I recently received a question from a reader asking if all rainbows are actually round. I have to admit that my initial response was “no” because I’ve never heard of a completely circular rainbow. However, by definition, rainbows could potentially be round. The reason we don’t see round rainbows is that the bottom of the bow is cut off by the horizon, which leaves us with the arc that we usually associate with rainbows.
Most of us have seen double rainbows at some point in our lives. These are actually called the primary and secondary rainbows. The primary rainbow usually has red on the outside and blue on the inside, while the secondary rainbow has red on the inside. There is also a type called the supernumerary rainbow, which can sometimes appear inside the primary bow. So theoretically, you could see three rainbows at one time.
The brightness and intensity of the rainbow depends on a few different things including the type of precipitation that is falling. Is it rain or drizzle or even just a cloud? What is the size of those raindrops? The angle of the sun makes a difference in how the rainbow appears as well.
There are a couple more components that enter into the process, and they are very personal. First, the apparent center of the rainbow is technically the shadow of the observer’s head since the sun must be behind the observer in order for him to see the rainbow. Second, because each person views a rainbow from a slightly different angle and our eyes process the light slightly differently as well, each person sees a slightly different rainbow. The second is my personal favorite because it means we technically each get to claim our very own rainbows.