June 25, 2010 at 4:28 PM ETIf you live in the Americas, you'll have to get up early on Saturday morning to catch a glimpse of a partial lunar eclipse - but this one should look bigger than you'd expect, thanks to a trick of the eye. This lunar eclipse is actually the second event in this year's eclipse parade, and arguably the least spectacular blackout of the bunch. The really big events are coming up ... including an exotic total solar eclipse next month and a perfectly timed lunar eclipse in the midst of the December holiday season. The heart of Saturday's eclipse won't even be visible from parts of the East Coast. But the fact that it takes place close to sunrise means the eclipsed moon will be low in western skies as seen from the rest of the United States - and that means the well-known "moon illusion" will come into play. The moon always looks bigger when it's near the horizon, as compared with when it's high in the sky. But the reasons for that are still a matter of debate among psychologists: One factor is that the moon's proximity to the horizon leads the viewer to see it alongside tiny distant objects on the horizon. Our primate brains are programmed to perceive the moon as being even farther away, and much bigger than those distant objects. But when the moon is hanging in a big empty sky, our brains don't make that perceptual connection quite as easily. Some researchers say we perceive the heavens as a shallow inverted bowl, with celestial objects high in the sky seeming to loom more closely, like a cloud or a bird directly overhead. Others say the "inverted bowl" theory is dead-wrong, and say the angular-size illusion involves something called oculomotor micropsia. For more perspectives on the moon illusion, check out these archived explanations from NASA Science News, Space.com and Bad Astronomy - and ponder the mystery as you gaze at the morning's darkening moon.
Sky and Telescope This chart shows the progression of Saturday's partial lunar eclipse, with times expressed as UTC (GMT). The peak of the event comes at 11:38 UT, which is 7:38 a.m. ET (after sunrise) or 4:38 a.m. PT.