It was also very interesting, because just inside the primary bow there were several smaller bows that I do not recall ever noticing before.
Here is what they looked like:
Rainbows have been studied a great deal, of course, and I assumed somebody would have written about these. So, off to the Internet...
It turns out that these "supernumerary arcs" are caused by interference effects, not by simple refraction and dispersion. In fact, https://en.wikipedia.org/wiki/Rainbow#S ... ry_rainbow says that
http://www.atoptics.co.uk/rainbows/supform.htm and the several pages around it have a lot more detail, including fairly detailed descriptions of mathematical simulations.It is not possible to explain their existence using classical geometric optics. The alternating faint rainbows are caused by interference between rays of light following slightly different paths with slightly varying lengths within the raindrops. Some rays are in phase, reinforcing each other through constructive interference, creating a bright band; others are out of phase by up to half a wavelength, cancelling each other out through destructive interference, and creating a gap. Given the different angles of refraction for rays of different colours, the patterns of interference are slightly different for rays of different colours, so each bright band is differentiated in colour, creating a miniature rainbow. Supernumerary rainbows are clearest when raindrops are small and of uniform size. The very existence of supernumerary rainbows was historically a first indication of the wave nature of light, and the first explanation was provided by Thomas Young in 1804.
I found all this to be quite interesting because a) we don't often get to see clear evidence of light wave interference with our naked eyes, and b) I didn't know about any of this earlier.
I hope you are intrigued also.
PS. The Wikipedia article on Thomas Young is a good read also. I don't know if people were more prolific in those days, or if good new ideas were just simpler to think up. In any case, he certainly contributed a lot of them!