Comet C/2011 L4 (PANSTARRS) is on its way and may give amateur astronomers around the world the opportunity to study a bright and interesting target. The comet itself has some very interesting properties. According to researchers, PANSTARRS appears to have a compact, asymmetric coma and is actively producing dust. This is very exciting news for observers because this dust production could make for breath-taking structure - of both of the comet itself and the tail. As it passes through the Solar System and nears the Sun, it may reach a maximum magnitude of -1 and be capable of being seen at a dark sky location as a +1 magnitude comet with a 10° to 20° long tail!
Right now, the question on everyone's mind is the location of Comet C/2011 L4 and its appearance. As of January 2013 PANSTARRS is a Southern Hemisphere object and should be gaining about a tenth of a magnitude of brightness on an almost daily basis. By January 19th, it will have reached the Scorpius / Corona Australis region (RA 18 15 15.0 Dec -43 06 27) and should be dancing in the skies at magnitude 8! This puts the comet well within reach of average backyard telescopes (4.5" to 6") and able to be picked up by larger binoculars at dark sky locations.
By Februrary 5 Comet PANSTARRS will have tracked to its most southerly declination (RA 19 47 51.9 Dec -45 37 32). After it reaches this area of the sky, it will begin its journey northward. According to predictions, it should be brightening fast - at a rate of between one and two-tenths of a magnitude per night. On Februrary 15, 2013 - if all goes as surmised - Comet PANSTARRS should have reached an unaided eye magnitude of 4.6 and be located in the vicinity of Microscopium (RA 21 11 14.3 Dec -43 40 56). Just remember that it will still be a Southern Hemisphere object at this time, so it would only be visible from locations in the Southern Hemisphere, and sky conditions will play a great role on whether or not it can be seen without optical aid.
As Comet PANSTARRS heads toward the Sun, it will continue to become more and more visible. By March 1, 2013 it should have achieved a bright magnitude of 1.9 and located in Pisces (RA 23 25 18.0 Dec -27 18 25). Comet C/2011 L4 will pass closest to Earth on March 5. No need to worry about a potential impact, though? it will still be about 1.10 AU from our home planet during its closest approach - just a little more distance than the Earth is from the Sun. At this point, it should reach magnitude 1 and still be located in the constellation of Pisces (RA 23 55 55.4 Dec -18 27 08). According to JPL/HORIZON predications the comet could be brightest between the dates of March 8-12, reaching a blazing magnitude near -0.5. However, it is still on the move and PANSTARRS will be closest to the Sun (perihelion) on March 10, 2013 at a distance of 0.30 AU.
March is the time for Northern Hemisphere observers to begin to get excited! If you live at very low latitudes, chances are that Comet PANSTARRS should be visible at your location - just 15° from the Sun - around the magic date of March 15th. If the comet's trends follow predictions, it will have probably dimmed to magnitude 1 by that time and be an incredible vision low on the sunset horizon and located in the constellation of Pisces (RA 00 33 07.8 Dec +07 10 29).
Mid-March is time for Comet C/2011 L4 PANSTARRS to begin its sojourn northward. Less than a week after its close approach to the Sun - around the date of March 20th - it should dim by a full magnitude as it reaches the border of Pisces / Andromeda (RA 00 35 20.4 Dec +17 50 42). However, there's still good news for observers! At an estimated magnitude 2, the comet will still be an easy unaided eye object from a dark sky location and glorious in any set of optics!
As Comet PANSTARRS moves further away from the Sun, it will begin losing a tenth to two-tenths of a magnitude per night. By April 1, 2013, it will have faded to magnitude 4.4 and be located in Andromeda (RA 00 31 16.6 Dec +36 33 27). A month later, on May 1, it will have returned to a much dimmer magnitude 7.5 and be located in the Cassiopeia / Cepheus region (RA 00 11 17.9 Dec +67 12 23). This means it should still be within reach of larger binoculars (with 50mm or larger objective lenses) from a dark sky location and well within the range of medium-sized telescopes (4.5"-6"). By May 28, 2013, it will have reached its most northerly declination (RA 19 28 57.2 Dec +85 13 44 and should be around magnitude 9.3.
Does this news mean you'll no longer be able to follow Comet PANSTARRS? Not necessarily. While Comet C/2011 L4 will continue to loose around one to two tenths of a magnitude in brightness per night, it will become circumpolar and be able to be viewed by most Northern Hemisphere observers at any time during the night. On June 1, 2013, it should be located in the Ursa Minor / Draco region (RA 17 20 23.9 Dec +84 31 17) and be at an estimated magnitude 9.5. If you have a larger telescope (12" and up), you should be able to continue to observe Come PANSTARRS for at least another two months. It will remain in the Ursa Minor / Draco region through July 1 (RA 31 13.3 Dec +66 57 34) at magnitude 11 and then continues on through August 1 towards the constellation Bootes (RA 14 40 55.2 Dec +51 29 45) at a very faded magnitude 12.
As always, each comet is unique, and predictions are just that - predictions. Comet PANSTARRS could perform exactly as the professional astronomers think it might, or it might become a surprise. Remember that all brightness and tail estimations rely upon how much the comet dissipates as it nears the Sun and viewing depends greatly on sky conditions at your location.