. It varies considerably, depending on a variety of factors. There are usually distinct "burst" periods of heavy rain during the monsoon, and "break" periods with little or no rain. Monsoon precipitation, however, accounts for a substantial portion of annual precipitation in northwest Mexico and the Southwest U.S. Most of these areas receive over half their annual precipitation from the monsoon.
The North American Monsoon circulation pattern typically develops in late May or early June over southwest Mexico. By mid to late summer, thunderstorms increase over the "core" region of the southwest U.S. and northwest Mexico, including the U.S. and Mexican states of Arizona, New Mexico, Sonora, Chihuahua, Sinaloa and Durango. The monsoon typically arrives in mid to late June over northwest Mexico, and early July over the southwest U.S. Once the monsoon is underway, mountain ranges, including the Sierra Madre Occidental and the Mogollon Rim provide a focusing mechanism for the daily development of thunderstorms. Thus much of the monsoon rainfall occurs in mountainous terrain. For example, monsoon rainfall in the Sierra Madre Occidental typically ranges from 10 to 15 inches. Since the southwest U.S. is at the northern fringe of the monsoon, precipitation is less and tends to be more variable. Areas further west of the core monsoon region, namely California and Baja California, typically receive only spotty monsoon-related rainfall. In those areas, the intense solar heating isn't strong enough to overcome a continual supply of cold water from the North Pacific Ocean moving down the west coast of North America. Winds do turn toward the land in these areas, but the cool moist air actually stabilizes the atmosphere. The monsoon pushes as far west as the Peninsular Ranges and Transverse Ranges of southern California, but rarely reaches the coastal strip. As shown in the panorama above, a wall of thunderstorms, only a half-hour's drive away, is a common sight from the sunny skies along the coast during the monsoon.
This monsoon ridge is almost as strong as the one which develops over Asia during the summer. However, since the lower level moisture flow is not as persistent as in the Indian monsoon, the upper level steering pattern and disturbances around the ridge are critical for influencing where thunderstorms develop on any given day. The exact strength and position of the subtropical ridge also governs how far north the tropical easterly winds aloft can spread. If the ridge is too close to a particular area, the sinking air at its center suppresses thunderstorms and can result in a significant monsoon "break." If the ridge is too far away or too weak, the east winds around the high are inadequate to bring tropical moisture into the mountains of Mexico and southwest U.S. However, if the ridge sets up in a few key locations, widespread and potentially severe thunderstorms can develop.
Unlike the Pacific region of the United States and the west coast of Baja California, precipitation in the NA monsoon is not associated with large-scale mid-latitude cyclones, but with thunderstorms which have very different spatial/temporal distribution characteristics. The difficulty in understanding the variability of summertime convective activity in the southwestern U.S. and northwestern Mexico results from the complex interactions between atmospheric circulation features at both the synoptic (100 to 1000 km spatially, 1 day to 1 week, temporally) and mesoscale (several km to 100 km, hours to one day temporally) and the extremely varied topography. The larger-scale atmospheric motions may control the distribution of water vapor and the general stability or instability (that is, the tendency to form storms) in the atmosphere; nevertheless, local topographic effects are critical to the geographic and even temporal distribution of convective activity.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Mon Nov 29, 2010 10:53 pm
by montylc2001
You misconstrue. The rays I write of are after sunset and made by a range of mountains just past the horizon, which has to be part of the rockies.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Mon Nov 29, 2010 11:03 pm
by neufer
montylc2001 wrote:
You misconstrue.
The rays I write of are after sunset and made by a range of mountains just past the horizon, which has to be part of the rockies.
I construe. The nearest mountains are well into New Mexico.
If Boulder Colorado can't observe anticrepuscular rays off of the Rockies then you sure can't.
Re: APOD: Anticrepuscular Rays Over Colorado (2010 Nov 28)
Posted: Tue Nov 30, 2010 12:24 am
by Chris Peterson
montylc2001 wrote:You misconstrue. The rays I write of are after sunset and made by a range of mountains just past the horizon, which has to be part of the rockies.
The production of crepuscular rays is a basically local phenomenon- shadows from clouds that are typically less than 100 miles away (and usually much closer than that). I don't think there are any candidate mountains within a reasonable distance to the west of Ft Worth that could produce these shadows where you see them.