A new comet was discovered inching across Cancer the Crab in the morning sky may knock your socks off next fall. Based on a preliminary orbit, it could become a very bright object beginning in November 2013 for both northern and southern hemisphere sky watchers. C/2012 S1 (ISON), its formal name, was found by Russian amateurs Vitali Nevski and Artyom Novichonok of the International Scientific Optical Network (ISON), a network of observers who track man-made space debris.
When first photographed on Sept. 21 the comet was an incredibly faint 18.8 magnitude and appeared much like a star with only a “whiff” of a coma around its icy nucleus. It will slowly cruise through the constellation Gemini for many months while growing gradually brighter. And I do mean gradually. Even as late as next June, ISON will only shine at 14th magnitude; that’s scraping the bottom of the bucket for most amateur telescopes.
The situation improves next September when 8-10 inch scopes should pick it up as a small blob in Cancer around 11.5 magnitude. From late October through late-November, things get much cheerier with C/2012 S1 brightening sharply from 7th to 1st magnitude in the eastern sky at dawn. I’m sure I’ll be setting my alarm for a look Thanksgiving morning.
When closest to the sun at perihelion on Nov. 29 it’s predicted to shine a spectacular -7 magnitude or almost 10 times brighter than Venus. Before you say WOW, you need to know the comet will lie only 4.4 degrees north of the sun (very close!) on that date and probably be hidden in the solar glare. Then again, we might spy it in daylight through binoculars by taking proper precautions to keep the sun out of the field of view. Some of us saw the last daylight comet C/2006 P1 McNaught in January 2007 this way.
A second round of excellent visibility commences immediately after perihelion as S1/ISON performs a hairpin turn around the sun and banks north into Ophiuchus and Hercules in early December.
While the comet fades during this time, it’s likely to have a spectacular tail and be as bright as magnitude -4. Both hemispheres will get great views, with the northern favored as Christmas approaches. Indeed, northerners will see it at both dusk and dawn. The comet will pass nearest Earth at a distance of about 37 million miles in January 2014. On the 8th it will appear only 2 degrees from the North Star.
That makes two potentially bright comets in 2013 – the other is C/2011 L4 PANSTARRS. It’s forecast to shine as brightly as Vega next March. While I like what I see, it’s important to remember that comets don’t always perform as expected. Any prediction of a comet’s brightness is subject to change, sometimes radically. I’ve seen a few wax much brighter than expected, while others have gone nowhere but downhill. More needs to be known about C/2012 S1′s orbit before an accurate forecast can be made. Let’s just say things look very promising for now.
One other interesting tidbit about C/2012 S1 (ISON) is that its orbit appears very similar to the Great Comet of 1680 also known as Kirch’s or Newton’s Comet. The two may even be related. Kirch’s comet was discovered on November 14, 1680 by German astronomer Gottfried Kirch. After passing extremely close to the sun, it brightened so much it was plainly visible to the naked eye in mid-afternoon in early December.
One eyewitness report described it as having a “very fiery tail” that stretched 70 degrees long or more than 2/3 the way from horizon to zenith. Newton was working on his great treatise “Principia” at the time and used the comet’s motions to test the predictions of his theory of gravity.
Will C/2012 S1 (ISON) become a Great Comet, too? I’ll look into my crystal ball when more data becomes available.