APOD: Alaskan Moondogs (2013 Jan 26)

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APOD: Alaskan Moondogs (2013 Jan 26)

Post by APOD Robot » Sat Jan 26, 2013 5:06 am

Image Alaskan Moondogs

Explanation: Moonlight illuminates a snowy scene in this night land and skyscape made on January 17 from Lower Miller Creek, Alaska, USA. Overexposed near the mountainous western horizon is the first quarter Moon itself, surrounded by an icy halo and flanked left and right by moondogs. Sometimes called mock moons, a more scientific name for the luminous apparations is paraselenae (plural). Analogous to a sundog or parhelion, a paraselene is produced by moonlight refracted through thin, hexagonal, plate-shaped ice crystals in high cirrus clouds. As determined by the crystal geometry, paraselenae are seen at an angle of 22 degrees or more from the Moon. Compared to the bright lunar disk, paraselenae are faint and easier to spot when the Moon is low.

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epfevv

Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by epfevv » Sat Jan 26, 2013 5:23 am

I don't understand the statement that "...a paraselene is produced by moonlight refracted through thin, hexagonal, plate-shaped ice crystals in high cirrus clouds." As I look at the picture the paraselenae appear to be in front of the mountains which means that they are well below the "high cirrus clouds". They must be produced by the ice crystals from some form of ground moisture or at least lower lying mist or clouds. Can you enlighten me?

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Boomer12k » Sat Jan 26, 2013 9:20 am

Cool looking.

Never seen one, but have seen other halo effects.

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by fausto.lubatti » Sat Jan 26, 2013 9:37 am

Wonderful picture! :D

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Moonlady » Sat Jan 26, 2013 10:10 am

What a beautiful moon picture...if any one disagrees will be turned into werewolf next full moon!!!

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Joe Stieber » Sat Jan 26, 2013 10:11 am

epfevv wrote:I don't understand the statement that "...a paraselene is produced by moonlight refracted through thin, hexagonal, plate-shaped ice crystals in high cirrus clouds." As I look at the picture the paraselenae appear to be in front of the mountains which means that they are well below the "high cirrus clouds". They must be produced by the ice crystals from some form of ground moisture or at least lower lying mist or clouds. Can you enlighten me?
This picture is also featured on Spaceweather.com today: http://spaceweather.com/archive.php?vie ... &year=2013

There it says "The phenomenon is caused by moonlight shining through ice crystals in the air. Hexagonal plate-shaped crystals, fluttering down from the clouds like leaves from trees."

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by saturno2 » Sat Jan 26, 2013 10:17 am

Paraselenae rainbow of Moon at night in Alaska.
Photograph with good contrast

Grumium

Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Grumium » Sat Jan 26, 2013 10:40 am

Can someone tell me what constellations are in the background? I'm usually pretty quick at seeing this, but this time no.
I live on the same latitude as Alaska, so the constellations should be familiar to me, but I don't know what I'm looking at here. So annoying :)

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Joe Stieber » Sat Jan 26, 2013 11:09 am

Grumium wrote:Can someone tell me what constellations are in the background?
The pair of brighter stars on a slightly tilted vertical line above and slightly to the left of the moon are Hamal and Sharatan (Alpha and Beta Arietis). Mesarthim (Gamma Arietis) also dangles down from Sheratan. Above the right-hand moondog, the bright star is Alpheratz (Alpha Andromedae, the northeast corner of the Great Square of Pegasus). To the right of it, near the edge of the frame, is Scheat (Beta Pegasi, the northwest corner of the Great Square).

The diagonal line of fainter stars above the moon, running from the lower left to the upper right, is the eastern rope of Pisces. The western rope runs sort of horizontally into the mountain tops, lost in the glare of the moon. The first star above and slightly to the left of the moon on that line is Eta Piscium, and at the bottom-left of the line (below-left of the distinct cloud to the left of the moon) is Alrisha, Alpha Piscium, the knot in the ropes of Pisces.

The star at the center near the top edge is Alpha Trianguli, and to the right of it (even closer to the top edge) is Mirach, Beta Andromedae.

