Monday, June 28, 2010

In Case You Missed the Eclipse...

Here in Orange County, a layer of coastal fog prevented anyone from seeing Saturday morning's partial lunar eclipse.

But lots of other people throughout the western United States, as well as eastern Asia, the Pacific Islands, and Australia, were treated to the event. One Orange County man, Dave Kodama, headed out to the Orange County Astronomers' private observing site located in the nearby desert, far away from city lights and rarely covered by clouds. There, he got an unobstructed view. He took this spectacular image, showing the Moon setting while still in the Earth's shadow. (If it looks far larger than it ever appears to your eyes, that's an effect of the telephoto lens he was using, which makes distant objects appear much larger than they actually are).

He also made the following video of the eclipse, from just before it began, to when the Moon starts to set (probably about 2 hours). Watch as Earth's shadow descends over the Full Moon:


One aspect of this eclipse that made it unique for observers in western North America was the fact that it occurred when the Moon was approaching the horizon. As anyone who has ever observed a rising or setting Moon knows, the Moon appears larger when near the horizon (a phenomenon known as the "Moon illusion"). It may surprise you to learn that the precise reason for this is still unsettled by scientists. The often cited notion that "you are able to compare it to objects of known size along the horizon", an instance of the optical illusion known as the "Ponzo effect", is considered inadequate by many scientists. But we can be sure it is definitely an optical illusion, and not some kind of magnification: witness the fact that the Moon appears the same size through a given telescope whether at the horizon or at the zenith.

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