View at EarthSky Community Photos. | Soumyadeep Mukherjee in Kolkata, West Bengal, India, caught this rare lunar halo – an odd-radius halo – on August 21, 2021. See the multiple rings? Plus the image has something extra. That’s Jupiter to the left, and Saturn to the right, of the moon.
A rare lunar halo
The image above shows a rare lunar halo. Most halos around the sun or moon are common 22-degree halos. They’re caused by ice crystals in the upper air. The ice crystals are typically plate- or column-like hexagonal crystals. But the multiple halo you see in Soumyadeep Mukherjee’s image above is different. It comes from pyramidal ice crystals.
According to sky optics guru Les Cowley, pyramidal crystals tumble more in the air. And so they usually form only rather fuzzy circular halos. Les’ page on these halos, which are sometimes called odd-radius halos, mentions halos of 9-, 18-, 20-, 23-, 24- and 35-degree radius: multiple rings around the moon.
View larger. | EarthSky friend Greg Redfern of the blog What’s Up? The Space Place captured this odd-radius halo in Virginia on June 4, 2017. He wrote to EarthSky: “I have never seen one like this in 5-plus decades of skywatching.” Les Cowley commented on this photo, “In Greg’s image, we have 9-, 18-, 20- and 23-degree radius rings compared to the common 22-degree halo … Note the bright spots above and below the moon on the inner 9-degree halo in Greg’s photo, plus the bright areas to the moon’s left and right on the 18-degree circle [see a diagram here]. These are the pyramidal crystal equivalents of paraselenae, or ‘moondogs.'” Thank you, Greg and Les! Image via Greg Redfern.
Bottom line: Photos and info about multiple halos around the moon – caused by pyramidal ice crystals – called odd-radius halos.
Our Editor-in-Chief Deborah Byrd works to keep all the astronomy balls in the air between EarthSky's website, YouTube page and social media platforms. She's the primary editor of our popular daily newsletter and a frequent host of EarthSky livestreams. Deborah 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. 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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