On Oct. 20, Comet Hartley 2 will pass just over 11 million miles (18 million km) from Earth. During October it should be easily visible in small telescopes, binoculars and — from sites with dark enough skies — even with the naked eye.
As October begins, Comet Hartley 2 will be in the constellation of Cassiopeia, which at dusk will be positioned halfway up in the northeast sky; through Oct. 5 it will be passing below and to the right of the famous “W”-shaped formation composed of five bright stars.
The comet then moves into the constellation of Perseus on Oct. 6 and before dawn on the morning of Oct. 8, it will be situated only 0.7 degrees below and to the right of the famous Double Star Cluster. The cluster supposedly marks the sword handle of Perseus and is often touted as one of the most impressive star clusters in the entire sky.
On the morning of Oct. 10, the comet will appear to almost touch the 4th-magnitude star, Eta Persei. On Oct. 17, it will enter the boundaries of the constellation Auriga, and on the morning of Oct. 18, Hartley 2 will be about 1.2 degrees above and to the right of the star Epsilon Aurigae and 3 degrees below and to the right of the brilliant zero-magnitude star Capella.
Between Oct. 15 and 20, within about a half hour of 4:00 a.m. local time, the comet will be passing almost directly overhead.
Even after Hartley 2 makes its closest approach to Earth, it will become part of another close approach of a different kind. On Sept. 5, more than five years after its July 4, 2005, rendezvous with Comet Tempel 1, NASA’s Deep Impact spacecraft will begin beaming down the first of more than 64,000 images it’s expected to take of Comet Hartley 2.
The spacecraft will continue imaging Hartley 2 during and after its closest approach on Nov. 4, when it will pass to within 430 miles (692 km) of the comet’s nucleus, providing an extended look at the comet.