Moon Illusion to Supersize Saturday Lunar Eclipse

A partial lunar eclipse set to occur early Saturday should look particularly stunning to observers in parts of North America thanks to an optical illusion that will make the moon look bigger than normal.

The moon will pass through part of Earth's shadow, temporarily becoming dark, starting at 6:17 a.m. EDT (1017 GMT) Saturday morning. That cosmic line-up coincides with the full moon of June and a so-called "moon illusion" that, weather permitting, should offer quite a show, according to a NASA announcement.

For observers in the central and western United States, the lunar eclipse will occur while the moon is still close to the horizon. The partial eclipse begins after the moon has set for observers in the eastern United States. (This graphic shows how the moon will appear during Saturday's three-hour partial lunar eclipse.)?

Even though only 54 percent of the moon's diameter will be covered during the moment of greatest eclipse (around 7:38 a.m. EDT, 1138 GMT), the sight will appear magnified in size and charm by the "moon illusion." [Top 10 lunar eclipse facts]

Scientists aren't completely sure why, but low-hanging moons tend to look exceptionally large. When the moon beams through trees, buildings and other foreground objects close to the horizon, it often appears to be much larger than when it shines from overhead.

Even though cameras prove that low moons are no wider than any other moons, the human brain insists otherwise.

The moon will be most picturesque in the western and central parts of the United States where the moon will be setting as the eclipse reaches maximum. Viewers there should look low and to the west just before dawn to catch the best sight.

The same phenomenon will be visible to observers in India, Japan, and parts of East Asia. The eclipse will occur there on Saturday evening as the moon is rising, with the same illusion in full force. However, in the islands of the South Pacific, the moon will be hanging directly overhead in the midnight sky, so the horizon illusion won't add to the effect.

People in New England and northeastern Canada will just miss being able to see the eclipse.

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