UW News

March 19, 1997

A partial lunar eclipse and a brilliant Comet Hale-Bopp could provide a celestial light show for Palm Sunday

Palm Sunday this year will be notable not only for its symbolism as the solemn opening to holy week. It will also be the day on which Earth, moon and Comet Hale-Bopp combine to provide what promises to be a celestial light show.

If clouds don’t intervene over the Northwest, there will be a grandstand view of what University of Washington astronomer Donald Brownlee believes will be “one of the brightest comets of our time.”

The curtain will rise with a partial lunar eclipse. At 6:20 p.m. on Sunday, the pale fringe of the Earth’s shadow, called the penumbra, will be visible. Then, at 7, the Earth’s shadow will begin moving across the disk of the full moon. And by 8:40, a maximum of 92 percent of the lunar disk will be covered by the dark, sharp-edged umbra of the Earth’s shadow. The moon, says UW astronomy lecturer Joanne Hughes, will appear darkened and reddened, with a bright, white cap.

The partial eclipse will end at 10:20 p.m., and the penumbra will disappear 40 minutes later.

The effect, says Hughes, should be even more dramatic than during the total lunar eclipse last September, when Saturn hovered just above the darkened moon. This Sunday, it will be Mars, a much brighter, orange planet, that will be seen above or to the right of the moon.

Act two of the drama should be the view of Comet Hale-Bopp to the northwest, about 20 degrees above the horizon (easily located by holding up two fists on the horizon).

Because the “light pollution” from the full moon will be switched off by the partial eclipse, says Hughes, “it will be an ideal time for viewing the comet.” Adding to the ideal viewing conditions, Hale-Bopp will be approaching its perigee, its closest point to the Earth on its giant elliptical swing around the sun. On Sunday and Monday the comet will be about 120 million miles from the Earth. The comet will remain this brilliant for about two weeks.

Everyone, declares Brownlee, “should take advantage of this comet because it may be a century before we get a comet this bright again.” Comet-watchers are seeing an intensely white object with two tails streaked against the sky, one blue, consisting of gas, the other a yellowish-white tail of dust. It is visible, even with the naked eye, an hour before dawn, in the northeast sky, and an hour or so after sunset to the northwest. “It is already the most startling thing in the morning sky,” says Brownlee.

How bright is Hale-Bopp? Astronomers use a magnitude scale to rate astronomical objects by their relative brightness to each other. The brighter the object, the lower it is on the magnitude scale. Thus, the sun is -26, the moon -10, and the faintest star that can be seen with the naked eye is 6.5. Hale-Bopp, says Brownlee, has just moved down past zero to negative magnitude, “which makes it somewhat brighter than predicted.”

It is as bright, and probably will be brighter, than three other major comets of the past three decades: Ikeya-Seki in 1965, Bennett in 1970 and West in 1976. Although it is a good deal brighter than last year’s Comet Hyakutake, its tail is about six times smaller: about 120 million miles long.

Brownlee has just one regret: that Hale-Bopp didn’t come this close some three months ago when both the comet and the Earth were at their nearest point to the sun. “The comet would have been awesome, perhaps the comet of the millenium,” he says. Perhaps Hale- Bopp will oblige the next time it comes this way again — in about 3,000 years.

For more information contact:
Brownlee at (206) 543-8575 or brownlee@astro.washington.edu
Hughes at (206) 685-2155 or hughes@astro.washington.edu

Excellent views of Comet Hale-Bopp are on the World Wide Web:
Sky & Telescope —
The European Southern Observatory —
(Check the sites for photo credits.)



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