There's an interesting site Atmospheric Optics - http://www.atoptics.co.uk/ - that has pages on understanding the various phenomena related to how light can interact with our atmosphere - rays, rainbows, etc.
What prompted me to look this up was a Tracy Art League gentleman who stopped into my last Beginning Photo class session on Thursday evening in the neighboring classroom. My laptop's background image is a 5-minute exposure of a wintertime dry Yosemite Falls under full moonlight, last January.
Rather than simply tell all the details of the "when" of this image, I asked him to study it and offer thoughts on it.
We ventured further into other Yosemite scenes, including last month's afternoon break-in-the-storm rainbow against Yosemite Falls.
Whether by vocation or avocation, this gentleman knew his atmospheric lighting phenomena, and mentioned things like "Alexander's Dark Band" between the primary and secondary rainbows, and the "Supernumeraries" just inside/below the primary bow...specific details of a raonbow I wasn't familiar with.
This site includes much more than an explanation of physics and geometry of rainbows. But, this was an interesting place to start.
Enjoy your explorations, and may the findings and rewards prove worthwhile.
Best Wishes...
Richard D. Beebe
...photographer -
......N. California
...photography instructor -
......Grand Theatre Center for the Arts,
......Tracy, Calif.
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