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by orin stepanek » Sat Jan 26, 2013 12:32 pm

Love this picture 8-)
Moonlady wrote:What a beautiful moon picture...if any one disagrees will be turned into werewolf next full moon!!!
hey Moonlady; how about a real wolf?
Click to play embedded YouTube video.
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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Moonlady » Sat Jan 26, 2013 1:48 pm

orin stepanek wrote:Love this picture 8-)
Moonlady wrote:What a beautiful moon picture...if any one disagrees will be turned into werewolf next full moon!!!
hey Moonlady; how about a real wolf?
Click to play embedded YouTube video.

I love this wolf howling :D reminds me of old times...when I was taking driving lessons for my drivers licence my teacher had his little black dog, in bag size, I dont know the breed,
with us in the car, (he asked me before if I would allow the little dog coming with us) he howled like a wolf! Very loud noise out of that little dog :D :puppy:

Steve Dutch

Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Steve Dutch » Sat Jan 26, 2013 4:05 pm

In mid-latitudes, high cirrus clouds are normally where ice crystals capable of forming halos reside. However, it is possible for ice crystals to form close to the ground, as in the photo here. I have photos of a brilliant sun halo created by windblown snow. It illustrates nicely that optical phenomena in the atmosphere can be at any distance from the observer. If you see a rainbow while it's raining, the rainbow is created by drops anywhere from inches to miles away.

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Ann » Sat Jan 26, 2013 5:40 pm

It's a very beautiful APOD. Thank you, Sebastian Saarloos.

And thank you, Joe Stieber, for identifying the stars for me. I was unable to do so myself, although I wondered about the bright blue star that you identified as Alpheratz, Alpha Andromedae, the top left star in the Great Square of Pegasus. Sheat, Beta Pegasi, the white-looking star that is "touching" the right edge of this picture, is another member of the Great Square of Pegasus. A third member is actually visible, namely Algenib, Gamma Pegasi, the bluish star which can be seen to the left of the rightmost Moon dog, between two clouds.

I'm fascinated at the fact that intrinsically blue stars really do look blue in this picture. Now that Joe Stieber had identified the stars for me I could look them up, and all the blue-looking stars do indeed have negative, "blue", B-V indexes. :D

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by LocalColor » Sat Jan 26, 2013 5:54 pm

Wonderful photo, have only seen a "moondog" once up here (and no camera handy!)

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by bmesser » Sat Jan 26, 2013 6:51 pm

I don't believe this is a true moon dog or halo caused by ice crystals in the higher atmosphere, but as someone else said in an earlier post the phenomena is caused by ice crystals in the lower atmosphere, probably trapped in a temperature inversion in the lowest 300 metres. I think the effect is exactly the same though so what the heck. From what you can see of the sky it looks clear of both cirrus or cirrostratus cloud, and although I know these can be exist as very thin layers at times I don't think the explanation is quite right. There is a weather phenomena called 'diamond dust' that if it was actually happening would I'm sure produce this effect. Diamond dust is barely perceptible as it fall even on skin and can only really be seen if it is lit up by a light source such as a flash light or in this case the moon.

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Joe Stieber » Sat Jan 26, 2013 8:39 pm

Ann wrote:It's a very beautiful APOD. Thank you, Sebastian Saarloos.

And thank you, Joe Stieber, for identifying the stars for me. I was unable to do so myself, although I wondered about the bright blue star that you identified as Alpheratz, Alpha Andromedae, the top left star in the Great Square of Pegasus.
You're welcome Ann!

I suppose you were wondering why a star in Andromeda is the corner of the Great Square of Pegasus? That common corner pre-dates the official IAU boundries circa 1930. You couldn't have a star in two constellations at the same time, so it ended up in Andromeda, but it still marks the corner of the stick figure of the Great Square (which is just an asterism anyway). A simialr situation exists with Alnath, or Beta Tauri, the northen horn tip of Taurus which also marks the southern corner of Auriga's pentagonal stick figure.

And no, I didn't mention every star in the image -- I was just trying to highlight enough of them to get folks oriented. :)

Quigley

Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Quigley » Sat Jan 26, 2013 9:07 pm

I love this wolf howling :D reminds me of old times...when I was taking driving lessons for my drivers licence my teacher had his little black dog, in bag size, I dont know the breed,
with us in the car, (he asked me before if I would allow the little dog coming with us) he howled like a wolf! Very loud noise out of that little dog :D :puppy:[/quote]

Was that little black dog a Schipperke by chance? The breed's name means "little captain" in Flemish since they were used as watch dogs and mousers on the barges years ago. We had neighbors call ours "the wolverine" because of her appearance.

