APOD: A Horizon Rainbow in Paris (2013 Mar 27)

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APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby APOD Robot » Wed Mar 27, 2013 4:06 am

Image A Horizon Rainbow in Paris

Explanation: Why is this horizon so colorful? Because, opposite the Sun, it is raining. What is pictured above is actually just a common rainbow. It's uncommon appearance is caused by the Sun being unusually high in the sky during the rainbow's creation. Since every rainbow's center must be exactly opposite the Sun, a high Sun reflecting off of a distant rain will produce a low rainbow where only the very top is visible -- because the rest of the rainbow is below the horizon. Furthermore, no two observers can see exactly the same rainbow -- every person finds themselves exactly between the Sun and rainbow's center, and every observer sees the colorful circular band precisely 42 degrees from rainbow's center. The above image featuring the Eiffel Tower was taken in Paris, France last week. Although the intermittent thunderstorms lasted for much of the day, the horizon rainbow lasted for only a few minutes.

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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby Beyond » Wed Mar 27, 2013 4:13 am

Hmm... somew-h-e-r-e under the rainb-o-w, way down low...
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby Boomer12k » Wed Mar 27, 2013 5:54 am

Interesting phenomena....never seen one like that...

Here is a good example, and explanation...
http://www.atoptics.co.uk/rainbows/primalt.htm

So it is a FULL rainbow but only the tip is visible at the horizon, as in the example.

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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby fausto.lubatti » Wed Mar 27, 2013 9:07 am

Beautiful phenomenon and picture!
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby RedFishBlueFish » Wed Mar 27, 2013 9:52 am

Cette photo a été prise du RER, n'est-ce pas?

If so, someone is very fast with their camera.

Remarkable.

Oh, and thanks to APOD for not listening to those chawbacons who complain whenever the Amazing Picture Of the Day is of terrestrial phenomenon and that you continue to show intriguing non-telescopic images such as this!
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby kgolemm@gmail.com » Wed Mar 27, 2013 1:44 pm

"every observer sees the colorful circular band precisely 42 degrees from rainbow's center"

How can their be double rainbows if this is true?
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby kgolemm@gmail.com » Wed Mar 27, 2013 1:46 pm

"there", not "their" :ssmile: .
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby gmPhil » Wed Mar 27, 2013 2:06 pm

Very pretty and interesting and all, but... not really astronomy, is it? If the fact that it's partly down to light from the sun, I could post a picture of my cat and call that astronomy too. (Well, if I had a cat, that is... maybe I'd do better to post a picture of a laden dinner table and call it gastronomy :ssmile: )
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby owlice » Wed Mar 27, 2013 2:11 pm

Of course it's astronomy; it's on APOD!
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby Chris Peterson » Wed Mar 27, 2013 2:16 pm

kgolemm@gmail.com wrote:"every observer sees the colorful circular band precisely 42 degrees from rainbow's center"

How can their be double rainbows if this is true?

Because the reference here is to the primary rainbow, with its 42° radius. A double rainbow also shows a secondary band at 51°. It's not visible here because 9° above the horizon is above the rain, and at the edges, where it might be present, it's lost against the buildings of the city.
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby kgolemm@gmail.com » Wed Mar 27, 2013 2:21 pm

Thanks Chris.
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby MargaritaMc » Wed Mar 27, 2013 2:43 pm

owlice wrote:Of course it's astronomy; it's on APOD!


A thought - do (or could) any other planets/moons/asteroids of the solar system have any kind of equivalent to a 'rain'bow?

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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby Chris Peterson » Wed Mar 27, 2013 3:03 pm

MargaritaMc wrote:A thought - do (or could) any other planets/moons/asteroids of the solar system have any kind of equivalent to a 'rain'bow?

Any body with an atmosphere capable of suspending droplets of liquid could have rainbows. Besides Earth, that includes both Venus and Titan. Both have dense enough atmospheres that direct rays of sunlight rarely if ever reach the ground, but we might expect rainbows to be visible from higher up. It's possible that there may be liquid phases high enough in the atmospheres of the gas giants for rainbows to be present, as well. Probably in none of these cases would the causative liquid be water, so both the index of refraction and dispersion would be different, meaning these rainbows would be at radii different from 42°, and would appear narrower or broader than the rainbows we are familiar with.

Rainbow-like phenomena such as nacreous clouds and various halos might possibly be present on Mars, which is capable of sustaining clouds occasionally.
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby MargaritaMc » Wed Mar 27, 2013 3:51 pm

Chris Peterson wrote:
MargaritaMc wrote:A thought - do (or could) any other planets/moons/asteroids of the solar system have any kind of equivalent to a 'rain'bow?

