Watchers must take precautions to safeguard their eyes if they look at the partial solar eclipse of June 10, reports Prof. Jay M. Pasachoff of Williams College and the Harvard-Smithsonian Center for Astrophysics. The Moon will then go in front of the Sun as seen from Earth, but will not cover it entirely. The eclipse will take place in the late afternoon and until sunset on that date in the United States, Canada, and Mexico. It will be visible in from the whole United States except for the band of the Eastern seaboard that contains the major cities of Boston, New York, Washington, and Miami. From a narrow band across the Pacific Ocean that winds up near Puerta Vallarta, Mexico, at sunset, the moon will be entirely silhouetted against the sun's disk, a situation known as an annular eclipse from the annulus, or ring, of sunlight that will remain. From all these locations, the Moon will gradually cover and uncover the Sun over a period of about two hours. Viewers should not look at the Sun directly, without special filters, whether it is on a normal day or during a partial eclipse.

The eclipse coverage of the Sun by the moon will reach approximately 75% in Los Angeles, 70% in San Francisco, 60% in Dallas, 50% in Seattle, 40% in St. Louis, and 30% in Chicago. It increases in coverage toward the southwest, until 98% is covered beyond Baja California and at Puerta Vallarta. At all times, so much of the everyday Sun will remain visible that it will not grow dark, and the complete darkness and the interesting phenomena of a total solar eclipse will never be visible. The Sun will set during the eclipse from mid-Virginia and mid-New York State westward beyond Kansas City and El Paso.

Unlike a total eclipse, when the Moon entirely covers the Sun and the faint outer layers of the Sun become visible without eye protection, viewers cannot safely look at the Sun at any time during a partial or annular eclipse. The progress of the eclipse is easily viewed with a pinhole camera, which anybody can make by simply punching a small hole, perhaps 1/4-inch across, in a sheet of paper. Pasachoff explains, "Holding that paper up to the Sun over your shoulder projects an image of the eclipsed Sun onto a wall. You view that image while facing away from the Sun, so it is completely safe to look at." The sun will be at a low angle in the sky, so the pinhole image will easily be projected on a wall. Since the eclipse will last two hours, the view changes gradually and there is no need to watch continuously.

Welders glass #14 makes a safe filter through which to view the Sun, and special solar filters are available for purchase, but ordinary dark color film or polarizers are not safe for viewing the Sun. There is no special danger in the rays from the Sun during eclipse, and it is only that people are tempted to look at the Sun during an eclipse more than on an ordinary day that presents any hazard. Now that warnings on how to observe the eclipse safely are widespread, injuries during eclipses are rare.

Partial eclipses like this one provide few scientific opportunities for researchers, unlike total solar eclipses, when otherwise hidden parts of the Sun become visible. The next total solar eclipse will be on December 4, and will be visible only from southern Africa and South Australia. The next total eclipse in the United States won't occur until 2017.

Pasachoff will be in Puerta Vallarta, Mexico, to view his 33rd solar eclipse. He is Chair of the Working Group on Eclipses of the International Astronomical Union, and author of the Peterson Field Guide to the Stars and Planets, which gives information about observing eclipses. See http://www.eclipses.info/.
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Pasachoff can be reached on his cell phone at 617 285 6351, through June 7, and then at the Sheraton Buganvilias Hotel in Puerta Vallarta, Mexico, through June 11.

See http://www.eclipses.info/ for information about this eclipse and about safe eclipse viewing.
See also the map from Fred Espenak of NASA's Goddard Space Flight Center at http://sunearth.gsfc.nasa.gov/eclipse/ASE2002/ASE2002.html.