No Rainbows Without Rain

Yesterday I saw the most perfect rainbow I have ever seen in my life.  It was a full 180 degrees, clearly visible, from horizon to horizon.  I was driving at the time, and so unable to take a picture, and by the time I could stop the angle or the light was wrong, and only a fraction of it was still in view.  I do miss the weather being mostly comfortable every day in SoCal, but there is a real beauty to the passing of the seasons and the unique sky and landscapes created by harsher weather.  I think you can especially appreciate this if you are into winter sports (Courtney and I love skiing).

Back to the rainbow, I think I know more than the average bear about light and optics (though I have met more than a few people who make my knowledge appear paltry) and yet I found myself puzzling yesterday, as I drove, about the fact that a rainbow always seems to describe a portion of a perfect circle.  After a little internet research today (so if this is incorrect, don't blame me, blame my generations over reliance on the internet as a source of valid information) I found the reason why.  Small raindrops are as close as possible to being perfectly spherical.  Some of the sun's light will bounce off of these raindrops, and it will always bounce at almost exactly 42 degrees.  Why almost and not exactly, you ask?  Well that is precisely what creates the rainbow.  The angle varies slightly based on the frequency of the light, which as you may know determines the color of the light.  So red light, having a very low frequency, is on one end of the spectrum, and violet light, being very high is on the other.  Essentially, a rainbow is the result of millions of individual raindrops acting as tiny prisms, where you can only see the reflected light of drops that are approximately 42 degrees off of a line between your head and your heads shadow, forming a perfect circle cut off only by the horizon.  Consequentially, that means that the rainbow appears, to every single individual observing it, to be perfectly centered on them!

If you were looking out on a rainstorm from the top of a very tall building or tower, near dusk, the rainbow could appear as a mostly complete circle broken only by the shadow of the building.  Pilots flying have reported on numerous occasions seeing a complete circle of rainbow when conditions are right.

Thinking about light is part of my job as a sustainability consultant that has always brought me great joy.  Optics are fascinating to me for many reasons, and natural daylighting is a very important part of sustainability.  Just a quick tidbit, did you know that the sun produces energy at all frequencies, but the vast, vast majority of that energy is produced in the spectrum of visible light?  Energy above this spectrum (UV) is almost all damaging to tissue.  This blew my mind the first time I heard about it.  It is one of those facts that seems just too perfect, as if the universe was made for us.  Of course, the truth is that we evolved into our current condition to fit our environment; we were made for the universe.

With all this knocking around in my head, I have decided to post some basic tips about maximizing daylight in your home or office, working with the conditions you have.  Not tonight however, I have done enough blogging for today.  Until next time, good night, and I hope that you get a chance to wonder at the light a little tomorrow.