Stargazers in the Gulf may have noticed something unusual on Saturday night: the unique halo around the moon.
Twitter is very lively. One user wrote: “The moon is out.” Another wrote: “The moon looks crazy tonight.”
What caused it?
A local meteorologist, Jan Null, said on Twitter: “Tonight, the light from the near full moon is refracted by ice crystals in the thin cirrus clouds over the Bay Area, creating a clear 22-degree halo.”
Null shared a photo of this phenomenon on Twitter, showing the bright halo surrounding the moon in a dark sky.
Officials from the National Weather Service stated that the halo is “a ring or light formed around the sun or moon as the sun or moonlight refracts ice crystals present in the thin veil of the cirrus clouds.”
Meteorological service officials said that this is an optical effect that occurs when the atmosphere is “right”.
Yes, this is the moon ring or lunar halo. This effect occurs when light is refracted by ice crystals in thin, tall clouds called cirrus clouds.
-NWS Bay Area (@NWSBayArea) December 27, 2020
“In the atmosphere, under certain conditions, water droplets and ice crystals can act as prisms, allowing us to see the various colors that make up visible light,” the meteorological official explains on their webpage halos and other forms of optical effects. “It is precisely because of these characteristics that we can obtain various atmospheric optical effects.”
The halo was noticeable on Saturday night, when it was mostly sunny and dry in the bay area, but rain is expected on Sunday and Monday.
Tonight, the light from the almost full moon is refracted through ice crystals in the high and thin cirrus clouds in the Bay Area, forming a clear 22-degree halo. pic.twitter.com/QHwuHymA8O
-Jan Null (@ggweather) December 27, 2020
Lauren Hernández is a writer for the San Francisco Chronicle. Email: lauren.hernandez@sfchronicle.com Twitter: @ByLHernandez
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