Sunday's supermoon will technically be a perigee full moon, the closest full moon of the year, NASA says.

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On Friday, Phobos-Grunt was moving around the Earth at an altitude that varied between 177km (perigee) and 224km (apogee).

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The perigee of its elliptical orbit (the closest point it comes to Earth) has actually risen slightly, and is just above 200km.

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Spielman is coauthor of The Insomnia Answer (Perigee Books, 2006).

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This is known as perigee.

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