A Supermoon is a Full Moon which appears larger than usual in our skies. The Moon’s orbit is not perfectly circular, but is elliptical. This means that there is a point in its orbit that is closer to Earth than any other (called ‘Perigee’) and a point that is further (‘Apogee’). The orbit takes 27.3 days, so the Moon is at Perigee exactly once every 27.3 days. However, the cycle of phases takes a little longer (Because they are connected to the position of the Sun, and the Earth moves quite far in a month) at 29.5 days. So a little more than once a year, Perigee happens at the same time as Full Moon, and you get a Supermoon. Unfortunately, the actual size difference is small enough that you would never notice unless you already knew to look for it. In fact, the optical illusion which makes the Moon look larger when it’s near the horizon than when it’s high in the sky actually has a much greater effect on the size than the actual measurable difference caused by a Supermoon.
Written by Allen Versfeld
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