A comet is heading for an unusually close approach to Earth that will bring it within range of small telescopes, binoculars, and maybe even the naked eye.
The comet is called Hartley 2 or, more formally, 103P/Hartley 2. It was discovered by astronomer Malcolm Hartley of Siding Spring Observatory in Australia on March 15, 1986. It was quickly recognized as a periodic comet that takes just over 6 years to orbit the sun and became the 103rd known periodic comet. Although Hartley 2 was seen at subsequent returns in 1991, 1997, and 2004, the 2010 return is definitely a special one.
Comet Hartley 2 will be passing 11 million miles from Earth on October 20. Although this may not seem particularly close, it is fairly rare for comets to actually pass this close or closer to our planet. Out of several thousand known comets, only about two dozen have passed closer to our planet during the last three centuries.
A bonus of this appearance is that the closest approach to Earth occurs about a week before the comet is also at its nearest distance from the sun. The result is that the comet will steadily brighten during the next month and could become a naked-eye object for people observing under dark skies during the second half of October. The comet will also increase in size and could attain a diameter close to the width of the moon…maybe larger. This does not mean the comet will be as bright as the moon, just the same diameter in the sky.
The comet is bringing some additional excitement. The Deep Impact spacecraft that flew passed periodic comet 9P/Tempel 1 in 2005 will be passing just 620 miles from comet Hartley 2 on November 4 in what has been designated the Deep Impact Extended Mission. The spacecraft carries two telescopes with digital color cameras and an infrared spectrometer. The latter instrument will determine the chemical composition of outbursts of gas from the comet's nucleus. The cameras began acquiring images on September 5 and should continue through November 25.
For more info and images: Check out Gary W. Kronk's 103P/Hartley 2 web page at http://cometography.com/pcomets/103p.html
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