Summary

After a year of “will it, won’t it”, C/2021 A1 (Leonard) developed into the best comet of 2021. While a difficult object to observe when at its brightest due to a small solar elongation, several outbursts resulted in a peak brightness between magnitude 2.5 and 3.0. As the year begins, the comet has faded to around magnitude 5.0. The comet remains very dynamic with imagers following nightly changes in its coma and tail. Speaking of tails, some images are showing a tail nearly 40 deg in length! Northern observers will only have a few more days to observe Leonard while southern hemisphere observers should be able to follow Leonard throughout the month.

Leonard may be the brightest comet out there, but it isn’t the only one in the range of modest backyard equipment. 19P/Borrelly is around 8-9th magnitude in the evening sky. 67P/Churyumov-Gerasimenko and C/2019 L3 (ATLAS) are also at a similar brightness near opposition. Slightly fainter comets (magnitude 10-11) include 6P/d’Arrest, 104P/Kowal, and C/2017 K2 (PANSTARRS).

Since December 1, the ALPO Comets Section has received 118 magnitude estimates and 120 images and sketches of comets C/2021 A1 (Leonard), C/2019 T4 (ATLAS), C/2019 L3 (ATLAS), 104P/Kowal, 67P/Churyumov-Gerasimenko, 29P/Schwassmann-Wachmann, 19P/Borrelly, 6P/d’Arrest, and 4P/Faye. Observations were contributed by Michael Amato, Salvador Aguirre, Dan Bartlett, Michel Deconinck, Lukas Demetz, Walter Elias, J. J. Gonzalez, Christian Harder, Jan Hattenbach, Carl Hergenrother, Eliot Herman, Michael Jäger, Kardasis Manos, Luis Alberto Mansilla, Frank McCague, Martin Mobberley, Michael Olason , Uwe Pilz, Olivier Planchon, Efrain Morales Rivera, Michael Rosolina, Gregg Ruppel, Chris Schur, Leandro Sid, Willian Souza, Tenho Tuomi, Jim Twellman, Chris Wyatt, and Skygems Observatory.

The monthly ALPO Comet News PDF can be found here. A shorter version of this report is posted on a dedicated Cloudy Nights forum. All are encouraged to join the discussion over at Cloudy Nights.

- Carl Hergenrother

Summary

It is now or never for C/2021 A1 (Leonard). Currently magnitude 6.5, Leonard has the potential to become a few magnitudes brighter as it passes 0.23 au from Earth on December 12. Complicating any forecast of how bright or observable it might get are a very low solar elongation (down to 15 degrees), uncertainty in the effect of dust forward scattering to enhance Leonard’s brightness, and signs that the comet is fading or perhaps even breaking up. This is an object well worth watching in the morning sky from the northern hemisphere during the first half of the month and in the evening sky during the second half of December (though at that time it will be much easier to observe from the southern hemisphere).

Other comets brighter than 10th magnitude in December include C/2019 L3 (ATLAS), 19P/Borrelly, and 67P/Churyumov-Gerasimenko.

The monthly ALPO Comet News PDF can be found here. A shorter version of this report is posted on a dedicated Cloudy Nights forum. All are encouraged to join the discussion over at Cloudy Nights.

- Carl Hergenrother

Summary

After an exciting 2020 for comets, 2021 seemed to be a bit of a letdown. Well, it may have taken most of the year to get going, but 2021 is finally picking up steam. We now have three comets brighter than magnitude 10. C/2021 A1 (Leonard) may brighten to the verge of naked eye visibility (for those under very dark skies) by the end of the month. It should get even brighter next month when it could reach 4th magnitude or perhaps even brighter. C/2019 L3 (PANSTARRS) and 67P/Churyumov-Gerasimenko will be around magnitude 9 this month. 

If you’ve never observed 29P/Schwassmann-Wachmann before, this is a great time to start. The Centaur comet has experienced a succession of outbursts since late September. As a result, it is brighter than it’s been in years with visual observers placing it between magnitude 10 and 11.

Two recently discovered comets have the potential to be nice small telescope objects when they arrive at perihelion over the next few years. C/2021 S3 (PANSTARRS) may reach 8th magnitude in 2024 while C/2021 T4 (Lemmon) could be a 9th magnitude object in 2023.

