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.

Comet Hergenrother in outburst

Here's how Comet 168P/Hergenrother appeared on October 3, 2012, as recorded in a 13-frame stack of red-light images acquired with the Faulkes South telescope in Australia.

N. Howes / A. Tripp / E. Guido / G. Sostero

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.

Path of Comet Hergenrother

Comet 168P/Hergenrother crosses the northeast corner of the Great Square of Pegasus during the first half of October 2012. Tick marks indicate the comet's position at 0h on each date, which corresponds to the previous evening in the Americas. The faintest stars shown are magnitude 7.4. Click on the image for a larger version.

Sky & Telescope diagram

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:

Comet 168P/Hergenrother
Date Right ascension Declination
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.


Image of Paul Cox

Paul Cox

October 5, 2012 at 4:45 pm

We've been monitoring comet 168P/Hergenrother every night for the last month using the Slooh robotic telescopes. We noticed a fairly dramatic brightening again a few nights ago.

Prompted by this, I'll be broadcasting a free show on Saturday (4PM PDT/7PM EDT) where we'll be looking at live images of Hergenrother and a number of other current bright comets. I may hold a follow-up show 3hrs later at 7PM PDT.

Kelly - you would always be a welcome guest on any of the shows that illustrate many of your articles with live images of the objects you're writing about. It would be fascinating to hear from you while we're watching the live images!

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Image of Carl Hergenrother

Carl Hergenrother

October 8, 2012 at 1:56 pm

Kelly, thanks for producing such a great article on 168P. As a long-time S&T reader I've waited a long time for a discovery of mine to be highlighted by S&T. Last night (Oct. 8 UT) I was able to observe the comet in 10x50s and 30x125s at about magnitude 9.3.

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Image of Uncle Rod

Uncle Rod

October 14, 2012 at 9:19 am

Not bad, not bad at all. Despite haze and humidity, it was a sweet looking little thing with a pretty tail in my C8 and Mallincam Xtreme video camera. Visually, in my buddy's 15-inch Dobsonian, it was a little less impressive than I thought it would be. The tail was somewhat visible, but overally, dimmer than I figgered. No brighter than 11 was my guess...

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