As the saying suggests, a blue moon is a rare event. This weekend’s full flower blue moon is even rarer still, happening only every dozen or so blue moons.

But despite what its name suggests, this full moon is not actually blue. The name simply refers to the fact that it is the fourth full moon of the season, when typically there are only three full moons in a season.

In 2019 there has already been a blood moon, a pink moon and a super worm moon – each named (in these cases) after its colour or occurrences that take place at the time of year the full moon appears (a “worm” moon is named thus as it comes at time small creatures – such as worms – emerge from the ground, signifying the end of winter).

The flower moon, which is set to rise at dusk on Saturday 18 May, is appropriately named after the flowers that bloom in the month of May.

The next blue moon won’t occur again until 2021, so astronomers will be hoping for clear skies this weekend.

Super worm moon - last supermoon of 2019 in pictures Show all 10 1 /10 Super worm moon - last supermoon of 2019 in pictures Super worm moon - last supermoon of 2019 in pictures Worm moon rises over the Karancs Hills in Hungary EPA Super worm moon - last supermoon of 2019 in pictures Worm moon over the Empire State Building in New York Reuters Super worm moon - last supermoon of 2019 in pictures Worm moon over Los Angeles, California AFP/Getty Super worm moon - last supermoon of 2019 in pictures Worm moon rises over the Galicia Massif mountains in Spain EPA Super worm moon - last supermoon of 2019 in pictures Worm moon over Nicosia, Cyprus EPA Super worm moon - last supermoon of 2019 in pictures Worm moon rises over the Santiago de Compostela cathedral in Galicia, Spain EPA Super worm moon - last supermoon of 2019 in pictures Worm moon rises over silhouettes of the Beatles in Liverpool PA Super worm moon - last supermoon of 2019 in pictures Worm moon over the Guggenheim Museum in Bibao, Spain EPA Super worm moon - last supermoon of 2019 in pictures Worm moon rises near Encinitas, California Reuters Super worm moon - last supermoon of 2019 in pictures Worm moon over Los Angeles, California AFP/Getty

This weekend will also see a number of other astronomical events, according to Nasa.

“By the morning of the full moon on 18 May 2019, as morning twilight begins, Jupiter will appear in the south-southwest about 23 degrees above the horizon and Saturn will appear in the south about 30 degrees above the horizon,” the space agency said in a statement.