The moon’s distance from Earth varies throughout its monthly orbit because the moon’s orbit isn’t perfectly circular. Every month, the moon’s eccentric orbit carries it to apogee – its most distant point from Earth – and then to perigee – the moon’s closest point to Earth – roughly two weeks later.
In this post, beneath the illustration below, we list the year’s 13 perigees and 13 apogees. Yes, the moon’s apparent size in our sky does change across this cycle of the moon. The variation in the moon’s apparent size – across its monthly orbit – is akin to that of a U.S. quarter versus a U.S. nickel.
Also in this post, we share with you a little-known fact about the intriguing cycle of close and far moons.
This year’s closest perigee comes on May 26, 2017 (221,958 miles or 357,207 km) and the farthest apogee happens on December 19, 2017 (252,651 miles or 406,603 km). That’s a difference of about 30,000 miles (50,000 km). Meanwhile, the moon’s mean distance (semi-major axis) from Earth is 238,855 miles (384,400 km).
Lunar perigees and apogees in 2017
Perigee | Apogee | |
January 10 | January 22 | |
February 6 | February 18 | |
March 3 | March 18 | |
March 30 | April 15 | |
April 27 | May 12 | |
May 26 | June 8 | |
June 23 | July 6 | |
July 21 | August 2 | |
August 18 | August 30 | |
September 13 | September 27 | |
October 9 | October 25 | |
November 6 | November 21 | |
December 4 | December 19 |
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Amazingly, in periods of four years, lunar apogees and perigees fall on the same, or nearly the same calendar dates. Let’s look four years ahead, to the year 2021:
Lunar perigees and apogees in 2021
Perigee | Apogee | |
January 9 | January 21 | |
February 3 | February 18 | |
March 2 | March 18 | |
March 30 | April 14 | |
April 27 | May 11 | |
May 26 | June 8 | |
June 23 | July 5 | |
July 21 | August 2 | |
August 17 | August 30 | |
September 11 | September 26 | |
October 8 | October 24 | |
November 5 | November 21 | |
December 4 | December 18 |
Also, in cycles of two years, the calendar dates remain the same, or nearly so, except that the lunar apogees and perigees trade places. For instance, let’s look two years beyond 2017, to the year 2019:
Lunar apogees and perigees in 2019
Apogee | Perigee | |
January 9 | January 21 | |
February 5 | February 19 | |
March 4 | March 19 | |
April 1 | April 16 | |
April 28 | May 13 | |
May 26 | June 7 | |
June 23 | July 5 | |
July 20 | August 2 | |
August 17 | August 30 | |
September 13 | September 28 | |
October 10 | October 26 | |
November 7 | November 23 | |
December 5 | December 18 |
Want to know more? Here’s for a complete listing of all lunar perigees and apogees for the 21st century (2001 to 2100).
Here’s a little-known fact of the moon’s apogee/perigee cycle, among both professional astronomers and lay people. That is, the cycle causes lunar apogees and perigees to align on the same, or nearly the same, calendar dates every four years. That’s because 53 returns to perigee (or apogee) are nearly commensurate with four calendar years.
The mean length of the anomalistic month (perigee to perigee, or apogee to apogee) is 27.55455 days, whereas the average Gregorian year equals 365.2425 days. Hence:
27.55455 x 53 = 1460.3912 days
365.2425 x 4 = 1460.97 days
Bottom line: In periods of four years, lunar apogees and perigees fall on the same, or nearly the same calendar dates.