If you recently saw a moon in the Bay sky, there is a fun scientific reason for the celestial face.
“The light of the near full moon breaks through ice crystals in the high thin cirrus clouds over the Bay tonight to create a well-defined 22-moon halo,” meteorologist Jan Null of Golden Gate Weather Services posted on Twitter on Saturday.
Although it is remarkable to behold, ray circles actually occur more than rainbows.
Moon halos occur when there are high, thin clouds over the sky. The clouds were filled with innumerable ice crystals, each shaped like a small hexagon. Like a million small lighthouses, the crystals break apart lightly. The light breaks 22 degrees, which is the ray of the lunar halo.
The phenomenon is visible during the day as well as at night, and Bay residents who looked up on Saturday night were lucky enough to experience it.
The thin clouds are expected to be replaced by stormy clouds later Sunday. A bit of rain is expected in the Bay overnight, and it is cold enough that snow at higher altitudes is possible.
“Because of the speeds that are expected to be above / freezing above 4000 feet, some of the highest altitudes can see some small snow accumulations!” tweeted the Bay National Weather Service Sunday morning. “We’ll keep a close eye on the Santa Lucia and Diablo Ranges tonight.”