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Sungrazer Comet The Remarkable Case of Lovejoy 36 May 2012 sky & telescope Despite the odds against it, Comet Lovejoy survived its swing by the Sun and became one of the most spectacular comets in the past few decades. john e. bortle The comet left only the vaguest smudge on the November 27th discovery images. Nevertheless, it was enough for keen-eyed Australian amateur Terry Lovejoy to pick it out from background stars. Although it didn’t look like much at the time, only three weeks later it would become the most spectacular comet in years! And its discovery gave us an unprecedented opportunity to study a sungrazing comet before, during, and after its brush by the Sun’s surface. Comet Lovejoy, C/2011 W3, was offi cially announced on December 2nd (see page 41). But the real rush of excitement came a few days later when its orbit revealed it to be a sungrazer that would rendezvous with the Sun on December 16th, passing within a scant 200,000 kilometers (125,000 miles) of its visible surface. Among the most extraordinary of all comets, the family of sungrazers is thought to be the remnants of a huge comet that broke apart millennia ago, and it might even have been the one Aristotle wrote about in the year 371 BC that had a tail that spanned a third of the heavens. Progressive fragmentation at each subsequent swing by the Sun broke up the major fragments of this progenitor to spawn a host of ever smaller pieces. When near perihelion, the largest of these surviving pieces become so brilliant that they are visible in the daytime and thereafter may unfurl tails as long as 60°. Some Sky & Telescope readers will undoubtedly recall the brilliant sungrazer Comet Ikeya-Seki in 1965, which was one of the most spectacular comets of the 20th century. In addition to these showpiece comets, several solarmonitoring satellites have discovered more than a thousand pygmy sungrazers during the last three decades. They are the fl otsam from the repeated break-ups experienced by the larger pieces at previous perihelion passages, and they now form an almost steady stream of debris spread along the parent comets’ orbits. These fragile fragments are more than a thousand times fainter than sungrazers such as Comet Ikeya-Seki and are unable to withstand the Sun’s furious heat and gravity. Not one of them has been observed to survive its fi ery brush with the Sun, typically vaporizing completely in the fi nal hours before perihelion. At the outset it seemed that Comet Lovejoy’s intrinsic faintness grouped it with the pygmy sungrazers, but the internet was still set abuzz by an early suggestion that the comet might reach magnitude –7 before its demise in the solar inferno. Nevertheless, the faintest sungrazer seen to survive its perihelion had an intrinsic brightness of about magnitude +7 or +8, or roughly a thousand times brighter than Comet Lovejoy. Thus, it seemed that the odds were all but nil that the comet would come through its rendezvous with the Sun unscathed. In the days leading up to Christmas 2011, Comet Lovejoy appeared increasingly spectacular as it rose higher in the Southern Hemisphere morning sky. This was the view on December 23rd. ROBERT H. MCNAUGHT
“I trust that most here appreciate that we are witnessing one of the most extraordinary events in cometary history.” John Bortle writing on the Comets Mailing List on December 16th after Comet Lovejoy had rounded the Sun. SkyandTelescope.com May 2012 37
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