A celestial body is said to be at perigee when it has reached on its elliptical orbit the point farthest from its parent body..
As the Moon moves along its eccentric orbit, during a month its distance from the Earth varies from about 356 000 km to 406 000 km.
Although there is no official definition of the super Moon, there is a tacit agreement that this object’s distance from the Earth is less than 356 600 km.
A "real" super Moon for the New Year
On Sunday, December 3rd 2017, the Moon will be at perigee, a little after full Moon, at a distance of 357 492 km.
Just 1 500 km away from the critical distance of "356 600 km" it can justly merit the label of the "super Moon".
On the other hand, the full Moon of January 1st 2018 is likely to be a "real" super Moon, at a distance of 356 564 km from the Earth at perigee.
On January 31st 2018, the Earth-Moon distance will be 358 995 km.
The full Moon, thrice in succession, will appear much larger than usual, so that it will be much easier to distinguish with the naked eye the dark areas and the various contrasting regions.
Super Moon or ultimate Moon?
During the XXIst century, one will have to wait until November 25th 2034, to see the full Moon closer than 356 500 km.
And on December 6th 2052, the full Moon will be at its closest ever to the Earth, at a distance of 356 425 km.
Note that during the last two thousand years, there have been only two ultimate Moons (at distances of less than 356 400 km), just over ten km from this renowned minimal Earth-Moon distance:
- on December 19th 796 : 356 366 km
- on January 4th 1912 : 356 375 km
These particular "ultimate" Moon perigees could even be dubbed "proxigees".
Proxigees are becoming increasingly rare!
It turns out that the ultimate Moons are becoming increasingly rare, due to the reduction in the eccentricity of the terrestrial orbit.
In the future, one will have to be increasingly patient to see these exceptional super Moons. The next ultimate Moon is predicted for... January 1st 2257, at a distance of 356 371 km.