Naked Rainbows

By Phil Plait | November 8, 2005 12:03 am

Warning! This blog entry contains nudity. Sortof. And it’s mine, so really: beware.

A little while back, I did something I rarely do: shower in the afternoon. I’m a morning showerer because it helps wake me up and it relaxes my old stingy muscles.

But this time I broke with tradition, and showered after lunch. It was a warm, cloudless day, so I opened the little window in the shower to let in the sunlight and enjoy the warm afternoon air streaming in. When I looked down, I got a surprise!

No, not shrinkage. When I looked down, I saw… a rainbow. Now, I’m no stranger to apparitions in my shower. But this surprised me. A rainbow, in the shower! How delightful!

The rainbow in question. The rainbow is at the bottom middle of the image. The Sun is well off to the upper left in this image (maybe 130 degrees to the left as I took the shot), and the bright spot is the direct sunlight hitting the shower curtain.

But why did it surprise me? Geometry, that’s why. In general, to see a rainbow, the Sun has to be behind you. That’s because a rainbow is caused when the sunlight is bent twice inside a raindrop. Together, those two bends send the light almost back in the direction it came; actually about 140 degrees. In other words, if your back is to the Sun, the rainbow will be 180 – 140 = 40 degrees in radius, centered on the direction opposite the Sun (this explanation might make more sense).

So to see a rainbow, you have to have your back to the Sun. But in my shower, the geometry was different. I was facing the Sun, more or less. But after some thought (I do some of my best thinking when sprayed with hot water), I realized this all made sense. The window was above my head, and I was looking down. So in a sense the sunlight was coming from behind me. That 40 degree difference from 180 is what made it visible at all, floating above my belly. For the picture I took above, I wound up facing a different direction to get the best angle on the rainbow.

Satisfied, I continued my ablutions. Then something else caught my eye. As I looked straight into the shower stream, I saw lots of droplets flashing colors, especially red:

The colored drops in question. I took this picture facing the stream, with the Sun above me and90 degrees to my left. The lens of the camera fogged up, which is causing the fuzziness and halos.

These colored droplets were well away from the critical 140 degree rainbow angle. I’m still not sure what caused them. I didn’t use a flash for the picture, and I did see the colors with my own eyes.

So I have one solved and one unsolved mystery. But I did learn one important thing: naked science is fun! Almost the most fun thing you can do in a shower.


Comments (20)

  1. Blake Stacey

    “Ablutions” is a funny word.

    In the house where I grew up, the bathrooms were well inside the building, which is good because it meant we had a place to hide during tornado season. When I had an apartment in Cambridge, Mass., the shower had a little window set in the wall, which the sun would strike in early afternoon. If you took a shower from around 13:00 to 15:00, you’d get a rainbow. One more perk of being night-shifted was getting up at noon, eating a breakfast of ice cream and experiencing a shower full of spectra. (And of course, doing physics at midnight just feels so much more hard core.)

  2. You bring a camera when you go showering?

  3. Dee Jay

    Indeed, seems a tad narcissistic… 😉

    Seriously though, neato. Not much I can say about the red drops, so it must be aliens, or ghosts. Alien ghosts. Ever see Final Fantasy Spirits Within? Yeah, those things.

  4. Marlayna

    Hey, not fair. We click on the link expecting to see you nude, and all we get is a rainbow, LOL.

    I think the droplets flashing has something to do with the properties of the surface of the shower curtain. Does it reflect much light? What colour is it? Hmmm, you should take more showers in the afternoon 😀

  5. The two explanations that leap to mind about the red flashes are:

    1) It’s part of a double rainbow. The light is being reflected from lower drops back into higher ones at the proper angle.

    2) You can probably assume that the drops that have fallen as far as your waist are spherical, at least for purposes of back-of-the-envelope calculations. But this may be a very bad assumption for drops that have just left the shower head. The drops that have just broken off from the main jet probably still have some weird shape as momentum, surface tension, gravity, and air resistance interact. Some of these may be bending light in just the right way to send a colored flash into your eye.

    It might be instructive to take a long exposure photo like your second one, to get a statistical sampling of the colors, and see whether they form a pattern.

    (Shower physics: experiment with the one you love.)

  6. Kramer: “OK. Let’s turn the water on now. ”
    Jerry: “No, I told you, it’s just a dry run.”
    Kramer: “Come on, Jerry. How about a-a baggy swimsuit?”
    Jerry: “You’re not gettin’ any skin, Kramer.”
    Kramer: “Well, this has all been one big tease!”

