Friday, June 25, 2010

June 24, 2010: This Saturday morning, June 26th, there's going to be a lunar eclipse—and for many residents of the USA, it's going to be a big one.

The eclipse begins at 3:17 am PDT (10:17 UT) when the Moon enters the sunset-colored shadow of Earth. By 4:38 am PDT (11:38 UT), the moment of greatest eclipse, 54% of the Moon's diameter will be covered. From beginning to end, the event lasts almost three hours.

Although the eclipse is only partial, it will be magnified in size and charm by the "Moon Illusion"--a result of the eclipse occurring close to the horizon from viewing sites in the USA.

For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects. In fact, a low Moon is no wider than any other Moon—cameras prove it—but the human brain insists otherwise.

Who are we to argue?

The effect will be particularly strong in western and central parts of the USA and Canada where the Moon will be setting as the eclipse reaches maximum. (Observing tip: Look low and to the west just before dawn.) The fact that the extra size is just an illusion in no way detracts from the beauty.

People in New England and northeastern Canada will just miss it. The Moon sets shortly before the eclipse begins.

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