Sunday, October 10, 2010

Comet Hartley 2

Comet Hartley 2 (officially 103P/Hartley) is a small comet in the sky right now which may brighten to naked-eye visibility (barely at magnitude 5) by the time of its closest approach on October 20.  It will easily be visible with binoculars if you know where to look.

At its closest approach to Earth on October 20, it will be some 11 million miles away (about 47 times the distance from the Earth to the Moon).  The comet will reach perihelion (peri = "around" and helios="Sun" - the closest approach to the Sun) on October 28.

The comet was discovered by Australian astronomer and comet hunter Malcolm Hartley in 1986.  In has an orbital period of 6.46 years.  It doesn't appear to have much of a tail in recent images, just a blue-green glow surrounding the cometary nucleus.

Tonight (October 10), the comet will be near h-Persei (h is eta) in the constellation of Perseus.  At 9:00 pm, this star will be in the northeast almost 40° above the horizon (if you extend your arm and make a fist, your fist held sideways will cover about 10° of the sky).  Note below that h-Persei (circled) is directly below the distinctive W-shaped constellation of Cassiopeia.  Scanning with binoculars in this region should reveal the faint glow of the comet.

If you plan on looking for the comet near closest approach on the 20th, wait until 11:00 pm or after before going out since it will be too low in the sky at 9:00 pm.  The 19th is probably best since it will be close to Capella, a bright, easy-to-find star.  At 11:00 pm on the 19th, Capella will be about 35° high in the northeastern sky (slightly east of northeast).  The comet should be a bit to the right of Capella.

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