  7. I knew someone would ask about the camera. I’ll just let you folks wonder… and also wonder about the images I didn’t post.

  8. A couple of years ago, I saw a double rainbow for the first time. Oddly enough, I’ve seen them a couple more times since then.

    But I’ve never been able to find any information about what conditions can create that phenomenon. Got any pointers?

  9. TJ

    The explanation of the red drops is simple. You were cogitating on your opening remarks for the blog entry, thought of shrinkage, looked down, flushed with embarrasment, and the red of your skin reflected at an inverse logarithmic pi r^3 angle complemented the obtuse sun angle and made the drops appear red. Did you think it was the spittle from a 3-headed Bugabloobian centipede?

    Jeez! Everything’s an alien conspiracy these days. I suppose spirolina is actually a mind control organism planted here by aliens too! Wait, spirolina? I knew it! Are you serious? I hadn’t heard that one. Wait until they hear about this at the UFO convention!

  10. Evolving Squid

    I was reminded of this…

    Cartman: Eh. I hate those things.
    Kyle: Nobody hates rainbows.
    Stan: Yeah. What’s there to hate about rainbows?
    Cartman: Well, you know. You’ll just be sitting there, minding your own business, and they’ll come marching in, and crawl up your leg, and start biting the inside of your , and you’ll be all like, “Hey! Get out of my you stupid rainbows!”
    Stan: Cartman, what the are you talking about?
    Cartman: I’m talking about rainbows. I hate those friggin’ things!
    Kyle: Rainbows are those little arches of color that show up after a rainstorm.
    Cartman: Oh. RainBOWS. Yeah, I like those. Those are cool.
    Stan: What were you talking about?
    Cartman: Huh? Oh nothing. Forget it.
    Kyle: No. What marches in, crawls up your leg—
    Cartman: Nothing.
    Kyle: —and starts biting the inside of your ?
    Cartman: Nothing!

  11. Star Girl

    Well, at least when Phil figured out why he was seeing the rainbow he didn’t jump out of the shower and run down the street naked shouting eureka. Or did you Phil?

  12. I’ll leave that for your imagination. :-)

    Sorry I missed you at Tucson, by the way; I saw on your blog you were there. But I’ll be at the AAS meeting in DC in January!

  13. I’ll be at the AAS meeting in DC in January!

    Ooh! Ooh! Ooh!
    If I bring my copy of your book, will you autograph it?

  14. Michelle Rochon

    I remember that when I was a brat, I would take the hose and make rainbows in my backyard. :)

    There’s a waterfall not too far from here too, and it’s not rare to see rainbows in the droplets too. No matter really where you are relative to the sun, you can see them.

  15. Jessica

    Very cool! I was driving back from my fiance’s on Sunday while we had a huge wind-and-thunderstorm. And rain. (I hate the weather now, it’s crazy.) About halfway back I saw the sun coming out, sort of, and a lot of fleecy clouds in the sky. There was a vertical rainbow in the clouds! (Cloudbow? It’s been years since I studied clouds.) Funny thing was, though, that the sun was about thirty degrees or so to my right, and the rain/cloudbow about the same to my left. Well above my head, obviously. It was beautiful; wish I’d had my camera and been able to take a picture.

  16. HvP


    It’s often difficult to guess these things from just a description, but I’m thinking you were able to spot a “Sundog”. See if this link looks anything like what you saw:

    They don’t always show a multicolor spectrum in the glare, but the ones that do are very striking. I was lucky enough to see one (actually two, one on each side) a few months ago. It was quite brilliant and kept it’s luminosity for a good 20 minutes.

    They are caused by falling ice-crystalls instead of raindrops like a rainbow.

  17. Blake Stacey


    Thank you very much for linking to the site — both the pictures and the explanations are fantastic!

  18. hale_bopp

    I was flying from St. Thomas to St. Croix on a little puddle jumper and looked out the window and saw a full 360 degree rainbow! After an initial bout of surprise, it made perfect sense that there are equal angles above and below the horizon. We just never see the bottom half because the ground gets in the way.

    So it sounds like Phil saw the bottom half of the rainbow as he was looking down with the Sun high and behind him.

    Oh, but my camera was in checked baggage!


  19. To see a rainbow toward the sun, like a sundog, maybe you just need a refracting material of a certain shape.

    Here’s a double sundog I caught in mist a few feet away one morning in Yosemite National Park:

    The key to that one may have been below-freezing temperatures, creating suspended ice crystals much like you’d get way up in the atmosphere with a typical sundog.


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