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Enlarge image | Double rainbow red July 21, 2015, by Steve Lacy, near Las Cruces, New Mexico.
It is rare to see a red rainbow. I saw only one during my decades of observation of the sky … although, I admit, I live in a place where it does not rain much. I saw my unique red rainbow early one morning, several decades ago, while driving on the dirt road leading from Chaco Canyon to New Mexico. It's such a magical place, and I felt like the magic of the canyon helped create the red rainbow. Not so.
The Cowley of the large website Atmospheric Optics explains that red rainbows are created when the sun is low, so that the blue and green of its rays are weakened by the dispersion during the long journey into the atmosphere. In this way, red rainbows are similar to red sunrises and sunsets. The explained:
The rays of the setting sun and sunrise travel long paths through the lower atmosphere where they are dispersed by air molecules and dust. Blues and short-wave greens are scattered most strongly, leaving the remaining transmitted light proportionally richer in reds and yellows. The result is beautiful sunsets and red rainbows.
Frances Pelletier caught this double red rainbow on February 9, 2016 in Myrtle Beach, South Carolina.
In 2014, the astrophotographer Göran Strand of Sweden kindly allowed us to publish the picture below, which shows a regular double rainbow (if a rainbow, especially a double, can be described as ordinary), followed by a double red rainbow. This illustrates the making of red rainbows. Göran told Earthsky that he had photographed the upper image in the afternoon, with the sun at about 27 degrees above the horizon. He took the picture from below with the sun at 2 degrees above the horizon.
Notice two things in the photo below: the heights of the two rainbows above the horizon and their colors.
The height of a rainbow depends on the sun. The lower the sun, the higher the rainbow. You can see evidence of this by looking at the picture of the red rainbow, taken at sunset. Do you see how high in the sky it is in relation to the other double rainbow?
Enlarge image | Swede Göran Strand captured this double rainbow in 2014 … and took it back soon after, as the sun went down, which became a double rainbow red. Used with permission. Visit Göran's website on astrophotography or his Facebook page.
By the way, are you interested in double rainbows and how rainbows are made regularly? All the rainbows occur when the sun shines through the raindrops. If the sun is behind you and you see the sunlight emerge from several drops of rain at a time, you see a mosaic of light extending in an arc in the sky: a rainbow. There is double rainbow when the sunlight in a drop of water is reflected twice instead of once.
Here are other red rainbow photos from the EarthSky community. Thank you all!
Red Rainbow at Sunset – May 25, 2015 – on Bluewater, Ontario, Canada. Photo of Kelly Schenk.
Rainbow red on Roque del Conde, on the island of Tenerife, submitted to EarthSky by Roberto Porto.
Here's another beautiful red rainbow shot of Jesper Kristensen, a friend of EarthSky Facebook. It's from August 14, 2014. Thanks Jesper.
Conclusion: If you watch a sunset and it rains in the air, turn in the opposite direction to the sun and observe the elusive red rainbow. Red rainbows occur when the sun is on the horizon. They were created for the same reason that a sunset or sunrise looks red. When the sun is low, its blue and green light fades and disperses over the long journey to your eyes across the Earth's atmosphere. The red light goes through more directly. That's … a red rainbow.
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