Comet 12P/Pons-Brooks has awakened again from its recent slumbers with a fresh outburst. It’s now bright enough to see in a modest telescope.
Periodic Comet 12P/Pons-Brooks remains in character as it heads toward perihelion next April. Famous for its unpredictable outbursts during previous appearances, it blew up again around October 5.2 UT, waxing nearly 100 times brighter (nearly 5 magnitudes!) compared to the night prior. Had you sought the comet on October 3rd, you might have looked in vain for a diffuse 14.5-magnitude object. By late the next evening, it had catapulted to magnitude 11.0 with a nearly stellar appearance, surrounded by a tiny, dense coma just half an arcminute across.
I hauled out my 15-inch between rain showers on Thursday night (Oct. 5th) and, using 64×, spotted the bright but slightly fuzzy nub at magnitude 11.3, with a degree of condensation of 8. I suspected a faint, short tail pointing east, as shown in the images.
Now, it's within reach of smaller scopes. The coma will expand, and the comet will gradually fade over time, but for now it's within grasp of a 6-inch telescope from dark skies. The scarce visitor — it only drops by every 71 years —is currently crossing northern Hercules, not far from the bright globular cluster M92.
Bonus! The Moon stays out of the way until around October 21st.
This is the fourth recorded outburst for 12P/Pons-Brooks this apparition. The first occurred on July 20th and was similarly bright. In the aftermath its coma expanded to resemble a horseshoe crab or, more fancifully, the Millennium Falcon from Star Wars. Two fainter flares followed on September 4th and 23rd, with respective magnitude increases of approximately 0.5 and 0.9.
The bursts are believed to originate from the outgassing of carbon monoxide and dioxide in the comet's core, which escape when solar heating weakens and fractures the overlying crust. The explosive eruption releases up to a million tons of dust, ice, and other detritus. Illuminated by sunlight the expanding cloud of debris swiftly ratchets up the comet's brightness.
Jose Manuel Pérez Redondo (Institut d’Alcarras, Spain) and Ben Wooding's students (St Mary's Primary School, Bridgend) discovered this second strong outburst in images made with the Faulkes Telescope North 2-meter telescope in Haleakala in Maui, Hawai'i. They and other members of the Comet Chasers education and outreach project and the LCO Outbursting Objects Key (LOOK) Project have been regularly monitoring the comet. You can read more discovery details in The Astronomers Telegram and an analysis of its current appearance by Richard Miles (British Astronomical Association) on the Comet 12P Observations site.
I hope you get a chance to see this fitful visitor, one of the best examples of what makes comets so much fun to watch.