Viewing and Imaging Comet ISON - First Sight & Early Predictions
Boom or bust? Comet of the Century or interesting astronomical footnote? Comet ISON, like all long-period comets, is extremely unpredictable. No one knows how the different mixtures of water ice, exotic ices like methane, and dust will react to the growing heat of the sun. Predictions by NASA and other experts right now still look quite favorable with a brightness around that of the planet Venus at peak in late November, though the chance of Comet ISON becoming “as bright as the full moon” are becoming more remote.
Most stargazers and astroimagers are primarily interested in seeing what the comet does after perihelion as it rounds the sun and begins to rise in the evening sky in December. Will Comet ISON survive its plunge into the solar corona, or will the heat cause it to fragment into pieces? Even if it breaks apart, can we still hope for a spectacular tail like Comet Lovejoy showed in the southern hemisphere in late 2011 after fragmenting or will this be a comet only visible to those who catch it early with a telescope and/or camera? Regardless of what happens, it's exciting to know that from both an amateur and professional standpoint Comet ISON will be the most studied comet since Hale-Bopp. ISON may actually surpass Comet Hale-Bopp in terms of the volume of scientific papers and astro-images if it puts on a show between November 28th and late December.
You don't have to wait until then to see this comet, though! Comet ISON is just beginning to exit the glare of the Sun, as seen from Earth, and it will begin rising farther into the morning sky each day for the next couple months. After that, it will swing rapidly back towards the sun, to hopefully emerge with a long streaming tail in the late autumn sky. Until October, you will need a large telescope (10-12 inches or larger), low eastern horizon, dark sky, and a willingness to get up early to see Comet ISON. An astronomical CCD camera will be a big help to find ISON, by allowing you to see fainter objects than your eyes can see through an eyepiece.
When we get into October and early November, if all goes as predicted, it should be possible to see Comet ISON through a small telescope in the 4-8 inch range. Larger telescopes may be able to show the beginnings of a tail on ISON. It will still be a pre-dawn observing target at this time, so you will need to get up early to find the comet in the morning twilight. By the second half November, Comet ISON may become naked eye visible, though it will be harder and harder to spot as it races toward perihelion – its closest approach to the Sun – on Thanksgiving Day, November 28th .
After that, predictions get a lot spottier, due to the unpredictable nature of comets. As famed comet hunter David Levy said, "Comets are like cats; they have tails, and they do precisely what they want." Astronomers are hoping that Comet ISON survives its dive into the solar corona and begins its return trek toward the outer solar system without breaking into fragments. If so, once it rounds the sun, ISON should be visible in both the morning and evening sky. Though, the morning sky will have a more favorable viewing angle until mid-December. If Comet ISON throws off a long, shimmering tail, it will reach its most visible extent at this time, and should put on quite a show right before dawn or in early evening.
Mid-December should be the time to break out the camera tracking mount and a DSLR with a fast, wide-angle lens to take in the comet against a backdrop of stars; but don't discount the ability of a larger telescope and CCD camera for spotting finer detail in ISON's coma! If ISON survives but is fainter, a medium sized telescope and camera will be the best way of capturing it. The moon will limit visibility somewhat, between December 14 and the 22nd or 23rd, but we will have another good chance to view ISON after that. As the comet moves northward and hopefully stays visible all night long the last week of December and into January, the moon will not be such a distraction.
Regardless of how bright Comet ISON gets as it rounds the sun, or how visible ISON's tail becomes in the weeks following, it will offer a great chance to study a major astronomical event that is already seeing worldwide interest. Even if Comet ISON misses the mark and is fainter than initially or currently predicted, it will result in interesting images – as proven by the recent pass of Comet PANSTARRS this last March.
There are always comets being discovered, all the time. So even after ISON has come and gone, the astronomy gear you’ve used to view or photograph it can see a lot more use. As future comets plunge toward the inner solar system in coming years, you will be ready! Clear skies, and happy comet hunting!