Does fog freeze when the temperatures get cold enough and what kind of ice crystals would that possibly produce?

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by owlice » Sat Jan 26, 2013 9:33 pm

Typically, sun- or moondogs are formed in cirrus clouds; however, in cold climates (or those that emulate them, such as Washington DC's recently), ice crystals can also form in the atmosphere closer to the ground. The Atmospheric Optics site has a nice page on the formation of sun- and moondogs if you are interested in reading more.
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The odd class of "mercury-manganese" linking stars

Post by neufer » Sat Jan 26, 2013 9:38 pm

Joe Stieber wrote:
Ann wrote:
And thank you, Joe Stieber, for identifying the stars for me. I was unable to do so myself, although I wondered about the bright blue star that you identified as Alpheratz, Alpha Andromedae, the top left star in the Great Square of Pegasus.
You're welcome Ann!

I suppose you were wondering why a star in Andromeda is the corner of the Great Square of Pegasus? That common corner pre-dates the official IAU boundries circa 1930. You couldn't have a star in two constellations at the same time, so it ended up in Andromeda, but it still marks the corner of the stick figure of the Great Square (which is just an asterism anyway). A simialr situation exists with Alnath, or Beta Tauri, the northen horn tip of Taurus which also marks the southern corner of Auriga's pentagonal stick figure.
http://stars.astro.illinois.edu/sow/alpheratz.html wrote:
<<ALPHERATZ (Alpha Andromedae). Andromeda runs like a string of pearls to the northeast of the Great Square of Pegasus. Since its three principal stars have almost the same brightness, Beyer simply lettered them Alpha, Beta, and Gamma in order, Alpha and Beta tied for the lead in apparent magnitude. Mid-second magnitude (2.06) Apheratz, the Alpha star, connects Andromeda (the Lady) with Pegasus, the Flying Horse that carried Perseus to Andromeda's rescue. As such, Alpheratz is also the northeastern star of the Great Square of Pegasus. The name has a confused origin possibly transferred from another star, and is commonly taken to mean "the horse's shoulder" or "naval," showing that the star originally belonged more to Pegasus, though now it is formally within the boundaries of Andromeda. As a linking star, Alpheratz is one of two that carries two Greek letter names, and is also Delta Pegasi, though the name is no longer used. (The other star is Elnath, Beta Tauri, which links Taurus to Auriga and is also called Gamma Aurigae.) If you draw a line through Alpheratz and Algenib, Gamma Pegasi to the south, it will pass just to the east of the vernal equinox in Pisces. Alpheratz, at the cool end of the B star range (B8 subgiant) , is still hot, with a temperature of about 13,000 Kelvin. At a distance of 97 light years, we calculate a total luminosity, including the star's ultraviolet radiation, of about 200 times that of the Sun. Alpheratz stands out in a couple of ways. It is a "spectroscopic binary," a close double that can be investigated only through the examination of its spectrum, the pair orbiting each other every 96.7 days. The much dimmer companion seems to be about a tenth the brightness of the principal star. The bright member of the pair, the one that makes the impression on the human eye, is also chemically peculiar, and is the brightest member of the odd class of "mercury-manganese" stars. Compared to our standard, the Sun, and to the vast majority of other stars, the atmosphere of these stars have vast enrichments of these elements, mercury overabundant by a factor of tens of thousands. Other elements such as gallium and europium are hugely enriched as well, while some others are depressed. We believe we are seeing a separation of elements as a result of the inward pull of gravity and the outward pressure of radiation that act differently on different elements.>>
http://stars.astro.illinois.edu/sow/elnath.html wrote:
<<[ELNATH (Alnath, or Beta Tauri)] is one of the sky's rare linking stars. Formally now in Taurus, the star is also a part of the classic outline of Auriga and is simultaneously Gamma Aurigae (though it ranks number two in Auriga as well, after Capella). (The other linking star, Alpheratz or Alpha Andromedae, is also Delta Pegasi.) "Gamma Aurigae" is never used, however.

