Yesterday, the Moon was about as small as it could ever get as seen at Full phase. When the Moon reached Full phase yesterday, it was roughly two hours from apogee, the farthest point from Earth in the Moon's orbit. So, what else of this 'Mini Moon?'
According to current scientific theory and shown plausible by computer models, our Moon probably originated in a massive impact between Earth and a Mars-sized body. In the crash, the impacting body was shattered and the outer layers if Earth were thrown into space. For a time, Earth was surrounded by a ring of debris, much like Saturn is today. However, unlike with Saturn, the floating bits of rock and metal reconstituted into a new world, our Moon. In time, thanks to its sheer mass, the Moon would start pulling away from Earth, a process that continues even today at a rate of about an inch a year.
As was first discovered in the early 1600s by Johannes Kepler, all orbiting bodies move in elliptical (slightly elongated) orbits, the Moon is no exception. The fact the lunar orbit is elliptical is the root of the whole 'mini Moon' event that will happen today. Because of the elliptical orbit, the Moon is not always the same distance from Earth, but a varying distance that can change by as much as about 27,000 miles. Tonight, the Moon will come to a point in its orbit that will bring it very close the farthest point in its orbit, a position called apogee.
In practical terms, the fact that the Moon is farther than usual will not amount to much. In a telescope, however, things will be different to an experienced observer. As seen in a telescope, the Moon will be slightly smaller than it is when it is full at perigee (the point in its orbit closest from Earth), especially when put side by side in a composite photograph.
Unfortunately, here in the Cleveland area, the sky was cloudy last night, which means that one must rely on pictures to see the sight for oneself.
As always, would-be sky watchers in the Cleveland area should be sure to keep an eye on the Cleveland weather forecast and, for hour-by-hour cloud predictions, the Cleveland Clear Sky Clock. Live somewhere else? Find a clock and see if it will be clear near you.
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