A Rainbow in Striped Air

Last Friday I was meeting some friends at a restaurant not far from where I used to work. It was a get-together of people who used to work together, all of whom have managed to keep in touch and remain friends, even though for some it has been years since we last had the same employer.

A friend had a special request for me to bring a dozen cupcakes from Sanitary Bakery. Nobody at my old workplace has had anything from there since I left at the end of February. I was happy to oblige.

I was 35 minutes into the 40 minute drive to the restaurant, picking my way through a thunderstorm and pleased with myself for being 15 minutes early, when a call came through on my hands-free cell phone. I pressed the button to take the call.

It was my mom. "You forgot the cupcakes."

Aw, crap.

We came up with a plan: I would turn around, and she would saddle up her car, and we would meet somewhere in between. That put us in the parking lot of a hotel in Pittston.

The rain was just ending and the sun was coming out as I pulled into the lot to wait. Rainbow?, I thought. I turned to look at the antisolar point and then out the specified radius for any telltale light patches. And I saw this:


I have never seen anything like this, though I imagine it's not unusual: a rainbow cut by crepuscular rays*, "shadow rays" emanating from the sun, or rather areas where sunlight is blocked by obstructions like clouds. I have seen some stunning crepuscular effects in the past, but I don't remember ever seeing them associated with a rainbow before.
The rainbow was pretty large; at the time I was seeing it it was about 6:45 P.M. on July 6. That places the sun low in the sky, so the antisolar point (the center of the rainbow, marked by an imaginary line going from the sun through the back of the viewer's head, through the eyes and to the shadow of the viewer's head on the ground) wasn't too far below the horizon. Much lower and the sun would be blocked by low clouds in the West and the rainbow would not be visible.
Atmospheric optics are really an amazing thing. Nature and the world around us can be beautiful, and knowing what you're looking at and looking for enhances your appreciation of that beauty. It is one thing to look up at the sky with wonder, and it is quite another to look upon it with an analytical eye. The trick is to do both at once.
So because I forgot a box of cupcakes, I got to see this amazing rainbow, and so did my mom. And now, so have you.

Recommended reading:
E.C. Boyer, The Rainbow
M.G.J. Minnaert, Light and Color in the Outdoors
*Technically these were "anticrepuscular rays". "Crepuscular rays" are "sunbeams", "anticrepuscular rays" are shadows. Whenever you see one, you're effectively seeing the other next to it.
Title Reference: "A Rainbow in Curved Air", album by Terry Riley, used as background music throughout the original radio program of The Hitchhiker's Guide to the Galaxy.