The Edge of an Eclipse for Alaska
Fingers will be crossed all over North and Central America on the morning of May 10, 1994, as skygazing people hope that Tuesday dawns as a cloudless sky. If the day is clear, most Alaskans will be able to see the morning sun with a narrow arc missing from its lower rim. Far to the south of us, observers residing in a band reaching from northern Mexico to Maine may have a chance to see a rare spectacle: an annular solar eclipse.
According to the May issue of Sky & Telescope magazine, which devotes several pages to the impending eclipse, the moon will be near apogee, the point in its orbit when it is at its greatest distance from the earth. The distant moon will appear to be smaller than it usually does, and so it will not entirely cover the face of the sun at totality. The moon's apparent diameter will be only 94 percent of the sun's apparent diameter. Thus, observers who have clear skies at the right time in the right place---for example El Paso, Texas, or Buffalo, New York---will see a brilliant ring of solar fire outlining the moon's dark silhouette.
Alan MacRobert, who wrote the eclipse article in Sky & Telescope, came up with a vivid metaphor to illustrate the size of the bright ring of sunshine. He said the solar ring will average 1 arc minute wide, which is as thin as a basketball hoop with a half-inch rim seen face on from 160 feet away. This skinny ring will nevertheless provide so much light that the overall illumination will be about the same as on a bright but overcast day.
The spectacle will last five or six minutes for people lucky enough to be on or near the centerline of the path of totality. Spectators nearer the edge of that path (for example, Kansas City) will see the annular effect more briefly, and the ring will always look lopsided. Observers at the edges will have one advantage, though; they'll get a longer look at the phenomenon known as Baily's Beads. The mountains and valleys of the moon give our satellite an uneven profile. When the silhouettes of the peaks touch the edge of the sun at the beginning and end of an annular eclipse, the bright solar rim breaks into a string of bead-like points of light. Probably some skilled photographer will record this for those of us not fortunate enough to be at the right place.
For Alaskans, the partial eclipse we can see---weather permitting---will fall at about the time most of us should be at work. In Anchorage, the shadow of the moon will first nibble at the sun at 7:59 in the morning, Alaska Daylight Time; the eclipse will reach its greatest extent at 8:37, and will be over by 9:16. In Fairbanks, first contact will occur at 8:08 ADT, maximum will be at 8:44, and last contact will be at 9:22. In Juneau, the eclipse will begin at 7:45, achieve its greatest extent at 8:36, and conclude by 9:30.
Incidentally, one of the best (and safest) ways to observe a partial eclipse is by using a home-made pinhole camera. Take an index card or other sturdy bit of paper and poke a small hole in it with a sharpened pencil. Hold a second card or stiff piece of plain white paper two or three feet behind the holed card. The hole will project a small, inverted image of the sun's disk onto the other card. The image will undergo all the changes taking place in the sky, but in an easily watched form. If you have made a small hole, the image will be dim but sharply focused; a larger hole makes for a brighter but fuzzier image.
