SAN FRANCISCO—There will be a centuries-rare blue moon on Halloween this year, exactly halfway through fall. The blue moon, defined as the second full moon in any particular month, will be visible in all time zones, reaching peak illumination at 7:51 p.m. Pacific Daylight Time and best visible in the Bay Area as soon as 6:11 p.m. on the western horizon. The celestial occurrence is colloquially referred to as a Hunter’s Moon in the Old Farmer’s Almanac, which references times when hunters used moonlight to hunt in preparation for winter. 

While the last blue moon occurred on March 31, 2018, a blue moon on October 31 has not been observed since 1944, and won’t occur again for 19 years according to the Metonic cycle; hence the phrase “once in a blue moon”. The year of 2020 additionally includes 13 full moons instead of 12, which only happens every two and a half years. The next blue moon will occur on August 22, 2021.  

October’s first full moon, referred to as the Travel Moon, Dying Grass Moon, or Harvest Moon, reaches peak illumination at 2:05 p.m.  

There is a possibility that both of October’s coming full moons will appear orange and, as a result of their location lower to the horizon, they will appear larger than normal due to the optical illusion provided by their near-superposition on tiny-appearing buildings of the skyline.

Additionally, 3 meteor showers will transpire between the full moons, including one that’s known for “spitting fire”, Patch reports. 

Fall back occurs the day after the blue moon, November 1, marking the end of daylight saving time.