A BREATHTAKING Blue Moon is set to rise in the sky tomorrow night, which falls on the same day as Halloween.

Blue Moons are defined as the second full moon in a calendar month, and are very rare as, according to NASA, there are about 29.5 days between full moons.

The astounding night time display happens seven times every 19 years, which is perhaps where the phrase "once in a Blue Moon" comes from.

This means the next one will be on Halloween in 2039.

What is a Blue Moon?

A Blue Moon is not actually blue - it looks like a grey-coloured full moon which can appear blue if the atmosphere if filled with dust or smoke particles from a volcanic eruption.

Altogether, there will be 13 full moons in 2020, another rarity because most years only see 12.

The growth of knowledge and wisdom within the phases of a woman's life are associated with a Blue Moon in some modern magical traditions.

When are the remaining full moons in 2020?

November 30 - Beaver moon

December 29 - Cold moon