Update: ISON is alive and well!
A Hubble Space Telescope image taken on October 9 is keeping hopes high that ISON will present itself to Earth with an exciting show over the next 2 months.
Taken from inside Mars's orbit, the photo shows an ISON with an intact nucleus with no fragments or clusters. This indicates that the heat-induced breakup that could prevent an impressive lightshow hasn't happened yet.
The ultimate fate of C/2012 S1 will be determined as it continues to plummet towards the sun, but the possibility of a new "Comet of the Century" remains.
Comet ISON is Coming!
Get ready, Earth - the comet of the century is headed your way! Officially named C/2012 S1, but referred to most often as Comet ISON, this ball of ice and dust is prepped to put on possibly the greatest airshow of our time. Or not.
It's a comet from the Oort Cloud, made of ice and dust, about 3 miles across. There's nothing too spectacular about its makeup, but ISON's path is unique. It's a sun-grazer comet, meaning it will come in notably close contact with our sun. ISON will come to perihelion (closest to the sun) on November 28, 2013, swinging by at .012 AU, or 1,100,000 miles. The comet's survival of or destruction during this close passage will determine what we see - it may be so bright as to be visible during the day, or end up invisible to everyone without a good telescope.
NASA and other observational agencies have been tracking ISON since discovery, and will use their full array of devices to gather as much visual information as possible throughout its pass. Starting on Mars - the Mars Reconnaissance Rover and rovers Discovery and Curiosity will take the first close-ups of the comet when it passes by on August 20.
Viewing Comet Ison
In its prime, the right instruments for viewing ISON will be small and medium telescopes with a wide field of view and (we hope) the naked eye. The actual comet is quite small, but the tail will streak across the sky. ISON will have at least one tail - gas or dust. A gas tail is thinner and shines blue and a dust tail is broader and will appear white or yellow.
August and September
ISON is going to be a challenge early in August, gradually become easier to track down as autumn rolls in. Early, it'll be very low over the eastern horizon before the sun comes up - you'll need a good telescope and you won't see much but a small ball of light. Towards the end of August and into September, ISON will be higher, in the constellation Cancer and near Mars and M44. By the middle of September, look for our comet 1/3 of the way up from the eastern horizon before sunrise, 3%deg; left of Mars. By the end of September, we'll have better intel on just how great ISON is going to be.
Comet ISON will continue to get brighter and move across the sky, passing through Leo at the beginning of the month. As ISON passes Mars, we'll get our first good pictures of this curious visitor courtesy of our Martian robots. If things go as we hope, ISON could reach +5 magnitude by this time. As Halloween approaches, it'll be 5° below Mars and begin to head down towards the dawn for its most exciting show yet.
Many are crossing their fingers for naked-eye visibility by this time, but - lucky you - you'll have a telescope. ISON will still be low in the East early in the morning, possibly with a long tail developing. The comet has begun its approach to the sun. As it gets closer, it'll actually disappear into the sun's brightness for about a week. And then … BAM! Perihelion. As ISON shows up on the other side of the sun, it could be as bright as -10 … visible with the naked eye during the day!
After perihelion is when we'll see the sights that get the mystics going … ISONs long tail lingering in the sky. As the comet itself fades rapidly in magnitude, its (hopefully) long tail(s) should remain an impressive nighttime sight for over a week in early December.
*Comet Fact *
Many people think that a comet's tails are drawn out behind it along its path through the sky, like a jet trail. In fact, the dust and gas tail that you see is a result not of motion, but of the sun's energy. The "solar wind" blows particles and gases back with such force that a comet's tail is always facing away from the sun no matter what direction the comet is traveling.