David Lamberti caught this circumzenithal arc in 2019. Notice the kite in the tree! He wrote: “It was a beautiful January day in southeast Michigan. I looked up, and there it was, a beautiful circumzenithal arc. It was enormous, and the colors were very deep. It faded within 5 minutes.” Thank you, David!
People who look up might occasionally see the rainbow-like arcs depicted in the photos on this page. They’re called circumzenithal arcs, and they’re not really rainbows. Instead, they’re caused by ice crystals in the upper atmosphere. These arcs are related to the frequently seen halos around the sun or moon. Les Cowley of the great website Atmospheric Optics says of these graceful and colorful arcs:
The circumzenithal arc, CZA, is the most beautiful of all the halos. The first sighting is always a surprise, an ethereal rainbow fled from its watery origins and wrapped improbably about the zenith. It is often described as an ‘upside-down rainbow’ by first-timers. Someone also charmingly likened it to ‘a grin in the sky.’
Look straight up near to the zenith when the sun is fairly low and especially if sundogs are visible. The center of the bow is always sunwards and red is on the outside.
View at EarthSky Community Photos. | Auke Schilder in Tervuren, Belgium, caught this circumzenithal arc on November 26, 2022, and wrote: “In this photo, the sun is behind the trees at the bottom-centre of the photo. I’m 50 years old and I had never seen one of these before.” Thank you, Auke!Circumzenithal arc captured by Tony Bowman in Surrey, England.Patricia Chambers caught this circumzenithal arc from Potomac, Maryland, on August 5, 2016. She wrote: “It had rained not too long before I took the pic. I went out in my deck and saw an unbelievable sight – an upside-down rainbow! I was truly mesmerized … Enjoy!”Circumzenithal arc captured September 16, 2015, in Lancashire, UK, by Amanda Cross.Dan Szulewski captured a circumzenithal arc from Hermiston, Oregon, on June 22, 2014.Dorothy caught this circumzenithal arc on January 9, 2014.Julie Gurnhill caught this one on February 27, 2013.John Gravell captured this circumzenithal arc from Boston on October 17, 2012.Duke Marsh caught this circumzenithal arc on October 3, 2012, from New Albany, Indiana. Thanks, Duke.Rene Pennings captured this circumzenithal arc on May 21, 2012.A lovely circumzenithal arc amidst high clouds by Dudley Williams on December 18, 2011.Andrew R. Brown caught a circumzenithal arc in Ashford Kent in the UK, on November 19, 2010.
Bottom line: When you see what looks like an upside-down rainbow, you’re likely seeing a circumzenithal arc. It’s related to the halos often seen around the sun or moon, caused by ice crystals in the upper atmosphere.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.
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