Keeping track of a bright comet....

After having its every move imaged and analyzed for months, Comet Hale-Bopp has been granted a brief reprieve from the astronomical paparazzi. It has now slipped behind the sun and won't reemerge from the solar glare until February 1996. In the meantime, the comet remains unusually active, raising hopes that it may wow skywatchers when it passes nearest the sun in April 1997.

On Aug. 30, a month after the comet's discovery, Alan Fitzsimmons and Martin Cartwright of Queen's University in Belfast, Northern Ireland, obtained spectra of Hale-Bopp with the 4-meter William Herschel Telescope in the Canary Islands, Spain. The spectra reveal cyanogen in the gases surrounding the icy nucleus of the comet, the astronomers report in the Jan. 13, 1996 Monthly Notices of the Royal Astronomical Society. Ordinarily, researchers see this gas only in comets much nearer the sun than Hale-Bopp, which now lies beyond Jupiter.

From the intensity of the cyanogen emission, Fitzsimmons and Cartwright calculate that the comet vents about 3 kilograms of the gas every second-five times more than Comet Halley released in 1985, when it was much closer to the sun's warming rays. In other respects, however, the comet appears fairly ordinary. It releases carbon monoxide and cyanogen in roughly the same ratio as other comets do, and the dust particles that shroud its nucleus have a typical, slightly reddish tinge. Hale-Bopp, the astronomers conclude, acts like a normal comet-except that it appears much brighter and more active than any other studied at such a great distance.

A report by Michael F. A'Hearn of the University of Maryland in College Park and his colleagues in an Oct. 16 circular of the International Astronomical Union concurs with that conclusion. Analyzing observations by the International Ultraviolet Explorer in late August and early September, the researchers find that Hale-Bopp flings out an enormous amount of dust, perhaps more than any other known comet. Sunlight reflecting off a comet's dusty shroud, or coma, accounts for its brightness. Even if the rate at which the comet spews dust doesn't increase as it nears the sun, "it could still be a monster," says Harold A. Weaver of Applied Research Corp. in Landover, Md.