Supermoon: what is it?

The term “supermoon” was originally coined by astrologer Richard Nolle in 1979 who sought to link full moons and new moons closest to Earth during the year with natural disasters. There is therefore nothing scientific about this, but it is clear that since the 2010s, the expression has experienced a real craze, in particular through the Nasa and several Anglo-Saxon media who do not hesitate to use and abuse superlatives. Probably in order to capture more public attention on a fairly common celestial spectacle.

Because a supermoon is none other than a Full Moon of perigee. That is to say a Full Moon which occurs when our natural satellite is at the point of its orbit closest to the Earth (the orbit of the Moon around the Earth is elliptical: it varies between 356,000 kilometers and 406,000 kilometers). Which is not as rare as one would like to believe. But the term seems to be gradually becoming commonplace.

There is no official definition of a supermoon.

“Although there is no official definition of a supermoonexplains the Paris Observatory, it is tacitly admitted that the distance of the star from the Earth, at the time of the full Moon, must be less than 356,600 kilometers. » However, many times Full Moons more than 356,600 kilometers away have been called supermoons.

Does this really change anything? Visually, it is difficult to perceive a difference with the other full moons of the year. Indeed, the apparent size of our satellite in the sky varies between 0.48 and 0.56 degrees (see image above) depending on its position in its orbit. A true “supermoon” can appear 14% larger than a full moon that coincides with theapogee. But it remains quite small in the sky and it is not easy to be able to distinguish the difference. A “supermoon” therefore does not mean that a Giant moon will rise from the horizon.