Any body with an atmosphere capable of suspending droplets of liquid could have rainbows. Besides Earth, that includes both Venus and Titan. Both have dense enough atmospheres that direct rays of sunlight rarely if ever reach the ground, but we might expect rainbows to be visible from higher up. It's possible that there may be liquid phases high enough in the atmospheres of the gas giants for rainbows to be present, as well. Probably in none of these cases would the causative liquid be water, so both the index of refraction and dispersion would be different, meaning these rainbows would be at radii different from 42°, and would appear narrower or broader than the rainbows we are familiar with.

Rainbow-like phenomena such as nacreous clouds and various halos might possibly be present on Mars, which is capable of sustaining clouds occasionally.


Thanks, Chris. I had been wondering about Titan, but hadn't realised that the atmosphere of Mars sustained clouds occasionally.
And this really underlies the importance of this kind of 'terrestrial' Apod, I feel. It gets us (well, me) thinking about the phenomena that we observe on this planet and seeing what can be extrapolated from it about other planets.

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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby guessed » Wed Mar 27, 2013 5:30 pm

APOD Robot wrote:Furthermore, no two observers can see exactly the same rainbow


Ceci n'est pas un arc en ciel. - Magritte
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby bystander » Wed Mar 27, 2013 5:55 pm

guessed wrote:
APOD Robot wrote:Furthermore, no two observers can see exactly the same rainbow


Ceci n'est pas un arc en ciel. - Magritte

C'est un arc en ciel.
Boomer12k wrote:Interesting phenomena....never seen one like that...

Here is a good example, and explanation...
http://www.atoptics.co.uk/rainbows/primalt.htm

So it is a FULL rainbow but only the tip is visible at the horizon, as in the example.
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby Psnarf » Wed Mar 27, 2013 7:40 pm

Only in Paris!
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby guessed » Thu Mar 28, 2013 2:37 pm

bystander wrote:C'est un arc en ciel.


nonono, this is a picture of a rainbow :lol2:
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby MargaritaMc » Fri Mar 29, 2013 11:56 pm

"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby Beyond » Sat Mar 30, 2013 1:20 am

So :?:
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby MargaritaMc » Sat Mar 30, 2013 5:49 am

MargaritaMc wrote:http://apod.nasa.gov/apod/ap110401.html
"It's raining on Titan"

Because
Chris Peterson wrote:
MargaritaMc wrote:A thought - do (or could) any other planets/moons/asteroids of the solar system have any kind of equivalent to a 'rain'bow?

Any body with an atmosphere capable of suspending droplets of liquid could have rainbows. Besides Earth, that includes both Venus and Titan. Both have dense enough atmospheres that direct rays of sunlight rarely if ever reach the ground, but we might expect rainbows to be visible from higher up. It's possible that there may be liquid phases high enough in the atmospheres of the gas giants for rainbows to be present, as well. Probably in none of these cases would the causative liquid be water, so both the index of refraction and dispersion would be different, meaning these rainbows would be at radii different from 42°, and would appear narrower or broader than the rainbows we are familiar with.

Rainbow-like phenomena such as nacreous clouds and various halos might possibly be present on Mars, which is capable of sustaining clouds occasionally.
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
— Dr Debra M. Elmegreen, Fellow of the AAAS
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby Gilles » Tue Apr 30, 2013 12:59 am

It should be noted that the explanation in the caption contradicts the one given in the source, an article on MailOnline. APOD states that the display is simply a rainbow, seen very low on the horizon. The newspaper calls it a "horizontal rainbow" or "fire rainbow", which (as correctly stated in their text) is actually not a rain bow, but a ice halo, called the circumhorizon arc. Both atmospheric phenomena require the Sun to be high in the sky. But it cannot be high enough, at the latitude of Paris, at that time of the year, to produce a circumhorizon arc. So it must be a mere rainbow (one can indeed see the downward curvature of the bow, and of course the stormy clouds suggest the presence of rain).
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Re: APOD: A Horizon Rainbow in Paris (2013 Mar 27)

Postby owlice » Tue Apr 30, 2013 2:57 am

Right -- the MailOnline article is incorrect in calling it a "fire rainbow." The term "fire rainbow" is nonsensical, made up by a journalist somewhere. Referring to this rainbow's appearance as horizontal even though it is a regular rainbow strikes me as quite okay.

Though the article was linked to from the text, it was NOT the source for the image, which was submitted to APOD by the photographer.
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