Comet approaches to light up March skies

Posted Feb. 1, 2013

Even if Comet L4 PANSTARRS doesn’t become the spectacle many of us hope it will be, it will almost certainly be visible with the naked eye and a fine sight in binoculars, with a sweeping tail pointing away from the sun.

The latest predictions by knowledgeable amateur comet observers peg it at between magnitude 2 and 3 when far enough from the glare of the sun to see. That compares well with the brightness of the stars in the Big Dipper. Not too shabby as comets go.

Comet PANSTARRS won’t make its first appearance for northern hemisphere skywatchers until the first week of March during evening twilight. That’s only 5 weeks from now. For the U.S. the comet will appear in the western sky very near the horizon. Observers in the southern states will have a slightly better view with the comet standing a degree or two higher through March 12; after that all locations across the country will be equally blessed. If you want to see it from the start when the comet’s also brightest, you’ll need an observing spot with a view as far down to the western horizon as possible.

Scout your neighborhood or take a drive away from home to a nearby soccer field, park or other place with an open view to the west. Once you’ve found your ideal location, go out on the next clear, moonless night and scan that direction for city light pollution. Unless you live in the countryside, a small amount of city glow is inevitable. That’s OK. Few places are light-pollution free these days.

But if your western sky is filled with a star-swamping, foggy miasma on what is otherwise a dark, clear night, consider putting another 10, 15 or 20 miles between you and your town for a better view. If you need help finding a good site or need additional expertise, contact your local astronomy club. Here’s a directory of clubs across the U.S. (http://bit.ly/YRhKzs).

Because of L4 PANSTARRS’s low altitude during the first half of March, light pollution, natural horizon haze and twilight itself will compromise the view. From first appearance near the sun in the west-southwest around March 7, the comet never gets higher than about 10 degrees (one fist held at arm’s length) between March 8-20, the time during which it’s expected to put on the best show. While the bright head of the comet will still be visible, much of its tail could well be masked by city light or haze. A dark site is best.

Later, as the comet moves northward and higher, it will fade but may become easier to see as it moves into a dark sky. Binoculars should show it through early May and perhaps even later. From mid-May onward, L4 PANSTARRS becomes circumpolar for observers at mid-northern latitudes and remains visible all night long. At that time it will shine around 8th magnitude and require a small to medium-sized telescope to view.

Comet L4 PANSTARRS reaches perihelion (closest to the sun) on March 10 at a distance of 27.9 million miles or about 6 million miles closer to the sun than Mercury is on average. Intense solar heating will cause the comet to grow a fine dust tail that could stretch for many degrees away from the sun. Closest approach to Earth happens on March 5 at 102.3 million miles – hardly a close shave but good enough for a nice show.

As far as the best instrument to use, we’re all hoping PANSTARRS will be bright enough to see plainly with the naked eye. Based on its predicted brightness and tail development, a binoculars will probably provide the best view.

Get a pair that magnify between 7x and 10x with an aperture (lens diameter) of 40 to 60mm. 10×40, 10×50 and 7×50 models are perfect, and they’re reasonably priced, too. Avoid binoculars that magnify 20x or 30x. While more power sounds tempting, anything above 10x will narrow the field of view and make the binoculars nearly impossible to hold steady.

My favorites are the 10×50 wide field variety with lots of eye relief. Large eye relief lets us unfortunates who must wear glasses see the entire field of view instead of getting the equivalent of looking through a straw.

Comet PANSTARRS is what astronomers term a dynamically new object, making its first visit to the inner solar system after millions of years in the deep cold of the comet repository known as the Oort Cloud. Such comets make a bright appearance at great distance because their rarefied ices are ripe to vaporize. This can lead one to think that the comet will continue to brighten into negative magnitudes as it approaches the sun and Earth. But after those virgin ices have sublimed away, new comets often settle down and lag behind predictions. The old hats who’ve been around the block a few times brighten and fade more reliably.

Whatever happens with PANSTARRS is worth watching. As we’ve encountered with previous comets, unpredictability is their charm. The comet could be brighter, fainter, experience a sudden outburst of brightness or disintegrate into clods of dust. I hope we’re all fortunate enough to witness such revelatory moments in nature.

Bob King is the chief photographer at the Duluth News Tribune and an amateur astronomer who blogs at astrobob.areavoices.com

Tags: community, science