If predicitions are correct, the year 2013 promises to be a great time to observe comets. While many await the appearance of C/2011 L4 PANSTARRS, a fast and furious apparition is expected from Comet C/2012 S1 ISON. Just where will the comet be located, when can you expect to see it and how may it look? Read on...
As of the beginning of 2013, ISON is visible to both hemispheres and is located in the constellation of Gemini (RA 07 36 37.4 Dec +31 19 15). As February opens it is an extremely dim magnitude 16 - barely a blip on the radar. Flying along in the orbit of Jupiter and slow to change positions (RA 07 17 31.1 Dec +31 43 49), ISON remains lazy to brighten - only gaining about a tenth of a magnitude over a few nights. A month later, at the beginning of March, the comet will have moved just a little bit (RA 06 50 56.1 Dec +31 32 54), yet remains so dim that it will either require an extremely large telescope or the use of astrophotography to observe. However, don't give up hope!
Now we have come to the month of April and Comet ISON has barely changed positions in the sky (RA 06 37 34.9 Dec +30 34 47) and only brightened by about half a magnitude. It will appear as nothing more than a soft, "fuzzy ball" of contrast change. At the beginning of May it is still status quo? very little change in position (RA 06 41 39.2 Dec +29 27 22) and just around a full magnitude brighter than it was three months ago - lost in the glare of daylight. Progression is slow, but it is happening. At the beginning of June it has moved ever so slightly (RA 06 59 17.1 Dec +28 14 14) and it is gaining a tenth of magnitude or so every few days. An exciting comet? Not right now... But things will continue to change.
Summer for the Northern Hemisphere is in full swing by July and Comet C/2012 S1 is still trundling along in the constellation of Gemini, barely changing positions (RA 07 25 Dec 34.2 +26 50 45), yet has gained two magnitudes since the beginning of the year. Observable? Not yet. Just remember it's heading towards the Sun and only telescopes in space will be able to follow it during the daylight hours.
Now let's head into August. Comet ISON will not only begin zipping along the ecliptic plane towards the rising Sun (RA 07 59 59.6 Dec +24 55 42), but it will also be in good company with Jupiter low on the horizon. Things are heating up in more ways than one! ISON will be gaining about a tenth of a magnitude in brightness every other night and September finds it located in the constellation of Cancer (RA 08 41 51.1 Dec +22 07 37) and observable with larger telescopes at magnitude 11.7. By this time it should have a slight coma and perhaps a bright nucleus.
By October, Comet S1 ISON will be spending some quality time with the planet Venus and begin moving its way toward the constellation of Leo (RA 09 34 34.3 Dec +17 37 33). By this time, it will become even more accessible to amateur telescopes at slightly brighter than magnitude 10. The race is on... Each night sees it rapidly gaining in brightness - about two-tenths of a magnitude every 24 hours. It should have a visible coma and a concentrated, sharp nucleus? perhaps even beginning to show a tail!
In November Comet ISON will be scooting along through the constellation of Leo (RA 11 12 22.4 Dec +06 21 55) and within easy reach of binoculars at roughly magnitude 6.4 and heading towards the rising Sun and accompanied by Jupiter, Mars and Venus. This comet is a sun-grazer and the closer it gets to our nearest star, the faster the gases and dust will begin to flow away. How much of a tail will it have by now? How big will the coma be? It's anyone's guess at this point in time, but predictions show it gaining between two and three tenths of a magnitude each night, and changing positions faster. By mid-November it will have rapidly moved towards the morning Sun and can be found buzzing through the constellation of Virgo (RA 12 52 30.3 Dec -06 50 08). If predictions hold true, it should have reached at least magnitude 4 by this time and it is about to begin to blaze! Every 24 hours will see Comet ISON gaining about half a magnitude. Our "traveler" is about to become fantastic!
By November 25th, C/2012 S1 Comet ISON should become an incredible magnitude -0.2 and putting on a breath-taking spectacle in the morning skies scooting along the Virgo / Libra region (RA 15 01 21.7 Dec -20 04 45). But, oh my? It's not even close to finishing yet! The closer it gets to the Sun, the more the tail will grow and the faster it will brighten. Just how fast will these changes occur? While we can't be entirely sure, it is predicted that ISON will jump nine magnitudes in a period of three days - a jump which could possibly make it as bright as the Moon! On November 28th, it might reach an unprecedented magnitude -0.9! In this case, we should thank our lucky stars that it will be that bright to compete with the light of dawn...
From this point forward, Comet ISON will rapidly drop in brightness as its dusty "fuel" becomes exhausted. However, by no means is the show over. The beginning days of December should still find it lighting up the skies at magnitude -0.1 and descending slowly - again just a few tenths of a magnitude every few nights. By Christmas 2013, it should still be an unaided eye object at magnitude 4 and possibly remain as bright as magnitude 4.5 until the end of the year. Will Comet C/2012 S1 ISON become one of the infamous "comets of the century"? Let's face it... We don't know for sure. Each and every comet has unique properties and ISON is no exception. There is just as much possibility it may break apart and fizzle as there is a spectacular performance. What we do know is that there is potential... and that's an exciting word for astronomers everywhere!