Starship Asterisk*

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.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

Hmm... somew-h-e-r-e under the rainb-o-w, way down low...

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.

:---[===] *

Beautiful phenomenon and picture!

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!

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

How can their be double rainbows if this is true?

"there", not "their" .

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 )

Of course it's astronomy; it's on APOD!

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.

Thanks Chris.

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?

Margarita

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.

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.

Margarita

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

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

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.

Only in Paris!

bystander wrote: C'est un arc en ciel.

nonono, this is a picture of a rainbow

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

So

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.

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).

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.