Looking Up – Bob Eklund

ECLIPSE OF THE SUN THIS SUNDAY, MAY 20th – People with clear skies across most of North America will experience a partial eclipse of the Sun late this Sunday afternoon (May 20, 2012). Only those near the Eastern Seaboard will miss out on this awesome cosmic event.

If you happen to be in a swath of land running from Northern California to Texas, you’ll get a very special kind of partial eclipse: an annular eclipse, in which the rim of the Sun becomes a brilliant ring completely encircling the black silhouette of the Moon.

For Los Angeles area viewers, the Sun will be moving down the afternoon sky when a dark dent begins to intrude into one edge at 5:24 p.m. The dent is the silhouette of the new Moon traveling along its monthly orbit around the Earth. The dent will deepen, eventually turning the Sun into a thin crescent. Maximum eclipse will occur at 6:38 p.m., with the Moon covering 79% of the Sun’s area. The eclipse will end at 7:42 p.m., 10 minutes before sunset.

The eclipse will become annular (a “ring eclipse”) for parts of southern Oregon, northern California, Nevada, Utah, Arizona, New Mexico, and a bit of Texas. The annular aspect makes this the first “central” solar eclipse (meaning total or annular) to cross the United States since 1994. Untold numbers of people are planning to travel to the path of annularity for the grand event.

Americans are seeing the tail end of this eclipse. Its annular part begins at sunrise along the southern coast of China (where the local date is May 21st), then crosses parts of Japan, including Tokyo on the centerline. It then speeds across the North Pacific through much of the day before making landfall on the California-Oregon coast in the late afternoon of the 20th (local date).

“Annular” means “ring-like.” This is the kind of eclipse we see when the Moon is at its farthest from Earth, at which time it appears slightly smaller in the sky than the Sun does. The Moon will be practically at the apogee of its orbit—just two weeks, or half an orbit, after it was a “supermoon” (at perigee, or closest approach) when full on May 5th.

Only 88% of the Sun’s surface area will be blocked during annularity. “This will cause less change in the daylight than you might think,” says Alan MacRobert, a senior editor of Sky & Telescope magazine. “Moderately thin clouds would dim the sunlight more. And if you’re where the eclipse is only partial, the dimming will be less.”


The exposed part of the Sun will remain blindingly bright—literally so—and anyone viewing any part of this eclipse, partial or annular, must use a safe solar filter, such as a #13 or #14 rectangular arc-welder’s glass or an astronomer’s filter made specifically for Sun viewing. Ordinary dark glasses won’t do. Watching the Sun through an inadequate filter (or none) can permanently damage your eyesight.

Sky & Telescope’s website describes several recommended Sun-viewing methods:

Other things to look for during this eclipse include a silvery or metallic quality to the light around the time of annularity or when the Sun is a thin crescent. Look for images of the crescent or ring Sun being cast under leafy trees; small openings between leaves make natural “pinhole cameras” that project images of the Sun on the ground.


Another sky spectacle is coming up soon. Just 16 days after the eclipse, on the afternoon of June 5th, it’s the planet Venus’s turn to cross the face of the Sun. The silhouette of Venus will be a small black dot with just 3% the diameter of the Sun, compared to the Moon’s 94% on May 20th. Read all about the transit of Venus on Sky & Telescope’s website:Eclipse graphics:

For an image of how the eclipse will look from Los Angeles:


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