Lunar Apogee and Perigee

January 25, 2005


Provided by: Anthony Ayiomamitis
Summary authors & editors: Anthony Ayiomamitis; Jim Foster

The lunar image pair above shows the difference in size between maximum apogee (farthest from Earth) and minimum perigee (closest to the Earth) for 2004. These two photos were taken almost six months apart from near Athens, Greece. Minimum perigee occurred in July, 2004 while maximum apogee occurred in December, 2004. Each photo was taken as the Moon crossed the local meridian. The difference in size of nearly 14% is quite dramatic. In fact, the change in the apparent diameter of the Moon is a monthly phenomenon and is something that can be discerned quite easily during any given lunation by looking very carefully at the full Moon and the waning crescent thirteen days later (or observing a waxing crescent thirteen days earlier).

At apogee, the Moon is approximately 406,500 km away from Earth with an apparent diameter of about 29.5' whereas, at perigee, it's approximately 356,500 km away and is characterized with an apparent diameter of about 33.6'.

The picture of the perigee Moon is more colorful than the apogee photo. This coloration isn't related to distance but rather to the Moon's elevation above the horizon. The Moon is low in the sky in summer and attains a much higher elevation during the Northern Hemisphere winter. Closer proximity to the horizon means greater scattering of moonlight as a result of the greater path-length light must travel (to reach the observer) when near the horizon than when overhead. Take a look at tonight's full Wolf Moon.

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