The Blue Moon will peak this coming weekend – Saturday, May 18 to Sunday, May 19. UK stargazers will see the Blue Moon appear over the horizon at around 10.21pm BST on Saturday. And the Blue Moon’s arrival will coincide with the arrival of this month’s Full Moon, commonly called the Flower Moon.
Full Moon fans should make the most of this astronomical event, as there will not be another chance to witness another Blue Moon for the next two years.
A year has 12 months, and months – or ‘moonths’
EarthSky astronomers Deborah Byrd and Bruce McClure
There are actually two different definitions of Blue Moons in astronomy.
The first describes a second Full Moon to rise within the space of just one month.
While the second refers to the third of four Full Moons appearing within one season.
Amateur astronomers often think of Full Moons as occurring once per month.
However, sometimes a month actually receives two Full Moons because the phases of the moon take precisely 29.5 days to complete.
EarthSky astronomers Deborah Byrd and Bruce McClure explained how this weekend’s Blue Moon will be the third Full Moon of the season.
They said: “A year has 12 months, and months – or ‘moonths’ – have lengths more or less based on a single orbit of the Moon around Earth.
“What we call a season – winters, spring, summer, fall – typically lasts three months, and typically has three Full Moons.
“If a season has four Full Moons, then the third Full Moon may be called a Blue Moon, according to the Old Maine Farmer’s Almanac.
“There was a Blue Moon by this definition on November 21, 2010, another on August 20-21, 2013, and another on May 21, 2016.”
The rarest astronomical event of them all is a monthly Blue Moon and a seasonal Blue Moon occurring in the same calendar year.
This will next happen in 2048 when a monthly Blue Moon in January is followed by a seasonal Blue Moon in August.
This rare combination will repeat itself in the year 2067 with a Blue Moon in March and November.
EarthSky said: “In this instance, there are 13 Full Moon between successive December solstices – but only 12 Full Moons in one calendar year and no February 2067 Full Moon.”
Each month’s Full Moon receives a traditional name tied to what takes place at that time of year.
May’s Full Flower Moon earned its unusual moniker because it occurs when flowers come into season, according to the Farmers’ Almanac.
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