On Tuesday 19 December 2017, at 1.28 am GMT, the Moon will be at its furthest
point from the Earth in 2017, a distance of 406 604 km. The Moon orbits
the Earth every 27.5 days, and like most orbiting bodies, its orbit is
not completely circular, but slightly elliptical, so that the distance
between the two bodies varies by about 3% over the course of a month.
This elliptical orbit is also not completely regular, it periodically
elongates then returns to normal, making some perigees closer than
others. Because this is an elongating and contracting elliptical orbit,
rather than a change in the average distance between the Earth and the
Moon, the most extreme Lunar Perigee and Apogee of each year typically
happen in the same Lunar Month; though this year the closest Lunar Perigee occurred 26 May at 1.24 am GMT, with the second closest occurring to weeks ago at 8.43 am on Monday 4 December.
Diagram showing the relationship of the Lunar orbit and Lunar month. Southern Astronomical Delights.
Although this is the furthest point from the Earth that the Moon will
reach in 2017, it is not exceptional. The Moon reached 406 659 km from
the Earth on 31 October 2016, and will reach 406 634 on 16 August 2023.
See also...
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