Comet Hartley 2 and Earth to Pass at 11 Million Miles on October 20 2010

Astronomers and interested amateurs often turn to the night skies in hopes of discovering something new or seeing one of the celestial wonders which make up our universe.

On October 20, 2010 another anticipated space event will be occurring. This day the Earth will experience a close pass-by with Comet Hartley 2 at just over 11 million miles in distance. While comets frequently come and go without much notice, this one is an event because of its unusually close proximity to Earth on this particular orbit.

Meterologist and Hayden Planetarium instructor Joe Rao reports on that Comet Hartley 2 should be easily visible using small telescopes, binoculars and, in dark skies, even be seen by the naked eye.

Hartley 2 was discovered by astronomer Malcolm Hartley in 1986. The comet was discovered while viewing from Australia and the photographic images taken showed the comet as a faint object with a small bit of a tail. Hartley 2 is extremely dim and Rao describes the comet as “about 25,000 dimmer than the faintest stars that can be seen with the naked eye.” After the discovery of the comet, Hartley brought his findings to a Cambridge, Massachusetts facility where Brian Marsden of the Smithsonian Astrophysical Observatory calculated Hartley 2’s orbital patterns. (

Marsden calculated that it takes Comet Hartley 2 six and one half years to orbit the sun. Since the initial discovery, Hartley 2 has been studied in 1991, 1997 and 2004. So the comet is seen fairly regularly, however when dimness and distance are coupled, the event is not a huge deal.

What is unique about 2010 is the proximity that the comet will come to both the Earth. The closeness which will occur is rare and projections are Hartley 2 will reach its closest point at 3 p.m. ET on Wednesday, October 20 at 11.2 million miles away. This is an unusual event not only for Hartley, but any comet in general. However due to the comet’s small size, it probably won’t get the fanfare or provide the impressive show that another comet, such as the famed Halley’s Comet, would.

Rao describes “Astronomers use magnitude to define the brightness of sky objects; the lower the magnitude, the brighter the object. The brightest stars are zero or first magnitude, while the faintest stars are sixth magnitude.  Current expectation is that the comet will reach a peak magnitude of perhaps 4.4 at the time of its closest approach. However, around that time the comet will probably appear very large in overall apparent size, perhaps similar to the apparent size of the full moon.” (

Despite its small size, space enthusiasts should enjoy seeking out Hartley 2. Viewers should look for a circular patch of light; if a tail is visible, it will be thin and small. Unfortunately the moon may interfere with the view, but after the moon sets could provide the optimal viewing times.

In related space news, also reports that NASA’s Deep Impact spacecraft will be taking lots of close up photos of Comet Hartley 2 as it makes a near approach on November 4 at an amazingly close range of 430 miles.