The Full Circle of the Rainbow

Did you know that rainbows aren’t just arcs? The rainbow is really a complete circle (well, a cone if we want to be really picky); the catch is that you’re usually not in a position to actually see the whole thing, because you need sufficient mist to reflect the sunlight back in just the right way all along the entire 42 degree circle of a rainbow. And since most rainbows are cast by distant mists and we’re usually standing on the ground, that means we usually don’t get to see even a full arc, let alone the bottom part of the bow.

rBut what if you were flying? What do birds see? Here’s an ultralight flight over the island of Oahu, with a magnificent full circle rainbow almost directly below them; if the sun is this high in the sky, this is rainbow you pretty much can’t see any other way than getting above the droplets.

This drone footage from Ireland shows a bow that is easily visible from the ground, starting on the ground and then rising up until the bow is complete. It’s a magnificent demonstration of how a rainbow changes as your perspective on it changes.

Actually, you don’t even have to be flying. All you need is a high viewpoint and a lot of mist. Niagara Falls, Ontario’s Skylon Tower provides a great high viewpoint next to a near perfect mist-maker, Niagara Falls:

And, y’know? I kind of lied about the “high viewpoint”. If the mist is close enough to you, just standing up is enough, if the sun is low. (Remember: the center of the rainbow is always directly opposite the Sun.) I don’t have any pictures of this, because I was driving at the time, but one day probably seven or so years ago I was driving back from my brother’s birthday party. A wicked storm had just blown through the area while we were in the party, so we were surprised to come out to find wet roads and a brilliant sun. Driving back, roadspray kicked up just the right kind of droplets, and alongside the car I could see the bottom of the rainbow. It was magical. Less magical was getting home and discovering what the hail had done to my siding, but I do wish I had pictures of that rainbow. You can simulate that sort of thing yourself this summer, when you go out to water your lawn, although it’s tough to get enough droplets to cast a full bow. Move the spray around, and “paint” more of the rainbow. It’s a small-scale way of demonstrating the same effect, and great fun for children. 😉

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