Jesse Ferrell

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What is the Best Time of Day For a Rainbow?

June 10, 2010; 10:03 AM ET

What's the best time of day to see a rainbow? You've probably heard "early morning or late evening." But why? The height of the rainbow above the horizon depends on the time of day, or more specifically the angle of the sun.

You can read a better explanation on the Atmospheric Optics website but basically when the sun is 42 degrees up, the rainbow will be on the horizon or close to it. If the sun gets higher, the rainbow will be below the horizon and you won't be able to see it. Here's a graph of sun angle versus rainbow height:

What does this mean to you? Well, it depends on the time of year and your location, which is why I didn't put clock times on the x-axis. If you're on the Equator at the summer solstice where the sun rises at 6 AM and sets at 6 PM, the sun will be at 90 degrees at noon, don't expect to see a rainbow between 9 AM and 3 PM. Your results may vary; that's why people say "early morning or late evening." What they really mean is, the closer to sunset or sunrise, the better.*

You don't see that many low-horizon rainbow pictures because rainbows at that height are more likely to be obscured by trees, hills or buildings, but we did get a couple recently here at AccuWeather.com, one on our Photo Gallery on May 8th in Oregon, shown above, and another on our Facebook Page on June 3rd in Connecticut. We also received this relatively-low rainbow (with Supernumeraries!) yesterday from New Hampshire.

Would you have a better chance of seeing a rainbow in the winter, or further north? The sun angle would be lower, perhaps always below 42 degrees if you were far enough north, but the day would also be shorter. There probably is a "sweet spot" for rainbows but I'll leave that up to better scientists than me, because it gives me a headache to think about it. I've sent an email to Les Cowley, Atmospheric Optics expert. If you know anyone who could answer this question, hit me up on Facebook.

*I tried to fact check myself by using the NOAA Solar Calculator but please check my numbers and Facebook me if you see discrepancies. According to that calculator, I can't currently see rainbows in Central PA between 8 AM and 3 PM, but in January I could see them all day. Check out your own (look for the EI value to be below 39). I suppose you could argue that sunlight may not be as strong right at sunrise or sunset, which could weaken the rainbow.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Jesse Ferrell
Jesse Ferrell's WeatherMatrix blog covers extreme weather worldwide with a concentration on weather photos and Social Media.