A bright comet is coming to the skies over Pittsburgh, but cloudy weather or lingering light from the sunset could dim the view of PanSTARRS, which may resemble a plane contrail.
Comet PanSTARRS has been visible from the Southern Hemisphere for the past few months, where it exhibited a comet's signature tail and could be seen with the unaided eye. It initially gained star status shortly after it was discovered in June 2011, showing promise that it would become dazzling.
But earlier this year, its brightness was not meeting expectations.
Observations in late February, though, when PanSTARRS began closing on the sun, showed brightening and indicated it would be visible here, low in the west after sunset toward the middle of March. While optical aid may not be necessary, binoculars likely will help in locating the comet not long after sunset.
Australian amateur astronomer David Lee and his wife, Alison, were able to spot the comet easily early this week after battling a long stretch of cloudy weather at their home observing site near Maitland, New South Wales.
"It was easy [to see] naked eye in the twilight with a short tail visible in binoculars," Mr. Lee told the Pittsburgh Post-Gazette by email. "We were lucky to get it, not only in a clear sky but to see it" at all since it was so close to the horizon. The Lees saw PanSTARRS "in a small gap between trees. We have a very bad western horizon."
If it reaches prominent naked-eye visibility now that it has moved north, it will be a welcome sight for long-starved comet watchers, but it likely won't rival Comet Hale-Bopp of 1997 and Comet Hyakutake of the year before.
Our chance to see PanSTARRS each evening will be limited -- the comet will set, or move below the horizon, less than hour after sunset early in the month and about an hour and 15 minutes by March 20. The sun's fading light may be a glaring problem.
"It's going to be really low and the twilight is going to be so bright," said veteran astronomer Tom Reiland, a Shaler resident who has observed 159 comets since his first, Comet Kohoutek in 1973. "It'll probably have sort of a fan tail to it. In some ways, it'll look like a plane contrail."
On Tuesday evening, PanSTARRS will lie to the south, or left, of the crescent moon, which can serve as a guide in finding the comet. The next night, it will be found to the moon's lower right.
As March progresses, the comet will gain elevation after sunset, but it will lose some of its brilliance as it recedes from the sun. Increasing light from the moon, which will reach its first-quarter phase by March 19, also will hinder observations.
Comet PanSTARRS is named for its discoverer -- the Panoramic Survey Telescope and Rapid Response System, an array of cameras and telescopes that continually scan the sky. The comet was found by a telescope that sits atop the dormant volcano Haleakala on Maui in Hawaii.
The comet will pass within 28 million miles of the sun around 11 p.m. Saturday. It was closest to Earth about 5 a.m. Tuesday, coming within about 102 million miles, so there was no chance of a collision with our world.
Last month's surprise meteor that exploded over Russia and the passing asteroid hours later were small, rocky bodies. But comets are "small, icy objects that originate at the outer edges of our solar system," said John Radzilowicz, senior scientist at Carnegie Science Center. "They are usually composed of a loose collection of ice, rocks and dust. They can range in size from hundreds of feet to tens of miles in diameter.
"When they come close enough to the sun, solar radiation causes them to begin to melt and they develop a thin cloud of gas and particles that surrounds them. This is called a coma. As they get even closer to the sun, solar radiation can push out the gas and dust in the coma to form a long tail behind the comet," he said.
Predicting how bright a comet will appear is difficult.
"We don't know how it's going to react to the sun," said Mr. Reiland, who for more than two decades worked at Allegheny Observatory and is the director of Nicholas E. Wagman Observatory in Deer Lakes Park. The Amateur Astronomers Association of Pittsburgh operates that facility. "There may be too much dust and other dark material ... that may not get burned off enough to leave probably a more reflective surface."
Still, it's worth taking a look, and binoculars will help. An unobstructed western horizon is a must.
"Keep in mind how hard it is to predict the final brightness. We may get a grand show, or just a good one. Part of the fun is waiting to see how it will turn out," Mr. Radzilowicz said.
Many astronomers are hoping 2013 may become the year of the comets. After PanSTARRS departs our skies, attention will turn to incoming Comet ISON, which may become spectacularly bright, and develop a long, blazing tail, in November and December.
For those who want assistance in viewing Comet PanSTARRS, the Amateur Astronomers Association of Pittsburgh (www.3ap.org) will hold observing sessions on clear nights if the comet brightens to expectations. The association operates Nicholas E. Wagman Observatory (724-224-2510) in Deer Lakes Regional Park in Frazer and Mingo Creek Park Observatory (724-348-6150) in Nottingham, Washington County. It's best to call ahead.mobilehome - science
Pete Zapadka: firstname.lastname@example.org, 412-263-1857 or on Twitter @pzapadka. First Published March 8, 2013 5:00 AM