Like our ancestors, I'm usually filled with dread at the appearance of a new comet; for them it was because they were considered harbingers of doom but for me it's because people look to me (an astronomer) to forecast how bright (or not) they may become.
Therein lies the problem -- comets are notoriously difficult to predict. You only have to look at Comet Kohoutek in 1973, dubbed by many as the "Comet of the Century," which turned out to be a flop. I find myself here again, with Comet C/2011 L4 (PANSTARRS) on the verge of making its Northern Hemisphere debut and people are asking me how it is likely to perform.
One of the reasons the brightness of a comet is hard to predict is that we can never be sure about how much "outgassing" is going to occur. Outgassing is the process where gas, which was previously trapped or frozen in the comet's nucleus, is released into space and, given that the nucleus of a comet is predominantly made of ice, it's not surprising that outgassing can be quite extreme as it nears the sun, heating up.
In fact, it's this process that produces the vast coma surrounding the small icy nucleus. The force from the solar wind pushing against this gas will produce a comet's trademark tail.
Interestingly, the tail of a comet is responsible for their name that comes from the Greek word 'kometes' meaning long-haired star.
Comet Panstarrs, as it is generally known, was discovered back in June 2011 by the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) based at the University of Hawaii's Institute for Astronomy.
Since its discovery, it has been slowly heading toward the inner solar system reaching its closest point to the sun, known as perihelion, on March 10. Since its discovery we've had great hopes for this one becoming a bright "naked eye" comet with early estimates as bright as magnitude -4 which puts it on a parr with Venus. Further observations revealed that its brightness increase was slowing down suggesting less outgassing activity than predicted.
It now looks like its maximum brightness will reach only magnitude 3, a far cry from the brightness of Venus but still visible to the naked eye.
In early February 2013, it was seen for the first time without optical aid from the Southern Hemisphere on its way north. Currently it is sitting in the constellation of Cetus and is heading north east taking it into Pisces and then on March 12, it will pass into Northern Hemisphere skies. It can easily be found on the night of 12th and 13th as it passes close by the crescent moon. By then it will have reached 1st magnitude and be easy to spot -- although, unfortunately, it will be moderately low over to the west at the onset of night.
By the 22nd, it will have moved up into Andromeda where a great photo opportunity exists on April 3 as it scoots close by the Andromeda galaxy -- although by then it will have faded to almost 5th magnitude making it visible only from dark sites.
By the April 13, it will fade from naked eye visibility as it heads up into the constellation of Cassiopeia.
For anyone without a telescope but keen to spot this interplanetary visitor, then the nights of the 12th and 13th really are the best opportunity as the moon will be a great marker to its position.
Look for a faint fuzzy elongated blob of light! Binoculars will reveal its tail in a little more detail and would probably be my instrument of choice to see it in all its glory.
The best view from a telescope will be gained if a low power eyepiece with a wide field of view is used, otherwise higher powers tend to 'zoom' in to close and lots of detail in the tail may be lost.
Bird watching telescopes are actually ideal for comet spotting so even if you don't have an astronomical telescope, its still worth taking a look with one of those. As for other hints and tips to spot Comet Panstarrs, I'm afraid its simply a case of waiting for clear skies and hope it performs as we expect it will.
But, if you miss it, you will have 110,000 years to wait for its next appearance.
Fortunately, an even brighter comet is hot on its heels: Comet ISON. But we'll have to wait until November for that one -- and there is no way you'll get my forecast for that one... not yet, at least.