For Kathy: A Rainbow of Explanations

>> Sunday, April 19, 2009

Kathy said: Yesterday a friend and I were admiring some beautiful clouds on a perfectly sunny and lovely day. We noticed that one very large, oblong cloud was surrounded by not one, but two rainbows. It hadn't rained a drop all day. How is this phenomenon possible without rain?

Such a good question and so many cool things to say and show you. Most people know that rainbows are the refraction of light through water droplets (like rain) in the sky with the water droplet acting like a prism. The full spectrum being seen is a result of seeing light reflected in many water droplets as an individual watching could only see the light refracted at a particular wavelength through a particular droplet. Wikipedia (damn, I love that site) has an excellent write-up of the physics/optics of it as well as some slick pictures.

Here's a key factor: droplets don't have to be falling on you for them to be seen. In fact, if you're standing in the sun and looking on rain in the distance, you stand a much better chance of seeing one. Rainbows can be caused by seaspray (or other water spray), dew, and other mists, basically any water droplets in the atmosphere. Some other cool things about rainbows I gleaned looking into it was that the light below the primary rainbow is lighter than just above it. Look at the picture below and you'll see what I'm talking about.

By Eric Rolph taken at Wrangell-St. Elias National Park, Alaska

You can see the lovely arc of the primary and, above it, the dim vision of the secondary. Notice it's not raining. The Wikipedia link shows rainbows on seaspray and in the spray of a geyser

However, there are other cool types of rainbows even than these like moonbows, rainbows from the light of the moon. How cool is that. Here's a picture.

Photo of a Lunar Rainbow taken from the Zambia side of Victoria Falls. The constellation Orion is visible behind the top of the moonbow. Taken by Calvin Bradshaw.

And there are more cool phenomena, including apparent rainbows in the ice crystals of cirrus clouds like this little lovely. It's called a circumhorizontal arch and there are some cool pictures here, too. And a real stunner taken over Idaho here.
Circumhorizontal arc, photographed in Idaho, June 3, 2006, by Gavin Anderson

So, hope that helped. It's cool stuff.


  • Kathy

    A-ha! Thank you for explaining this to me. We thought how could it be possible for there to be water droplets (or steam or whatever) on such a dry day. But there were clouds, so I suppose that was it!

    My friend also mentioned the moonbow phenomenon that someone told her about. I never heard of that before. Nor had I seen very many "double" rainbows over the years. I remember seeing a double in my neighborhood some years ago after a hard rain. Everyone in the neighborhood came outside. We all stood in the street and marveled at it. What fun!

  • Mike

    Neat photos - I enjoy seeing the rainbow - magic of nature.

  • judemiller1

    How do you embed your pictures in the middle of your blog? I have tried everything people have suggested and when I put the cursor where I want a pix to go in my blog, it always automatically goes to the top of my blog.

    Beautiful pictures by the way.

  • Stephanie B

    judemiller, I thought of you while I was doing this. I followed the advice of a commenter and just added a picture like normal, picking the center position. Then, after it was in my form, I selected it and cut it, went down further in my blog and pasted it.

    No sweat. No html.

  • Quadmama

    Great pictures and I like the new look of the site. I wanted to let you know I gave you an award on my blog today. I'm pretty sure Old West Mom gave you this same award a few months back, so I don't expect you to blog about it, but still wanted you to have it.

  • JD at I Do Things

    Is it wrong that I don't want to know how rainbows work? I just want to enjoy how they look. (And those are some GORGEOUS pictures.)

  • judemiller1

    That's very strange. We have the same program to post our blog and yet I can't do that. I can't even "cut" the picture at the top to paste it further down the post. I have to do a "copy", but then when I place my cursor where I want the pix and hit "paste" it won't...past the pix that is.

    I have tried to get help, but the "help" section isn't very...helpful that is.

    I may have to figure out how to upload a bunch of pix that I want and then try to write my post in between them? I will conquer it yet!!!

  • Phyl

    Those are stunning photos! And that's a great explanation. I thought it would have to have something to do with there still being moisture in the air, even though it's not falling down as rain. (She said, glaring out the window.)

  • Stephanie B

    Kathy, I'm glad I could help.

    Mike, phyl and everyone else that admired the photos, I can't take credit. I didn't take a one of 'em. Even the top photo is from (which is a great resource)

    judemiller, I'm stumped, short of messing with html and I'm not an expert on that.

    Thanks, quadmama. One of the cool things about Ask Me Anything is that this blog does awards and memes. And I appreciate it very much.

    There's nothing wrong with wanting to stick with the magic, JD. Rainbows are lovely. You'll notice I kept the explanation pretty top level. Optics give me a headache. Rainbows don't. 'Nuff said.

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