Comets Section News

From October 1 through the first week of November, the ALPO Comets Section received 125 visual and CCD magnitude measurements and 80 images and/or sketches from Dan Bartlett, Michel Besson, Denis Buczynski, Dan Crowson, Michel Deconinck, J. J. Gonzalez, Christian Harder, Carl Hergenrother, Eliot Herman, Gianluca Masi, Martin Mobberley, Mike Olason, Ludovic Prebet, Efrain Morales Rivera, Chris Schur, Tenho Tuomi, Dennis Wilde, and Chris Wyatt of the following comets: C/2021 K1 (ATLAS), C/2021 A1 (Leonard), C/2020 T2 (Palomar), C/2020 F5 (MASTER), C/2019 T4 (ATLAS), C/2019 LD2 (ATLAS), C/2019 L3 (ATLAS), C/2019 F1 (ATLAS-Africano), C/2017 K2 (PANSTARRS), 433P/(248370) 2005 QN173 ,429P/LINEAR-Hill, 424P/La Sagra, 284P/McNaught, 246P/NEAT, 230P/LINEAR, 179P/Jedicke, 132P/Helin-Roman-Alu, 119P/Parker-Hartley, 113P/Spitaler, 104P/Kowal, 97P/Metcalf-Brewington, 94P/Russell, 67P/Churyumov- Gerasimenko, 57P/du Toit-Neujmin-Delporte, 29P/Schwassmann-Wachmann, 19P/Borrelly, 8P/Tuttle, 7P/Pons-Winnecke, 6P/d’Arrest, and 4P/Faye.

The monthly ALPO Comet News PDF can be found here. A shorter version of this report is posted on a dedicated Cloudy Nights forum. All are encouraged to join the discussion over at Cloudy Nights.

- Carl Hergenrother

Summary

Magnitude 9 to 10 may not be everyone’s idea of “bright” when it comes to comets. After months of no comets getting brighter than 10th magnitude, we finally have a few objects breaking the 10th magnitude barrier. The target of the European Space Agency’s Rosetta mission, 67P/Churyumov-Gerasimenko may brighten to around magnitude 9 this month. It will be observable from both hemispheres in the morning sky. 8P/Tuttle will start the month around 8-9th magnitude but is limited to southern hemisphere observers. C/2019 L3 (PANSTARRS) could become brighter than magnitude 10 though it will mainly be a northern object.

29P/Schwassmann-Wachmann experienced 4 outbursts in quick succession in late September. As a result, it is brighter than it has become in years with visual observers placing it between magnitude 10 and 11.

We continue to watch C/2021 A1 (Leonard) develop as it heads towards a December encounter with Earth. Recent observations show a rapid brightening trend, so imagers and large aperture visual observers are encouraged to observe it this month as it may brighten to magnitude 11 by the end of the month.

Comets Section News

During September, the ALPO Comets Section received 51 images and/or sketches from Dan Bartlett, Denis Buczynski, Eliot Herman, Gianluca Masi, Martin Mobberley, Uwe Pilz, Efrain Morales Rivera, Gregg Ruppel, and Chris Schur and 67 visual and CCD magnitude measurements from Michel Deconinck, J. J. Gonzalez, Mike Olason, and Chris Wyatt of the following comets: P/2021 Q5 (ATLAS), C/2021 O3 (PANSTARRS), C/2021 A1 (Leonard), C/2020 T2 (Palomar), C/2020 PV6 (PANSTARRS), C/2020 F5 (MASTER), C/2019 O3 (PANSTARRS), C/2019 L3 (ATLAS), C/2019 F1 (ATLAS-Africano), C/2018 U1 (Lemmon), C/2020 T2 (PANSTARRS), C/2017 K2 (PANSTARRS), 284P/McNaught, 193P/LINEAR-NEAT, 106P/Schuster, 67P/Churyumov-Gerasimenko, 29P/Schwassmann-Wachmann, 19P/Borrelly, 15P/Finlay, 8P/Tuttle, 7P/Pons-Winnecke, 6P/d’Arrest, and 4P/Faye.

In addition to observations submitted directly to the ALPO, we occasionally use data from other sources to augment our analysis. We would like to acknowledge with thanks observations submitted directly to the ALPO as well as those originally submitted to the International Comet Quarterly, Minor Planet Center, and COBS Comet Observation Database. We would also like to thank the Jet Propulsion Laboratory for making available their Small-Body Browser and Orbit Visualizer and Seiichi Yoshida for his Comets for Windows programs that is used to produce the lightcurves in these pages. And last but not least, we’d like to thank Syuichi Nakano and the Minor Planet Center for their comet orbital elements, the asteroid surveys and dedicated comet hunters for their discoveries, and all of the observers who volunteer their time to adding to our knowledge of these amazing objects. 

The monthly ALPO Comet News PDF can be found here. A shorter version of this report is posted on a dedicated Cloudy Nights forum. All are encouraged to join the discussion over at Cloudy Nights.

- Carl Hergenrother