Full featured double rainbow in Wrangell-St. Elias National Park, Alaska by Eric Rolph
I was in my twenties before I ever saw a double rainbow. I was on my way to meet some people in a pub in London's King's Cross and I got drenched on the way. More drenched than usual or necessary because an amazing double rainbow appeared and I remember there were quite a few of us looking at it in surprise and a several people commented on its double-ness.
At the time (mid 90s) there wasn't that much information about double rainbows on the web but I learned that it was a real enough phenomenon and we'd not imagined it. After that I found I kept noticing them, even if the second rainbow was so faint it was barely visible - you have to look near it rather than at it directly. I also spotted that the second one was always reversed and have since found out the reason for that.
Wikipedia has a very detailed page on rainbows and also mentions 'supernumerary rainbows' which are apparently 'infrequent' though I see those often enough.
I now see double rainbows all the time, two this week alone. I must have stared at umpteen rainbows as a child, and with my parents and others who all had experience of rainbows. No-one ever mentioned the possibility that there could be a second one.
I can't believe that there have been any dramatic atmospheric changes in the last 30 or so years that would account for the sudden appearance of double rainbows so my theories are as follows ;-)
- Brightly visible double rainbows are a bit rarer than brightly visible single ones (I've never seen the second bow appear as brightly as the first) so they're easily missed
- My parents and family friends weren't scientists (or artists) and perhaps those are the people likeliest to tell you about double rainbows, where they're otherwise not that visible.
- My parents were pretty sensible and didn't tend to stand around staring at the sky when it was wet
- Given (1) it probably took a bit of time for news to get out about the second bow and coupled with the fact that info is easier to find online about them now I can imagine that people see one, google it, and share the info with their friends who then know to look out for it the next time there's a rainbow.