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Close and far moons in 2016

This year’s 14 lunar apogees (far moons) and 13 lunar perigees (near moons). We also share a secret with you on the intriguing cycle of far and close moons.

Full moons at apogee (left) and perigee (right) in 2011.  Composite image by EarthSky community member C.B. Devgun in India.  Thanks, C.B.!

Full moons at apogee (left) and perigee (right) in 2011. Nowadays, a full moon at perigee is often called a supermoon. Composite image by EarthSky community member C.B. Devgun in India. Thanks, C.B.!

Although the moon’s mean distance (semi-major axis) from Earth is 384,400 kilometers (238,855 miles), the moon’s actual distance varies throughout the month because the moon’s orbit is not perfectly circular. Every month, the moon’s eccentric orbit carries the moon to apogee – its most distant point from Earth – and then to perigee – the moon’s closest point to Earth – roughly two weeks later.

We list the year’s 14 apogees and 13 perigees beneath the illustration below. This year’s farthest apogee happens on October 31, 2016 (406,662 kilometers or 252,688 miles), and the closest perigee comes on November 14, 2016 (356,509 kilometers or 221,524 miles). That’s a difference of over 50,000 kilometers or 30,000 miles. The variation in the moon’s apparent size in our sky is akin to that of a US quarter versus a US nickel.

Also, we share a little secret with you on intriguing cycle of far and close moons.

The moon's orbit around Earth is not a perfect circle.  But it is very nearly circular, as the above diagram shows.  Diagram by Brian Koberlein.

The moon’s orbit around Earth is not a perfect circle. But it is very nearly circular, as the above diagram shows. Diagram by Brian Koberlein.

Lunar apogees and perigees in 2016

Apogee Perigee
January 2 January 15
January 30 February 11
February 27 March 10
March 25 April 7
April 21 May 6
May 18 June 3
June 15 July 1
July 13 July 27
August 10 August 22
September 6 September 18
October 4 October 16
October 31 November 14
November 27 December 12
December 25 January 10, 2017

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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 2020:

Lunar apogees and perigees in 2020

Apogee Perigee
January 2 January 15
January 29 February 11
February 26 March 10
March 24 April 7
April 20 May 6
May 18 June 3
June 15 July 1
July 12 July 27
August 9 August 22
September 6 September 18
October 3 October 16
October 30 November 14
November 27 December 12
December 24 January 9, 2021

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 2016, to the year 2018:

Lunar apogees and perigees in 2018

Apogee Perigee
January 15 January 1
February 11 January 30
March 11 February 27
March 26 March 26
May 6 April 20
June 2 May 17
June 30 June 14
July 27 July 13
August 23 August 10
September 20 September 8
October 17 October 5
November 14 October 31
December 12 November 26
January 9, 2019 December 24

Want to know more? Click here for a complete listing of all lunar perigees and apogees for the 21st century (2001 to 2100).

It’s hard to believe that this rather straight-forward four-year apogee/perigee cycle is so little known among professional astronomers and lay people alike. Lunar apogees and lunar perigees align on the same, or nearly the same calendar dates every four years, 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

View larger. | Image via Wikipedia.

View larger. | Image via Wikipedia.

Close and far moons in 2015

Bottom line: In periods of four years, lunar apogees and perigees fall on the same, or nearly the same calendar dates.

Bruce McClure

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