New comet may become brilliant in 2013
Red indicator bars show the extremely faint image of Comet ISON, taken the night after its discovery on September 21.
Photo courtesy E. Guido, G. Sostero and N. Howes
By Terence Dickinson, SkyNews Editor
Astronomy enthusiasts are buzzing about a faint and distant comet discovered by two amateur astronomers, Vitali Nevski of Belarus and Artyom Novichonok of Russia using a 16-inch telescope in Russia on September 21. Officially designated C/2012 S1, the comet is better known as Comet ISON, the acronym for the Russian observatory involved in the discovery.
Comet ISON is currently located beyond the orbit of Jupiter, but is is heading for an extreme close encounter with the Sun in November 2013 when it will pass 1.1 million kilometres from the solar surface—a close shave in astronomical terms. The fierce heating it experiences then could vaporize billions of tonnes of the comet’s ices, transforming it into a brilliant naked-eye object with a long streaming tail...or not. Comet ISON could be destroyed by the encounter, as dozens of comets with similar orbits have before.
To predict what the comet will look like to an observer on Earth, astronomers need to know two basic facts about a comet: its orbit (where it is now and where it is going), and its composition. Tracking the comet by telescope provides the first one with good accuracy, and we know that when it is closest to Earth in late 2013, Comet ISON will be in the morning sky and potentially visible from Canada.
The second one—the composition—is much tougher. And it is the nature of the comet’s ices and the dust imbedded in the ice that determines the size of the comet’s tail and thus its brightness.
Comets can, and often do, fizzle. Comet Elenin of 2011 was a recent example. It simply got fainter and fainter until it disappeared. Astronomers suspect that Comet ISON is a “new” comet coming into the inner solar system for the first time from the Oort Cloud beyond Neptune, the solar system’s comet reservoir. Therefore, this could be Comet ISON’s first encounter with the Sun’s intense heat.
Comet Kohoutek of 1973, hyped as the Comet of the Century, was just such a new comet. After it was hugely hyped by the media, it turned out to be less than one-tenth of one percent of its earlier predicted brightness—one of the biggest comet flops in the history of astronomy.
On the other hand, there was a brilliant comet in 1680 with an orbit very similar to this comet, opening a possibility that Comet ISON may in fact be this previous comet—or part of it—coming back. But for now, brightness predictions for November 2013 are just guesses, and at this stage, hardly even educated guesses. And the hype has already begun.
Comet as Bright as the Full Moon!!??
Several generally reliable news sources, among them CBC News, the London Telegraph in the UK, and Canada’s National Post, have stated that Comet ISON could reach (or even exceed) the brightness of the full Moon. Making such a claim without elaboration is a sound bite that plants a distorted image in the public’s mind.
Why? A comet as bright as the full Moon would be 10,000 times brighter than Comet Hale-Bopp was at its best in early spring 1997. A picture published in SkyNews around that time, shot from downtown Toronto, shows Hale-Bopp in the sky beside the CN Tower. It was an elongated smudge, but you could see it amid the glow of big-city light pollution. Now picure this: A comet 10,00 times brighter would cast shadows! No comet in recorded history has ever been close to that brilliance in a dark sky—and it won’t happen this time either.
Essential background info unstated in the sound bite mentioned above is that if Comet ISON reaches that brightness (highly uncertain), it will remain at that level for only a few hours as it passes closest to the Sun. But the key point is that the comet will just be the width of two fingers (held at arm’s length) away from the Sun, deep in solar glare in a bright daytime sky. Doesn’t matter much if the comet as bright as the full Moon. The Sun will be right beside it, one million times brighter.
The history of comets is filled with inflated expectations. So here we go again. A similar scenario played out in 1973, the year leading up to Comet Kahoutek’s flop. I’m not saying that Comet ISON will be a flop. It has the potential to be a wonderful comet. But as David Levy says, “Comets are like cats. They both have tails and they do what they want.”
Watch this space for further developments.