(NEW YORK) — If you live in a band across the southwestern United States, twilight likely seemed to come early Sunday afternoon, well before the sun actually sets. The cause: a rare annular solar eclipse — a ring of sunlight as the new moon, passing between Earth and the sun, blocks most, but not all, of the sun’s disc.
The ring was visible in a strip that began on the California-Oregon coast and stretched southeastward across Reno, Nev., the Grand Canyon, and Albuquerque, N.M., endeding at sunset near Lubbock, Texas.
Denver, Las Vegas, Sacramento, San Francisco, Salt Lake City and Yosemite all saw a partial eclipse — the sun dwindling to a crescent. Even some distant cities, including Buffalo, Chicago and Dallas saw a fair portion of the sun blocked by the passing moon.
Why an annular eclipse instead of a total one? Because the moon, constant in size as it may appear to us, does not move in a perfect circle around Earth. Its orbit is slightly elliptical. On average, it’s about 239,000 miles away, but at its closest it comes within about 225,000 miles of us. At its farthest — as it was Sunday — it’s a little more than 250,000 miles away. It’s just enough of a difference so that the moon will only cover 88 percent of the sun.
(You may recall the “super moon” of two weeks ago; that night the full moon coincided with the low point of the moon’s orbit, making it look a little more vivid than usual.)
The laws of orbital mechanics make solar and lunar eclipses fairly common, actually — just not necessarily visible from where you live. If you were underwhelmed by Sunday’s annular eclipse, there will be a total eclipse on Nov. 13 — but it will only be visible from Australia and the South Pacific.
Copyright 2012 ABC News Radio
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