Partial solar eclipse is on the horizon
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The second partial solar eclipse of 2007 will take place Tuesday, Sept. 11.

On March 19, much of central and western Asia as well as a part of Alaska saw the new moon partially eclipse the sun. Now, just under a half a year later, the moon will again appear to cross in front of the sun.

The dark shadow cone of the moon (known as the umbra), from where the grand spectacle of a total eclipse is visible, will completely miss the Earth, passing 499 miles (802 km.) below the South Pole and out into space.

Meanwhile, the moon's outer shadow (known as the penumbra), from where the moon will appear to partially eclipse the sun, will slice into a part of Antarctica and the lower two-thirds of the South American continent giving a potential viewing audience of over a quarter of a billion people the opportunity to watch the moon partially cover the sun.

The spectacle of a partial solar eclipse is usually shunned by professional astronomers because it lacks the drama and beauty of a total solar eclipse. Yet, a partial eclipse of the sun affords many people the opportunity of viewing firsthand the dark disk of the moon crossing in front of the sun.

Philip Harrington, in his book, "Eclipse!" (John Wiley & Sons, Inc., 1997), writes: "A partial eclipse, whether or not it leads to totality or annularity, offers a wonderful opportunity to experience the magic of astronomy."

The penumbra first touches down over Bolivia at 10:26 UT (Universal Time), not too far to the east of the capital city of La Paz. The shadow quickly spreads eastward and by 11:30 UT virtually all regions in South America that are within the visibility zone of this eclipse are under the shadow.

Just over an hour later, at 12:31 UT, greatest eclipse occurs over open ocean waters, to the west of the Drake Passage (which has earned a place in history as having some of the roughest sea weather on the planet). A shipboard observer would see the sun sitting on the sea horizon, a bit to the north of due east and resembling a slice of cantaloupe; a fat orange-yellow crescent with the cusps pointing straight up. The partial eclipse peaks at this spot on the Earth with 74.9-percent of the sun's diameter covered by the moon's dark silhouette.

The shadow then turns south where the closing stages of the eclipse may be seen from a few remote research stations in Antarctica, where the sun takes 9 or 10 hours just to skim above the local horizon, moving east-northeast to west-northwest, while peaking very low in the north. The penumbra finally leaves the Earth at 14:37 UT.

One word of caution to those who will be in the eclipse viewing zone – be very, very careful about the precautions for eclipse viewing. Neverlook at even a tiny bit of the sun's disc unless you are using a proper filtration device like No. 14 welder's glass or aluminized Mylar plastic to protect your eyes! The safest method is not to look at the sun at all, but rather project its image through a pinhole and onto a piece of white paper or cardboard. More safe viewing tips can be found here.

Times for locations in South America and Antarctica can be accessed from the NASA Eclipse Home Page.

Coming attractions
Next year there will be two solar eclipses. Both are central, the first being an annular on Feb. 7 that few are likely to see as it passes across Antarctica. On Aug. 1, the first total solar eclipse in nearly two and a half years will start over the Northwest Passage of Canada, gives a glancing blow to northern Greenland, then heads southeast through Siberia and western Mongolia before ending near the famed Silk Route of China.

(Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.)