Though I never seem to be read up on anything.
In the process of writing my off-color, off-topic resistor-code post in another thread, I looked at a number of images with AltaVista’s image search engine, and it seemed that all the natural photos of atmospheric rainbows had red bands at their tops.
I’m too lazy to think optics anymore. Are there combinations of atmospheric conditions and viewing aspects that would ever put a rainbow’s red band at its lower edge?
Ray (Red rises because its hot.)
You would only get red on the bottom of a rainbow if the rainbow was “upside down”, with the middle lower than the ends (I have no idea whether this can happen.)
Shorter wavelengths of light refract more than longer wavelengths in a given media (I can’t remember if this is just a general rule or the case with all refraction, but it works that way here.) Red will always be on the outside of a rainbow and violet will be on the inside.
Rainbows are actually complete circles. We only see an arch because we’re standing on the ground and the rest of the circle is below the horizon. If we were on an aeroplane, then we would see a full ring.
I have no clue if red is always on the outside, the infra-red spectrum would have to be consistent for us to utilise it. Its placement on the spectrum is therefore likely to be permanent.
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I saw a double rainbow once. One rainbow inside another. The orders were reversed in the second rainbow. I don’t remember which rainbow had red on the outside though.
Virtually yours,
J Matrix
How about “glories” or “Brocken’s bows?”
Aren’t they reversed?
You can find several of your answers here:
http://covis.atmos.uiuc.edu/guide/optics/
It’s probably clear by now but the short answer to the OP is that primary rainbows always have red on top and secondary rainbows always have red on the bottom.
The rainbow itself is caused by the reflection of sunlight by raindrops. Because of the spherical shape of the raindrops, the reflected rays are concentrated at a particular angle. The exact value of this angle depends on the index of refraction, which depends, in turn, on the frequency (i.e. color) of the light. The physics governing this process aren’t susceptible to changes because of atmospheric conditions or viewing aspects.
The secondary rainbow (the higher one in a double rainbow) is formed from light that is twice reflected in the raindrop. There are, of course, tertiary and higher rainbows but 1) they are getting pretty dim (not much light is reflected three times or more) and 2) the third and fourth reflections exit out the back of the raindrop, so in order to see them you would have to face the sun. (An ordinary rainbow is only visible when you’re facing away from the sun. The center of the arc is at the antisolar point.)
The area between the primary and secondary bows is known as “Alexander’s Dark Band” (really), named for Alexander of Aphrodisias, an old Greek. It’s dark because that’s where the light that’s being reflected would be if it weren’t reflected.
Inside the primary bow there are sometimes pink and green alternating bands of color, known as supernumerary arcs.
Finally, larger raindrops are better at separating colors and since raindrops tend to get larger as they fall, rainbows tend to be more intense at the bottom (right near the pot o’ gold). Very fine, misting rain tends to create washed out bows. There is even a phenomenon known as a “fog bow”, created by fog droplets, which is almost white.
“Vandelay!! Say Vandelay!!”
pluto, rainbows are caused by refraction of sunlight, not reflection.
Just tryin’ to help.
Those who do not learn from the past are condemned to relive it. Georges Santayana
jab1 – appreciate the help but I’ll try to nail this down a little closer. The formation of the bow is caused by reflection, while the dispersion of the colors is caused by refraction. Fair 'nuff?
“Vandelay!! Say Vandelay!!”
Very fair. I stand corrected. (Or is it “sit”?)
I once saw a rainbow in Florida that was caused by the setting sun. It was much higher in the sky than if it had been caused by the sun earlier in the day. It’s the only time I’ve ever seen a rainbow that was more than half a circle. And the colors were slightly off due to the redness of the sunlight. Impressive.
Those who do not learn from the past are condemned to relive it. Georges Santayana
Once saw a rainbow in a white sand desert after a short cloud burst. the sky behind us was clear the sky behind the rainbow ws dark gray ( BTW you only see a rainbow if the sun is behind you) we could see where the rainbow ends 'touched" the ground just a few hundred yards away. The ‘ends’ were obscured by a shimmering golden light. but no matter how we tried we could not reach the pots of gold, the rainbow kept retreating from us, but if we stayed in place and watched another walk towards it they would be standing in the gold. (Them damn leprchauns was laughing like hell) And we saw this BEFORE we came to the “cactus patch”.well maybe not the leprechaun part. I THINK I have read that if you are at the right altitude, in a plane on a mt top, and the sun is just right you can see a circular rinbow.
“Pardon me while I have a strange interlude.”-Marx
mr john – another way to see a circular rainbow is to stand in a water sprinkler at noon and look down. One of those “spray a fine mist everywhere” kind of sprinklers, not the “back and forth” or the “chukka-chukka” types.
You just need to get your eyes between the sun and a full circle of water droplets. Your other suggestions are good but this one is less trouble (in the summer, anyway!).
“Vandelay!! Say Vandelay!!”