For the next few weeks early-morning commuters throughout the Pacific Northwest will be given a preview of Comet Hale-Bopp. The comet is now brightening steadily and is visible to the naked eye in the eastern pre-dawn sky.
The comet, named for astronomers Alan Hale and Tom Bopp who discovered it in 1995, is an ancient, dusty ice ball, probably no more than five to 10 miles across. It is returning to the inner solar system on an orbital cycle that takes about 3,000 years to complete. UW astronomy lecturer Joanne Hughes notes that as the comet approaches the sun on its long, cigar-shaped orbit, solar heat causes it to release a spray of molecules and dust particles that reflect the sunlight. These particles stream behind the comet, forming a very bright, clearly visible tail.
Earthly watchers will see the comet continue to brighten and then grow a longer tail over the next eight weeks, says Hughes.
The comet, which is roaring into the inner solar system at about 40,000 miles an hour, will be 120 million miles from the Earth at its closest point. That is further than the distance of the sun from the Earth. It will come no closer to the sun than 85 million miles, “not especially close as these things go,” says Hughes.
As viewed from Washington and Oregon over the next few weeks, says Hughes, the comet’s daily path across the sky will be to the northeast. It can now be seen at about 6 a.m. about 25 degrees above the eastern horizon (easily measured by holding up two fists on the horizon). Says Hughes: “Look for a bright star in the eastern sky. That is Altair. Then scan upwards and to the left. The comet, its brightness dimmed by the bright sky around the metropolitan area, will appear as a faint, fuzzy object.”
By mid-March, Hale-Bopp will brighten and sink slowly to the northeastern sky, where it will be seen lower above the horizon. By then it will also be visible in the evening, about an hour after sunset, in the northwest sky about 20 degrees above the horizon.
For best views of the comet, says Hughes, find an area surrounded by a dark expanse, such as the Puget Sound or the mountains. Because the comet is still quite faint, intense concentration is needed to find it in the sky. Don’t, she warns, try to find the comet while driving. Apart from the danger from lack of concentration, oncoming headlights compromise the eye’s ability to respond to faint, low-contrast objects.
The UW astronomy department will announce opportunities for public viewing of the comet, tentatively scheduled between March 26 and 29.
Joanne Hughes is at 685-2155, or at firstname.lastname@example.org
Also, check the UW astronomy department’s web page at http://www.astro.washington.edu
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