Year of the Comet: Third comet set to make appearance in April 2013

Year of the Comet: Third comet set to make appearance in April 2013





February 2, 2013


SIGNS IN THE SUN, MOON AND STARS: GREEN COMET LEMMON - 2013
could be the Year of the Comet. Comet Pan-STARRS is set to become a
naked eye object in March, followed by possibly-Great Comet ISON in
November. Now we must add to that list green Comet Lemmon (C/2012 F6).
“Comet Lemmon is putting on a great show for us down in the southern
hemisphere,” reports John Drummond, who sent us a picture from Gisborne,
New Zealand: “I took the picture on Jan. 23rd using a 41 cm (16 in)
Meade reflector,” says Drummond. “It is a stack of twenty 1 minute
exposures.” That much time was required for a good view of the comet’s
approximately 7th-magnitude coma (“coma”=cloud of gas surrounding the
comet’s nucleus). Lemmon’s green color comes from the gases that make up
its coma. Jets spewing from the comet’s nucleus contain cyanogen (CN: a
poisonous gas found in many comets) and diatomic carbon (C2). Both
substances glow green when illuminated by sunlight in the near-vacuum of
space. Discovered on March 23rd 2012 by the Mount Lemmon survey in
Arizona, Comet Lemmon is on an elliptical orbit with a period of almost
11,000 years. This is its first visit to the inner solar system in a
very long time. The comet is brightening as it approaches the sun; light
curves suggest that it will reach 2nd or 3rd magnitude, similar to the
stars in the Big Dipper, in late March when it approaches the sun at
about the same distance as Venus (0.7 AU). Northern hemisphere observers
will get their first good look at the comet in early April; until then
it is a target exclusively for astronomers in the southern hemisphere. EP


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