Have you seen a perfect halo around the moon recently? Here's why. FacebookTwitterEmail A halo seen around the moon. The halos you see are caused by refraction, or splitting of light.Boy_Anupong/Getty Images 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 almost full moon is refracting through ice crystals in the high thin cirrus clouds over the Bay Area this evening to create a well-defined 22 degree lunar halo," Golden Gate Weather Services meteorologist Jan Null posted on Twitter on Saturday. Light from the almost full moon is refracting through ice crystals in the high thin cirrus clouds over the Bay Area this evening to create a well-defined 22 degree lunar halo. pic.twitter.com/QHwuHymA8O— Jan Null (@ggweather) December 27, 2020