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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