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“Super Moon” photographed by Tim McCord of Entiat, Washington from March 19, 2011 full moon using a camera-equipped telescope.

I am always a bit surprised by the number of posts and mentions on the news each year when the Moon reaches its perigee.  Some people will call last night’s Full Moon the biggest full moon of the year because it coincides with the moon’s perigee — its closest approach to Earth — and so it will appear bigger. That’s why you may have heard a news story about tonight’s SuperMoon. (If you missed it last night or had a cloudy sky, it will be very similar tonight.)

It will still be 221,802 miles (356,955 kilometers) from our planet, but that is closer, so bigger and brighter (if you have a clear night in your area) gets a lot of attention.

The Greek prefix “peri” means close or near. The suffix “gee”, derived from Gaea, means Earth.

It’s nice that the Moon gets some attention and that some people who never look to the night sky will do so tonight.

Perigee is part of the broader family of “apses”, astronomical terms which denote distances of orbiting bodies. Since all orbits are elliptical, each orbit contains both a nearest point and a farthest point. The opposite is the apogee, the farthest or highest point. That event doesn’t get any press at all.

The name SuperMoon was coined by astrologer Richard Nolle in 1979, who defined it as: “a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit (perigee). In short, Earth, Moon and Sun are all in a line, with Moon in its nearest approach to Earth.”  Members of  scientific community prefer the term perigee-syzygy.

Some people claim that in the days before and after a supermoon, the Earth is more subject to natural disasters such as earthquakes and volcanic activity due to the Moon’s increased gravitational force. But most scientists and records indicate that any claim of a supermoon effect is unjustified.

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