Tuesday, April 28, 2015

Tonight's Sky for April 28: Moon at Apogee

Tonight, the Moon is about as small as it will ever get thanks to the fact that the Moon is at apogee, a point in its orbit that is farthest from Earth.

What many people may not realize is the fact that the Moon (and all other celestial bodies) do not orbit their parent bodies in circles, but ellipses, which are slightly elongated circles. Result: any given day of an orbital period, any orbiting body will be at a slightly different distance from its parent body. As for the Moon, this variance in orbit amounts to about 20,000 miles.

As for tonight, the Moon will be about as far from Earth as it is going to get. When it comes to practical implications, the difference will be hard to notice with the naked eye to all but an experienced observer but, in a telescope,
the difference will be obvious.

As an afterthought, while two full moons taking place in a single month get a lot of hype even in the non-astronomical media, apogee moons don't, which is a bit of a shame in that April, 2015 offered a pair of apogee moons, with the first taking place on April 1. 

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