Essential Information

Location
Royal Observatory

08 Oct 2010

On 20 October 2010, Comet Hartley 2 (103P/Hartley) will pass within about 11 million miles (0.12 AU) of the Earth. This will be its closest approach since it was discovered in 1986, and one of the closest approaches of any comet in the last few hundred years. At this time, the comet should be visible in the constellation Auriga.

Image: Hartley 2 in Cassiopeia, 28 Sep 2010 (crop). Credit: NASA/MSFC/Bill Cooke, NASA's Meteoroid Environment Office.

Astrophotography opportunity

There will be a great opportunity for astrophotographers between 7-9 October as the comet passes close to the beautiful Double Cluster in Perseus. It is then expected to pass near the open cluster NGC 1528, also in Perseus, by 14 October. Don't forget to enter your photographs of the comet in the 2011 Astronomy Photographer of the Year competition which opens in January.

Viewing Hartley 2

Meanwhile over the next few days Hartley 2 should become increasingly visible with the aid of binoculars or a small telescope, and possibly even to the naked eye.

The comet is diffuse (its light is spread out over a wide area) so to see it you need a dark sky location free of city lights. The technique of averted vision - looking slightly to one side rather than straight on - is also helpful in locating faint objects. The comet will probably appear as a grey smudge of light or as a faint, fuzzy star. Heavens-Above.com has a useful locator chart.

After 10 October the Moon will start to make it harder to see the comet, so until 20 October best viewing time will be after moonset.

EPOXI mission

On 28 October, the comet will reach perihelion (closest approach to the Sun). Finally, on 4 November, NASA's EPOXI mission (previously Deep Impact) will fly by the comet, with a closest approach of 435 miles.

It's estimated that Hartley 2 will next come to perihelion in 2017, around 20 April.