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'Tis the season for dramatic, sky-filled rainbows!

Rainbow shines over the Edmonds waterfront. (Photo: Michelle Sistek)

There have been several photos in the past few weeks of huge, arcing rainbows that seem to fill much of the horizon, even bright enough to create double rainbows as well. But did you know that this time of year is the best time to see rainbows?

It's not all based on climate, although being in the rainy season surely helps get half of the needed ingredients for rainbows. But it's because of the low sun angle.

According to the National Center for Atmospheric Research, the center point of a rainbow is as far below the horizon as the sun is above it. So when the sun is higher in the sky, you only see the top part of the arc, and the rainbow isn't as expansive.

To get those dramatic, large arc rainbows, the sun has to be closer to the ground. In the spring, summer and early fall, the sun spends a lot of time much higher in the sky. There's even a period during the summer where the sun angle is so high you can't see rainbows around lunchtime (because the rainbow would be projected on the ground instead of on the horizon).

The magic angle is 42 degrees, and as long as the sun is below 42 degrees off the ground, you can see a rainbow. But as the sun gets even lower, you can see even more of the bow -- near sunset you'll get nearly the entire semi-circle.

Near the winter solstice, the sun at most gets to about 18-25 degrees above the horizon, meaning not only are rainbows possible all day long, they're usually pretty dramatic.

Case in point, the photos we have in the gallery above.

Sometimes, they even get creative. Check out this photo taken by Chris Erikson:

This is called a "reflection rainbow" -- caused by a body of water (just beyond that hill) reflecting the primary rainbow back into the sky. You can see more details on how that's formed at the Atmospheric Optics site.

So when you see the sun peek out amid the post stormy showers this winter, look for the rainbow, especially in the morning and late afternoon. I'll bet it'll be pretty dramatic!

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