As it passes through perihelion, Comet 168P/Hergenrother has undergone an unexpected outburst and brightened to about 10th magnitude. You'll find it crossing the Great Square of Pegasus, well placed for evening viewing.
Veteran astronomer David Levy once famously said, "Comets are like cats: they have tails, and they do precisely what they want."
An interplanetary visitor has once again proved him correct. Comet 168P/Hergenrother, which passed through the perihelion of its 6.9-year orbit on October 1st, has erupted unexpectedly and dramatically. Although no one expected it to become brighter than 15th magnitude, the comet has blossomed significantly — to better than 10th magnitude by one recent estimate.
Images show this periodic visitor to be almost starlike in appearance. When recorded yesterday by four observers using the 2-m Faulkes South telescope, Comet Hergenrother had a coma spanning about 3 arcminutes but a strong central condensation 8 arcseconds across. The team notes that it looked a little more "fluffy" than it did a week earlier.
This outburst puts the comet within range of backyard telescopes with apertures of 6 inches or larger. Right now Comet Hergenrother is 130 million miles (1.4 astronomical units) from the Sun but only 0.4 a.u. from Earth. You'll find it cruising slowly northward through the northeast corner of the Great Square in Pegasus. Moonlight won't be a problem for now, but you'll need a good star chart to distinguish it from surrounding faint stars.
Here are coordinates for the comet's position, at 0h Universal Time on each date, optimistically given for the next two weeks:
|Oct. 4||00h 07m 02s||+21° 36.5′|
|Oct. 5||00h 05m 28s||+22° 21.3′|
|Oct. 6||00h 03m 56s||+23° 05.1′|
|Oct. 7||00h 02m 25s||+23° 48.0′|
|Oct. 8||00h 00m 56s||+24° 29.8′|
|Oct. 9||23h 59m 28s||+25° 10.6′|
|Oct. 10||23h 58m 02s||+25° 50.3′|
|Oct. 11||23h 56m 38s||+26° 28.8′|
|Oct. 12||23h 55m 16s||+27° 06.3′|
|Oct. 13||23h 53m 57s||+27° 42.7′|
|Oct. 14||23h 52m 41s||+28° 17.9′|
|Oct. 15||23h 51m 27s||+28° 52.1′|
|Oct. 16||23h 50m 16s||+29° 25.1′|
|Oct. 17||23h 49m 09s||+29° 57.0′|
|Oct. 18||23h 48m 05s||+30° 27.9′|
|Oct. 19||23h 47m 05s||+30° 57.7′|
In November 1998, when Carl Hergenrother discovered this comet on images taken for the Catalina Sky Survey with a 16-inch (41-cm) Schmidt telescope, it was initially thought to have a parabolic orbit. But the comet's periodic nature soon became apparent, and Australian observer Dave Herald recovered it during the next perihelion passage in 2005.
Now Comet Hergenrother is again at perihelion — and it's putting on an unexpectedly satisfying show.