Watch spectacular comet on the Web

By Joe Rao

Skywatching columnist

updated 9:16 p.m. ET Jan. 12, 2007

Comet McNaught, the brightest comet to appear in our skies in more than 30 years, has been putting on a spectacular show in the eastern sky at dawn and the western sky at dusk this week.

And this weekend it might become even more brilliant. 

Ironically, the comet has also been a source of frustration for many skywatchers, because of its very low altitude. More often than not, the comet has been hidden either by clouds near the horizon, or nearby trees or buildings. For this reason, even some veteran observers have been stymied in their efforts to catch a glimpse of it.

But Comet McNaught is now also visible to armchair astronomers via images posted to the Internet from the Solar and Heliospheric Observatory spacecraft. And beginning next week, it will head rapidly south and likely become a spectacle for skywatchers in the Southern Hemisphere.

The comet was discovered by astronomer Robert H. McNaught Aug. 7 at Siding Spring Observatory, near Coonabarabran, New South Wales, Australia. 

McNaught discovered this comet when it was a few degrees east of the “head” of Scorpius, on CCD images obtained with the observatory’s Uppsala Schmidt telescope. The images had been obtained as part of the Siding Spring Survey, whose mission is to contribute to the inventory of potentially hazardous asteroids and comets that may pose a threat of impact and thus harm to civilization. 

McNaught described the comet — the 31st to bear his name — as magnitude 17.3, or about 25,000 times dimmer than the faintest object that human eyes can perceive without any optical aid.

When Brian Marsden at the Smithsonian Observatory in Cambridge, Mass., first calculated the orbit of Comet McNaught (now cataloged as C/2006 P1) on Aug. 8, it was based on only a handful of observations. As a result, this first computation suggested that the comet would come closest to the sun (called “perihelion”) in June 2007, and then not get much closer than about 145 million miles (233 million kilometers), or about the distance of the planet Mars.

As more observations of the comet arrived, however, Marsden refined its orbit, and on Aug. 11, he announced that it was likely to pass well within the Earth's orbit — a distance of just 15.9 million miles (25.6 million kilometers) — today. That's well within the orbit of Mercury. This would make the comet much brighter than most, but as a caveat, also potentially hide it in the sun's glare.

Mcnaught blossoms
From August into early November the comet steadily increased in brightness, but not enough to prevent it becoming lost in the evening twilight by mid-November.

Although still brightening, it appeared that the comet could be totally lost from view until it reappeared for Southern Hemisphere observers in the evening twilight skies late in January.  In addition, there was the opinion of several respected amateur and professional astronomers that the comet would completely disintegrate around the time of perihelion.

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The comet went unobserved for nearly six weeks but was successfully recovered in the twilight toward the end of December.

Since then the comet has continued to grow impressively in brightness. Just after the start of the New Year it was becoming clear that Comet McNaught could conceivably be a dazzling object when closest to the sun in mid-January. Indeed, as we pointed out in this column a year and a half ago, we were due for a spectacular comet.

Observers around the Northern Hemisphere have reported the comet shining as brightly as magnitude -3.0, or more than four times brighter than Sirius, the brightest star in the sky. 

This places Comet McNaught near the top of the list of the brightest comets that have appeared since 1935. But the brightest part of the display may be yet to come.

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