This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
NASA's EPOXI spacecraft is closing in on a comet called Hartley 2 in advance of a November 4 flyby, but stargazers on Earth are already getting a fairly good look at the icy object, which is currently in the midst of an unusually close passage of Earth.
Hartley 2 is now only about 18 million kilometers from Earth, the closest it has been since the comet was discovered nearly 25 years ago, and on October 28, the comet will make its closest approach to the sun. Hartley 2, which orbits the sun in an elongated ellipse every 6.5 years, is named for Malcolm Hartley, an English-born astronomer who first spotted it from an Australian observatory in 1986.
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The comet is rather small, just over one kilometer in diameter, but may be visible to the naked eye under clear, dark skies, according to StarDate magazine, which has assembled a finder chart to locate Hartley 2 in the sky. (As always, a good pair of binoculars never hurts when trying to locate a relatively small, faint object.) Viewing the comet may be easier toward the end of the month, when Hartley 2 is closer to the sun and there is less moonlight in the night sky. Sky & Telescope made available a similar guide, which includes the path of the comet through the end of 2010 for more dedicated and better-equipped skywatchers.
EPOXI's impending flyby will bring the spacecraft to within about 700 kilometers of Comet Hartley 2 to investigate its structure and makeup. The planned rendezvous will not be the first comet encounter for the NASA probe. In 2005 the spacecraft, then known as Deep Impact, sent an impactor careening into Comet Tempel 1 to excavate a crater and get a glimpse of its composition.
Comet Hartley 2 as seen from EPOXI on October 1: NASA/JPL/UMD
