If you saw an angelic moon in the sky of the Bay Area recently, there is an interesting scientific reason for the celestial scene.
Golden Gate Weather Services meteorologist Jan Noll posted on Twitter on Saturday: “Light from an almost full moon is refracted by ice crystals in the thin clouds high over the Gulf this evening to create a well-defined lunar halo of 22 degrees.”
Although great to look at, halos are actually more common than rainbows.
Lunar halos occur when there are high and thin clouds across the sky. Clouds are filled with countless ice crystals, each shaped like a tiny hexagon. Like a million small lighthouses, the crystals refract light through each other. The light is refracted by 22 degrees, which is the radius of the moon’s corona.
This phenomenon is visible both during the day and at night, and Gulf residents looking up on a Saturday night were lucky enough to experience it.
The fluffy clouds are expected to be replaced by storm ones later on Sunday. Little rain is expected in the Bay Area throughout the night, and it is cool enough that snow is possible at higher altitudes.
“Since temperatures are expected at / near freezing above 4,000 feet, some of the higher altitudes have the potential to see some slight snow accumulation!” The Bay Area National Weather Service tweeted Sunday morning. “Tonight, we’ll be watching Santa Lucia and the Diablo Ranges closely.”
