A new visitor will be gracing the morning sky through the end of June. The visitor is formally designated C/2009 R1 (McNaught), but most astronomers are just calling it comet McNaught.
The comet was found by Robert H. McNaught, the British-Australian astronomer who has managed to discover more than 50 comets from Siding Spring Observatory in Australia during the last couple of decades. This particular comet was found on September 9, 2009.
Comet McNaught is heading toward perihelion (it's closest approach to the sun), which will occur on July 2. It will then be about 38 million miles from the sun, about the same distance as the planet Mercury.
Numerous amateur and professional astronomers have been acquiring photographs of the comet on a daily basis for the last month. The Author has acquired several images, one of which graces this article. This image was acquired on the morning of June 15 from my backyard observatory in rural Illinois.
How bright will this comet be?
A couple of days ago the first reports came forth indicating the comet had become visible to the naked eye, although the observations were made in rural and mountain regions where there is little or no light pollution from cities. With slight light pollution to the northeast of my site (thanks to a Wal-Mart about four miles away), I have not been able to see the comet with just my eyes, although it is a simple object in binoculars.
For the remainder of June, the comet is expected to continue brightening, but, at the same time, it will be dropping into morning twilight. Although it will certainly remain a binocular object for most of the next two weeks, there is still some uncertainty as to its expected maximum brightness...meaning we don't really know if it will become a prominent naked-eye object or not.
A major factor in a comet becoming a prominent naked-eye object is its tail. Comets can typically display two tails: gas and dust. Gas tails are generally straight and narrow, but they are bluish in color, which makes them difficult to see against the dark sky. For the last month, comet McNaught has been displaying a gas tail, which has been rather prominent on photographs and has recently been measured as 7-10 degrees long or 14 to 20 times the apparent width of the moon. Dust tails are generally fan-shaped and are yellow in color. This color makes them more suitable for naked-eye viewing. Comet McNaught has only been displaying a stubby dust tail. Although it is slowly getting longer, no one can say just how long this tail might become.
Although we can't say how bright or prominent comet McNaught might become during the next two weeks, we can say that the comet should remain a binocular object in the northeast sky visible about an hour before sunrise. It is currently located around the middle of the constellation Perseus and will enter the constellation Auriga on June 20. The comet will draw closer to the northeast horizon as each day passes, so a clear view of the horizon will be necessary. This morning it was about 20 degrees above the horizon. It will have an altitude of about 15 degrees on June 20 and about 5 degrees on June 25.
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