Author Topic: What Is a Blue Moon and When Is the Next One? [tonight] (Read 505 times)

240B · « **on:** October 31, 2020, 07:32:54 pm »

timeanddate.com
By Vigdis Hocken and Aparna Kher
Saturday, October 31, 2020

On Saturday, October 31, 2020â€”Halloween, in many countriesâ€”a Blue Moon will shine bright in the night sky. This Halloween Blue Moon, which is also a Micro Full Moon, is October's second Full Moon in many time zones.

What Is a Blue Moon?
There are two different definitions for a Blue Moon. A seasonal Blue Moon is the third Full Moon of an astronomical season that has four Full Moons. A monthly Blue Moon is the second Full Moon in a calendar month with two Full Moons.

The Full Moon on October 31, 2020 is a monthly Blue Moon. October's first Full Moon, and this year's Harvest Moon, was on October 1, 2020.

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How Rare Is a Blue Moon?
For a monthly Blue Moon to take place, a Full Moon must occur at the beginning of the month. This is because the time between two successive Full Moons is approximately 29.5 days, just short of most months in the Gregorian Calendar.

Seasonal Blue Moons take place slightly less frequently than monthly Blue Moonsâ€”in the 1100 years between 1550 and 2650, there are 408 seasonal Blue Moons and 456 monthly Blue Moons. This means that either type of Blue Moon occurs roughly every two or three years.

Blue Moons that are blue are incredibly rare and have nothing to do with the calendar or the Moon's phases but are instead a result of atmospheric conditions. Volcanic ashes and smoke, water droplets in the air, or certain types of clouds can all contribute to a Full Moon taking on a blue shade on rare occasions.

Double Blue Moon
Because of this, February, which has 28 days in a Common Year and 29 days in a Leap Year, can never have a monthly Blue Moon. Some years, February has no Full Moon at all, which is called a Black Moon. A February with no Full Moon happens when January and March have a Blue Moon each.

Known as a Double Blue Moon, this phenomenon is rather uncommon and takes place only about three to five times in a century. We saw a Double Blue Moon in 2018 in most time zones and will see it again 19 years later, in 2037, in many time zones.

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(more)
https://www.timeanddate.com/astronomy/moon/blue-moon.html