Blue Moon 2019: What is a Blue Moon? Will the Moon really turn blue this week?

The last Blue Moon of the year will peak in brightness on the night of Saturday, May 18. Here in the UK, amateur astronomers will have a chance to watch the May Full Moon reach full illumination around 10.21pm BST. When this happens, the so-called May Flower Moon will be positioned directly across from the Sun. But why is the Moon called blue and does this mean the Full Moon will change colour on the weekend?

What is a Blue Moon?

There are two different definitions of a Blue Moon, both of which refer to a rare Full Moon appearing out of the blue.

The first definition, which also happens to be the more popular tagline, describes a second Full Moon to appear within one calendar month.

The last Blue Moons by this definition fell on the nights of March 31, 2018, and on January 31, 2018.

The next Blue Moon following these guidelines will fall in October, 2020.

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The second definition of a Blue Moon describes the third of four Full Moons to appear in one calendar season.

Maritime astronomer Bruce McClure of EarthSky.org explained: “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 to 21, 2013, and another on May 21, 2016.”

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After Saturday’s event, the next seasonal Blue Moon will peak on the afternoon of August 22, 2021.

According to the Royal Observatory Greenwich, Blue Moons are a fairly rare occurrence – by both definitions – and appear once every two to three years.

The year 2018 was unusual because it had two Blue Moons to appear only two months apart – an incredibly rare combination.

The next time two Blue Moons appear in one year will be the year 2037.

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Will the Blue Moon turn blue this weekend?

Unfortunately, much like a Pink Moon in April does not turn Pink, the Blue Moon will not turn Blue this Saturday.

The Royal Observatory explained: “Cultures around the world, including the Native Americans, have given names to each of the Full Moon, with each typically happening in its own month.

“For example, the Wolf Moon is usually the Full Moon occurring within January.

“With the cycle of the phases of the Moon lasting approximately one month, and there being twelve months in a year, we typically have twelve Full Moons each year.”

source: express.co.uk