Elnath is a hot (13,600 Kelvin) class B giant star. From its distance of 130 light years, we find a luminosity (corrected for the ultraviolet radiation from the hot surface) almost 700 times that of the Sun. Like so many stars of its class, Elnath is "chemically peculiar" and appears to be a "mercury-manganese" star, the manganese abundance 25 times normal, the calcium and magnesium abundance reduced and only an eighth solar. These peculiarities are caused by the combined action of gravity and radiation, which make the atoms of some elements drift downward and out of sight and others rise. The best bright example, is, by rather amazing coincidence, the other "linking star," Alpheratz!>>
Art Neuendorffer

epfevv

Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by epfevv » Sat Jan 26, 2013 11:31 pm

Joe Stieber wrote:
epfevv wrote:I don't understand the statement that "...a paraselene is produced by moonlight refracted through thin, hexagonal, plate-shaped ice crystals in high cirrus clouds." As I look at the picture the paraselenae appear to be in front of the mountains which means that they are well below the "high cirrus clouds". They must be produced by the ice crystals from some form of ground moisture or at least lower lying mist or clouds. Can you enlighten me?
This picture is also featured on Spaceweather.com today: http://spaceweather.com/archive.php?vie ... &year=2013

There it says "The phenomenon is caused by moonlight shining through ice crystals in the air. Hexagonal plate-shaped crystals, fluttering down from the clouds like leaves from trees."
That makes sense. Thanks.

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by BDanielMayfield » Sun Jan 27, 2013 1:05 am

Joe Stieber wrote:
Grumium wrote:Can someone tell me what constellations are in the background?
The pair of brighter stars on a slightly tilted vertical line above and slightly to the left of the moon are Hamal and Sharatan (Alpha and Beta Arietis). Mesarthim (Gamma Arietis) also dangles down from Sheratan. Above the right-hand moondog, the bright star is Alpheratz (Alpha Andromedae, the northeast corner of the Great Square of Pegasus). To the right of it, near the edge of the frame, is Scheat (Beta Pegasi, the northwest corner of the Great Square).

The diagonal line of fainter stars above the moon, running from the lower left to the upper right, is the eastern rope of Pisces. The western rope runs sort of horizontally into the mountain tops, lost in the glare of the moon. The first star above and slightly to the left of the moon on that line is Eta Piscium, and at the bottom-left of the line (below-left of the distinct cloud to the left of the moon) is Alrisha, Alpha Piscium, the knot in the ropes of Pisces.

The star at the center near the top edge is Alpha Trianguli, and to the right of it (even closer to the top edge) is Mirach, Beta Andromedae.
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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by DavidLeodis » Sun Jan 27, 2013 10:04 pm

In the explanation to this APOD it mentions "apparations". I wonder if that is the U.S. spelling of "apparitions"?

Interestingly (well hopefully :) ) in the Harry Potter series the word "apparate" is used and in information that I've found it states "To apparate is to transport oneself from one place to another by dissapparating and reapparating, coined from the Latin 'appareo', meaning to appear. Note that while the spelling apparation would seem to be more appropriate for this action, it is almost always spelled apparition in the books".

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by Chris Peterson » Sun Jan 27, 2013 11:18 pm

DavidLeodis wrote:In the explanation to this APOD it mentions "apparations". I wonder if that is the U.S. spelling of "apparitions"?
Nope. It's as much a spelling error in American English as in any other version of English.
Chris

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by DavidLeodis » Mon Jan 28, 2013 12:03 am

Chris Peterson wrote:
DavidLeodis wrote:In the explanation to this APOD it mentions "apparations". I wonder if that is the U.S. spelling of "apparitions"?
Nope. It's as much a spelling error in American English as in any other version of English.
Thanks for your response Chris, which is appreciated. :)

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Re: APOD: Alaskan Moondogs (2013 Jan 26)

Post by neufer » Mon Jan 28, 2013 3:41 am

Chris Peterson wrote:
DavidLeodis wrote:
In the explanation to this APOD it mentions "apparations". I wonder if that is the U.S. spelling of "apparitions"?
Nope. It's as much a spelling error in American English as in any other version of English.
Of course, there was the original
luminous apparition of Pariselene:
  • -------------------------------------------------
    "Pariselene" = Paris & Helene of Troy
    "Brangelina" = Brad Pitt & Angelina Jolie
    "Bennifer" = Ben Affleck & Jennifer Lopez
    "TomKat" = Tom Cruise & Katie Holmes
    -------------------------------------------------
Art Neuendorffer