APOD: A Circumhorizontal Arc Over Ohio (2014 May 24)

APOD Robot · Post by **APOD Robot** » Sat May 24, 2014 4:08 am

A Circumhorizontal Arc Over Ohio

Explanation: Why would clouds appear to be different colors? The reason here is that ice crystals in distant cirrus clouds are acting like little floating prisms. Sometimes known as a fire rainbow for its flame-like appearance, a circumhorizon arc lies parallel to the horizon. For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds are present. Furthermore, the numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner. Therefore, circumhorizontal arcs are quite unusual to see. This circumhorizon display was photographed through a polarized lens above Dublin, Ohio in 2009.

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Boomer12k · Post by **Boomer12k** » Sat May 24, 2014 6:46 am

Awesome!!!!! Really Cool!!!!! A FLAT RAINBOW!!!!!

And such a criteria....

:---[===]*

Dr La · Post by **Dr La** » Sat May 24, 2014 9:28 am

Yeah. Only, it isn't a circumzenithal arc. It are iridiscent clouds.

owlice · Post by **owlice** » Sat May 24, 2014 2:47 pm

Dr La wrote:Yeah. Only, it isn't a circumzenithal arc. It are iridiscent clouds.

Right, it's not a circumzenithal arc, and no one said it was. It's a circumhorizontal arc. It is not iridescence, though if clouds are patchy, a circumhorizontal arc can be mistaken for iridescence.

Chris Peterson · Post by **Chris Peterson** » Sat May 24, 2014 3:20 pm

owlice wrote:It's a circumhorizontal arc. It is not iridescence, though if clouds are patchy, a circumhorizontal arc can be mistaken for iridescence.

I'm not sure it's possible from just this image to really say for sure which it is. It would be easier if the FOV were wider. There are elements that make me think it could be iridescence, such as the way that different wavelength bands don't line up with each other. Really hard to say from just the image alone, although I've no reason to doubt the interpretation of the photographer, who had much more context to work from.

owlice · Post by **owlice** » Sat May 24, 2014 3:41 pm

This is a circumhorizontal arc. See here, reference the first appearance of this image.

Chris Peterson · Post by **Chris Peterson** » Sat May 24, 2014 3:57 pm

owlice wrote:This is a circumhorizontal arc. See here, reference the first appearance of this image.

I'm not saying it isn't. But I disagree with Cowley's assessment that it is certainly one. From this image alone, I don't think it's possible to say that with complete confidence. Iridescent clouds can look like that. And this image does show anomalies not expected of a circumhorizontal arc, in particular the vertical fragmentation of color bands. So while there is good evidence that's what this is, I'd avoid stating it as an absolute.

geckzilla · Post by **geckzilla** » Sat May 24, 2014 4:29 pm

The image can be modified to isolate the rainbow to make its colors more apparent as well as the structures which are responsible for the diffraction.

owlice · Post by **owlice** » Sat May 24, 2014 4:50 pm

Look! A rabbit and a horned one-eyed dog!

geckzilla · Post by **geckzilla** » Sat May 24, 2014 6:12 pm

I tried drawing arcs over the spectrum. The breaking up of the color bands seems to mostly be an optical illusion created by the horizontal spaces disrupting the arc.

Chris Peterson · Post by **Chris Peterson** » Sat May 24, 2014 6:15 pm

geckzilla wrote:I tried drawing arcs over the spectrum. The breaking up of the color bands seems to mostly be an optical illusion created by the horizontal spaces disrupting the arc.

Nice.

Boomer12k · Post by **Boomer12k** » Sat May 24, 2014 7:32 pm

Looking up...."Iridescent Clouds"....and seeing a hundred different examples.
And then Looking up "Circumhorizontal Arc", I find them to be similar, but not necessarily the same.

I.C.s can be Water Droplets...not just Ice Crystals....CHAs....would be Ice Crystals....

Circumhorizontal Arcs ALWAYS HAVE.....Red on top....Blue underneath.....they also seem to me...to stretch straight across the sky...where as. I.C.s are a "lit up cloud". CHA's....can be just a small patch of the halo.... The CHA is the LOWER part of a halo....Red in the center of the halo...blue on the outside....thus....the bottom of the halo...Red always on top....

http://www.abovetopsecret.com/forum/thread873605/pg

"Circumhorizon arcs (or CHAs) will always have the same sequence of colours (red on top and blue underneath), and will always be found below the sun in the sky, when it's at a high enough altitude (58° or above) above the horizon. Crucially, the colours will always be in distinct horizontal bands"

A Circumhorizontal Arc is a PART OF A HALO!!! A lower, second, Ice halo...the Sun is always ABOVE IT.....in the Center.

If you Wikipedia the two phenomena...you will see the differences....there is a good example of A Circumhorizontal Arc....and the HALO...where as I.C.s are almost "backlit"....

This IS a Circumhorizontal Arc....I think the Photog got it right.

:---[===] *

LocalColor · Post by **LocalColor** » Sat May 24, 2014 11:29 pm

Whatever it is - it is beautiful! Another example of our amazing world explained by science.

DavidLeodis · Post by **DavidLeodis** » Sun May 25, 2014 10:47 am

It's an interesting and colourful image.

To the top there is what seems to be an aeroplane contrail. Assuming that the plane was not too far away I wonder if passengers on it could have seen the scene and what it would/might have looked like?

Chris Peterson · Post by **Chris Peterson** » Sun May 25, 2014 2:31 pm

DavidLeodis wrote:It's an interesting and colourful image. :)

To the top there is what seems to be an aeroplane contrail. Assuming that the plane was not too far away I wonder if passengers on it could have seen the scene and what it would/might have looked like?

The plane would need to be below the cirrus clouds (unlikely), and positioned so as to maintain the 58° between the cloud and Sun. That wouldn't seem to be the case with the airplane in this image.

DavidLeodis · Post by **DavidLeodis** » Sun May 25, 2014 7:18 pm

Thanks Chris for your help.

aildoux · Post by **aildoux** » Sun May 25, 2014 8:15 pm

Just above the airplane's contrail that can be seen top center is what seems like a star. Could it be daytime Venus?

geckzilla · Post by **geckzilla** » Mon May 26, 2014 2:57 am

aildoux wrote:Just above the airplane's contrail that can be seen top center is what seems like a star. Could it be daytime Venus?

It's a hot pixel. There's another one straight down the same column from it in the lower half of the photo.

Starship Asterisk*

APOD: A Circumhorizontal Arc Over Ohio (2014 May 24)

APOD: A Circumhorizontal Arc Over Ohio (2014 May 24)

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Re: APOD: A Circumhorizontal Arc Over Ohio (2014 May 24)

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