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.
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.
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 | |
| December 24 | January 9, 2019 |
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) is 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.
Bottom line: In periods of four years, lunar apogees and perigees fall on the same, or nearly the same calendar dates.
from EarthSky http://ift.tt/1TnyMgw
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.
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.
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 |
Enjoying EarthSky so far? Sign up for our free daily newsletter today!
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 | |
| December 24 | January 9, 2019 |
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) is 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.
Bottom line: In periods of four years, lunar apogees and perigees fall on the same, or nearly the same calendar dates.
from EarthSky http://ift.tt/1TnyMgw
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