Recent observations by European astronomers using the 1-meter telescope at Pic du Midi show that Comet Hale-Bopp (C/1995 O1) rotates every 11.47 hours, but that the spin rate actually varies by about a half hour over a three-week period. This complex rotation, which may include precession, is combining with a prominent jet or jets of dust to create the multiple bright shells that have been observed on the sunward side of the nucleus. The comet will be closest to the Earth this coming weekend (197 million km) and to the Sun on April 1st (137 million km).
Meanwhile, the comet is obvious in both the morning and evening skies from mid-northern latitudes. On March 13th, S&T Contributing Editor John Bortle said that with his unaided eye he traced Hale-Bopp's faint ion tail out to more than 16 degrees, while the brighter dust tail extended 9 degrees. Mornings are probably still the better bet, as this week the waxing Moon will become a problem in the evening. The comet's total magnitude is now about -0.3. To see Comet Hale-Bopp you'll need to look at least 1 1/2 hours before sunrise or after sunset, though its starlike inner coma can still be seen in twilight. It's about 20 degrees above northeastern horizon before dawn, and the roughly same height above the northwestern horizon in the evening.
This week we finally start to see the comet as high in the evening sky as it is before dawn. Just look northwest right after the end of twilight (an hour and a half after sunset), or northeast just before the first light of dawn (an hour and a half before sunrise). Look for the fuzzy "star" with a tail.
The comet will rise higher in the evening sky for another week or so and will shine there at its best in late March and early April.
The farther north you are the better. Skywatchers at the latitudes of the northern United States have a better view than those in the southern U.S. Observers in the Southern Hemisphere miss out entirely (until late April or May).
Light pollution and moonlight will diminish what you can see of the comet, especially the tail. But binoculars will give a grand view under any conditions.
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