If you’ve seen an angelic-looking moon in the Bay Area sky lately, there’s a fun scientific reason for the celestial sight.
“Light from the near full moon will break through ice crystals in the tall thin cirrus clouds over the Bay Area tonight to create a well-defined 22-degree lunar halo,” Golden Gate Weather Services meteorologist Jan Null wrote on Twitter on Saturday.
While it is remarkable to see, halos are actually more common than rainbows.
Moon halos are created when there are tall, thin clouds in the sky. The clouds are filled with countless ice crystals, each shaped like a small hexagon. Like a million little lighthouses, the crystals shatter every light. The light refracts 22 degrees, which is the radius of the moon’s halo.
The phenomenon is visible both during the day and at night, and Bay Area residents looking up Saturday night were lucky enough to experience it.
The thin clouds are expected to be replaced by stormy clouds later Sunday. A little rain is expected in the Bay Area at night, and it’s cold enough that snow can fall at higher elevations.
“As temperatures are expected to be at / near freezing above 4000 ft, some of the highest altitudes have the potential to see some small snow build-up!” The Bay Area National Weather Service office tweeted Sunday morning. “We’re keeping a close eye on the Santa Lucia and Diablo Ranges tonight.”