On the night of August 30-31, a rare phenomenon will occur above our heads: a super blue moon. According to NASA, this event only occurs once every ten to twenty years, with the next scheduled for January 2037. This is the third supermoon of the year of four expected.
This name actually combines two phenomena: the supermoon on the one hand, and the blue moon on the other. For the first case, we speak of a supermoon when our natural satellite is at its perigee, that is to say the moment when it is closest to the Earth, at some 363,000 kilometers on average (compared to 384,000 usually ).
We speak of a blue moon when two full moons appear in the same month. This is due to their cycle, which is one every 29.5 days on average. That of August 30 will be the second of the month, the first having been that of the Sturgeon, on the night of August 1 to 2.
This overlap only occurs once every two or three years. The expression “blue moon” does not mean that the star will take on a bluish tint. This is an anglicism emphasizing its rarity, taken from the English expression “Once in a blue moon”, which is the equivalent across the Channel of our “when the hens will have teeth” or “every 36 of the month “.
According to NASA, 25% of full moons are supermoons, but only 3% of them are blue moons. The time interval from one super blue moon to another can be twenty years, but it averages ten years. The next year that will see a super blue moon will be 2037 which will have a first in January, followed by a second in March. Which is even rarer.