By John Hacker

Globe Staff Writer

For people who watch the sky, one clearly visible comet in a year is outstanding, and seeing two comets in one year is rare. But sky-watchers will soon have the opportunity to see three comets.

"This is an exciting time to watch the sky, whether you are an amateur or you do this for a living," Dr. Brian Marsden, with the Smithsonian Astrophysical Observatory in Cambridge, Mass., said in a telephone interview.

Two comets are in the sky now, Marsden said, but people interested in seeing them should bring their binoculars and set their alarm clocks early.

Comets Bradfield and Linear are morning objects for now, rising just before the sun, Marsden said. Bradfield, which was discovered in March, is moving away from the sun and will dim rapidly.

In late May, Linear, which will be visible only from the Southern Hemisphere for most of the month, will rise for an encore in the Northern Hemisphere.

A chance to see a celestial "dirty snowball" will come after the first week of May as the comet NEAT moves into view in the evening sky, moving higher and higher as it moves away from the sun.

Dr. David Kuehn, professor of physics at Pittsburg (Kan.) State University, said he's been keeping track of the comets and is planning programs for the public at the observatory at the Greenbush Education Service Center, west of Girard on Kansas Highway 57.

Kuehn said the programs are scheduled for 8:30 p.m. May 15 and May 21, and will focus on NEAT.

Marsden said Bradfield will probably be beyond the view of the backyard observer by early May, but Linear and NEAT could provide an impressive show for the next two months. They could also fizzle out, as some other comets have done in recent years.

"It's awfully hard to predict the brightness of these comets, especially Linear," he said. "As far as we know, both are coming close to the sun for the first time, and we have no historical observations to compare them to."

Marsden said people looking for Bradfield and Linear in the last week of April should get out their binoculars and find a clear view of the eastern horizon before dawn.

Bradfield will be visible on the northeastern horizon, and Linear will show to the south or east just before sunrise.

Bradfield will fade into the distance and Linear will drop below the southern horizon in the first week of May, but viewers can shift their attention to the evening sky just after sundown for NEAT.

Marsden said NEAT will hit its stride by the week of May 9, coming up in the southwestern sky in the evening and rapidly getting brighter.

Between May 12 and 16, NEAT will line up with the four bright planets - Venus, Mars, Jupiter and Saturn - to provide a dramatic lineup.

"Venus will be very bright, then Mars will be dimly lit to the left of Venus," Marsden said. "The comet will be to the left of both of them, in line with the stars in the constellation Gemini."

In late May, Linear will reappear in the west-southwestern sky and will climb higher in June, but it will remain dimmer than NEAT.

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