Jan. 1, 2008
The article below was written in mid-December. I've left it unchanged, though two readers justifiably reproached me for describing Comet Holmes as "blazing away." Truth be told, "blazing" is appropriate for a star, but not for something as diffuse as Comet Holmes.
As the year 2008 opens, Holmes is still estimated to be magnitude 3.5 — nearly as bright as at its first outburst. But that light is spread out over roughly ten times the area of sky covered by the full Moon, giving it a fairly low surface brightness. So while Holmes is quite striking under pristine dark skies, it's difficult to see from typical suburban locations.
Meanwhile, Comet 8P/Tuttle has brightened dramatically in the past two weeks. It was estimated to be magnitude 6.0 or brighter at the end of December — just one-tenth the overall brightness of Holmes. However, it's fairly small and concentrated, making it an easy telescopic target in all but the worst skies. But you're likely to need fairly dark skies to see this comet through small binoculars or with just your unaided eyes.
Regardless of how dark your skies are and what instruments you use, both comets are now definitely harder to see than M31, the Andromeda Galaxy, but considerably easier than M33.
Dec. 12, 2007
With Comet Holmes still blazing away nearly as bright as ever, it's easy to forget that another bright comet is crossing the far-northern sky.
Although no match for Holmes, Comet 8P/Tuttle is now visible through 10×50 binoculars under dark skies. A telescope may be required in the suburbs.
To help you find the comet, we have prepared two printable finder charts in PDF format. Comet positions on both charts are shown for 0h in Universal Time — equal to 7 p.m. on the preceding date in Eastern Standard Time.
Click here to see the comet's path before Dec. 25.
Click here for a chart covering late December and all of January.
The comet is predicted to peak in brightness around the New Year, as shown at right. And recent magnitude estimates indicate that the predictions are pretty much on target.
So far, the comet appears to be a modest-sized, medium-faint circular blob. But comets are famously unpredictable, as Holmes has just demonstrated in the most dramatic fashion. So Comet Tuttle bears watching too, despite its current rather bland appearance. Nobody can predict when or if it will sprout a tail — or even undergo a dramatic outburst like Comet Holmes.
Tuttle moves across the sky at a fairly sedate pace in early December, but it picks up speed as it makes its closest approach the Earth — just 23.5 million miles away — on New Year's Day. Despite the full Moon, the comet should be a fairly easy target by the time it crosses the W of Cassiopeia from December 20-25. And around 0h UT on December 31st (7 p.m. Dec. 30 EST), the comet passes through the outer edge of Messier 33, the Triangulum Galaxy. (Think photo-op!)
The comet moves south quite rapidly during January, passing through Pisces, Cetus, Fornax, and then into the southern reaches of Eridanus. It will become a challenging target for northern observers around the middle of the month, when it's swallowed in the glow of the first-quarter Moon.
For more information on Comet Tuttle, see the January issue of Sky & Telescope. And don't miss the sidebar on the checkered career of Horace Tuttle: comet hunter, war hero, and embezzler.