Monday, June 6, 2016

Yard Rainbows - From Simple Summer Science to High School Physics (and beyond) in the Backyard

I was out watering the yard one evening, over the weekend, when I noticed what looked like a double rainbow in the sprinkler (color enhanced above, to make it show up better).  At least, at the time I thought it was a double rainbow (thus the photograph).  Now I'm not so sure, maybe it's a twin bow instead.  I can't quite tell if the colors are reversed in the fainter bow, and the colors have to be reversed for it to be an actual double rainbow.

Did you know that?  I sure didn't - until I stumbled onto Walter Lewin's For the Love of Physics, from the End of the Rainbow to the Edge of Time - A Journey Through the Wonders of Physics.  He includes an entire chapter on rainbows, filled with all kinds of interesting details about refraction, reflection, destructive and constructive wave interference, Snell's law, and how to spot all kinds of rainbows.

I think they're interesting facts, anyway (you can catch a lecture of his on the same subject and containing almost all the same information on YouTube, as well).

The children didn't care as much for the chapter, or the lecture.  They are of the opinion that too much math or science takes all the magic out of the phenomenon.

They were quite happy though, to take some of their new found knowledge (yes, I did make them sit through the whole thing :) outside to try making circular rainbows at noon - by spraying a mist of water up into the air, from a hose held at chest level, putting them in the center of the mist, at a vantage point to see pretty much the entire circle of color (which is very cool, by the way).

My camera is not waterproof (and was apparently set on a strange light setting) so I stayed out of the center of mist with it while D (age 13) took a look at the rainbow.  Later in the day though, I was able to catch the multiple bands of color G (age 17) created with the mist setting, in the evening sun.  Those are not double rainbows either, but supernumerary rainbows instead (at least I think they are).

As, to the double rainbow we were hoping to see, but were never quite sure of, we found an experiment...

...that helped us create our own, inside, with a clear mug of water, held at a 42° angle above the eye line to the beam of light (from a flashlight on the table behind us) refracting through the water in the cup and reflecting off the back side, to see the initial spot of rainbow, then adjusting the angle slightly, until we had two (with a few extra reflections)...

...a primary band - with the red on top, and a secondary - with red on bottom.

The video linked above gives a much clearer explanation of the experiment.  We tried it with a fish bowl too, but found lack of handle made it cumbersome to lift up and down in the light. 

At any rate, the lawn is now well watered, we had a lovely science lesson, ultimately found our double rainbow, and even the least science minded of us has a better appreciation for the complexities of rainbows (and physics) - wherever we might find them.

Have you taken a look to see what's in your yard today?


  1. That double rainbow experiment is fantastic!

  2. Thank you so much for the link to the physics book - I have just ordered it for my son today! Do you know of any other physics books in a similar format? Thomas has finished GCSE but doesn't start A level for another two years and I am know he would love to keep his physics fresh whilst he waits :)

  3. I really just stumbled into this one. The author does seem to have a number of lectures on YouTube though - that all look pretty interesting.

  4. Very cool rainbow science! I'll have to encourage my son to check out that book and the YouTube videos for sure.

  5. I read the other day light has to hit a rain drop at 30 degrees to form a rainbow. I'll have to explore this in more detail later.

  6. This is very fascinating. I have to save this video for when A is a bit older, but I think she will find it intriguing then...