The waxing moon was cloaked in a haze of deep auburn Wednesday night. Last month, the darkened skies over the Bay Area turned an ominous shade of orange.
They’re part of the same deeply troubling climate trend, scientists said: climate change spurring intense wildfires spurring air pollution.
“That moon was a signpost that the fires are putting tremendous amounts of pollution into the air,” said Ronald C. Cohen, a professor of earth and planetary science at UC Berkeley.
The red color was caused by smoke particles — and is not to be confused with a blood moon, the colloquial term for the reddish tinge of a lunar eclipse. All eyes will be on the full moon Thursday night to see if the phenomenon repeats itself.
The high volume of pollutants and debris spewed from the nearby Glass Fire scattered particles the human eye would normally have perceived as blue, casting the moon in an otherworldly red.
The smoke blanketing Bay Area skies Wednesday night mimicked the conditions that typically exist during a vivid sunset.
As the sun descends at sunset, light from the sun passes through a greater distance of the Earth’s atmosphere to reach the human eye. The blue is scattered away, and the remaining long wavelengths make the sun look red.
“Smoke particles are better at scattering than air, so the same effects are stronger and the sun or moon can look red when we look directly at them,” said Cohen.
The crimson moon may have looked pretty, but to Cohen it was just one more ominous indicator of poor air quality cloaking the Bay Area.
“Even if there wasn’t COVID, this would be the time to wear a mask,” he said.
Nora Mishanec is a San Francisco Chronicle staff writer. Email: nora.mishanec@sfchronicle.com Twitter: @NMishanec
Read More: Air pollution from wildfire smoke creates crimson moon, worrying scientists