triple rainbow

The Science Behind the Triple Rainbow

Lan Ma

So maybe you’ve seen a double rainbow or two before, but what about a triple rainbow?

It turns out, while it definitely looks that way, what the Bay Area saw Sunday was something known as a reflection rainbow. More on that below.

This certainly caught the eye of our intrepid weather-watching, photo-taking viewers Lan Ma and Roberto Khamseh (see photo gallery).

While triple rainbows (known as tertiary) are possible, these photos show a slightly less are but still unique weather phenomenon beyond the double rainbow in view.

As light is reflected through water droplets, a rainbow is formed and when leftover light comes back for a second reflection a double rainbow can occur.

Photos: The Science Behind the Triple Rainbow

Each pass becomes progressively fainter so being able to see one requires usually a darkened background (darker clouds) and having strong light passage usually requires slightly larger and uniform droplet sizes.

However in this case, as the photos where taken in Newark, CA by Lan Ma https://twitter.com/LanMisty there’s a slightly different explanation to what’s happening and it has to do with the bay water below.  These are better known as “reflection rainbows” when light can bounce off a bay and heads back through the water droplets again. 

As noted in this article under somewhat similar weather circumstances in New York https://www.nbcnewyork.com/news/local/quadruple-rainbow-photo-4-rainbows-new-york/1006580/.

Regardless of the science involved, if you’re lucky enough to have seen it for a time in the Newark, CA area Saturday evening you can consider yourself pretty lucky as reflection rainbows off the bay aren’t seen all that often and are guaranteed to light up social media.

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