Comet Hartley Disappointing
Perfectly positioned in Cassiopeia, but fainter than expected
By Terence Dickinson
Riding high in the evening sky, Comet Hartley could have been a fine binocular comet, but as of the first week of October, it is running a full magnitude below predictions, with virtually no tail—even in the images taken by the Hubble Space Telescope. Comets can surprise, and Hartley could brighten dramatically, but so far, it is a faint, slightly elongated fuzz in binoculars.
On October 3, when the accompanying image was taken at my observatory, the comet appeared as a small diffuse patch in 12x36 image-stabilized binoculars. I estimated it at magnitude 6.7, more than a full magnitude below the predicted 5.6. It appeared elongated, but with a weak nucleus and no tail. The image, taken with a modified Canon 7D on a Hutech 71mm f/3.5 astrograph, offers a nice colour contrast for the bluish comet, with the Pac-Man Nebula (NGC281), at right, and the star cluster NGC457, at top left edge.
On the evening of October 7, watch for the comet beside the famous Double Cluster near Cassiopeia. Each night after that, it will move progressively two degrees farther from the “W” of Cassiopeia. Detailed charts are on pages 26-27 of the September/October SkyNews. Earlier brightness predictions suggested the comet would be about magnitude 4.5 in mid-October, but expect it to be more on the order of magnitude 6.
Photo and note added October 8
A beautiful alignment of Comet Hartley with the Perseus Double Cluster on the night of October 7/8 occurred under completely clear skies here at NightWatch Observatory. The impression mentioned above was reinforced with the comet appearing as a dim puff in image-stabilized 12x36 binoculars, and only slightly more distinct in larger glasses. With no tail and running more than a magnitude below predictions, the 6.5-magnitude comet is regarded by many observers (me included) as a flop visually, but a nice photographic target, especially this night. A 7-inch f/2.8 Takahashi astrograph was used for this single 2-minute exposure taken a half hour after midnight EDT with modified Canon 7D at 1600 ISO.
Update added October 10
Comet Hartley remains faint and diffuse in binoculars and small telescopes—a small oval 6th-magnitude diffuse puff of smoke, difficult in binoculars except under dark, rural skies. Indeed, many readers located under urban or suburban light polluted skies have reported that the comet is not visible in binoculars.