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ALPO Comet News for November 2021

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#1 Carl H.

Carl H.

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Posted 07 November 2021 - 05:38 AM

ALPO COMET NEWS FOR NOVEMBER 2021
A Publication of the Comets Section of the Association of Lunar and Planetary Observers
By Carl Hergenrother

 

The monthly Association of Lunar and Planetary Observers (ALPO) Comet News PDF can be found on the ALPO Comets Section website @ http://www.alpo-astr....org/cometblog/. A shorter version of this report is posted here (minus the magnitude estimates, lightcurves, images, and other figures contained in the full PDF). The ALPO Comet Section welcomes all comet related observations, whether textual descriptions, images, drawings, magnitude estimates, or spectra. You do not have to be a member of ALPO to submit material, though membership is encouraged. To learn more about the ALPO, please visit us @ http://www.alpo-astronomy.org. We can also be reached at < comets @ alpo-astronomy.org >.

 

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, Deniis 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.

 

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.

 

Aperture Corrections to Magnitude Measurements
We try to include up to date lightcurves for most of the objects discussed in this report as well as applying aperture corrections to the visual observations. All magnitude estimates are affected by many factors including instrumental (aperture, focal length, magnification, type of optics), environmental (sky brightness due to moonlight, light pollution, twilight, aurora activity, zodiacal light, etc), cometary (degree of condensation, coma color, strength and type of gas emission lines, coma-tail interface) and personal (sensitivity to different wavelengths, personal technique, observational biases). The correction used here only corrects for differences in aperture [C. S. Morris, On Aperture Corrections for Comet Magnitude Estimates. Publ Astron Soc Pac 85, 470, 1973]. Visual observations are corrected to a standard aperture of 6.78 cm by 0.019 magnitudes per centimeter for refractors and 0.066 magnitudes per centimeter for reflectors. As our work develops, we will investigate the determination of personal corrections for each observer for each individual comet as well as for digital observations.

 

Comets Calendar for November 2021
Nov 02  – 67P/Churyumov-Gerasimenko at perihelion (q = 1.21 au, 6.4-year orbit, V~9, much more below)
Nov 02  – P/2005 L1 (McNaught) at perihelion (q = 3.14 au, 7.9-year orbit, V ~ ???, Not seen since discovery in 2005, missed at return in 2013 and so far in 2021 so much be much fainter than in 2005 when it peaked at V ~ 16)
Nov 03  – C/2018 U1 (Lemmon) at perihelion (q = 4.99 au, long-period, V ~ 14-15)
Nov 03  – 70P/Kojima at perihelion (q = 2.01 au, 7.1-year orbit, V ~ 16-17)
Nov 04  – New Moon
Nov 11  – First Quarter Moon
Nov 12  – P/2021 N2 (Fuls) at perihelion (q = 3.80 au, 18.3-year orbit, V ~ 16-17)
Nov 13  – 132P/Helin-Roman-Alu at perihelion (q = 1.69 au, 7.7-year orbit, V ~ 13)
Nov 13  – C/2021 C6 (Lemmon) at perihelion (q = 3.27 au, long-period, V ~ 19)
Nov 13/14 – 8P/Tuttle passes 2.5 deg of bright galaxy Centaurus A
Nov 14  – C/2020 F7 (Lemmon) at perihelion (q = 5.33 au, long-period, V ~ 17)
Nov 16  – C/2019 L3 (PANSTARRS) passes ~0.1 deg of interacting galaxies NGC 2444-2445
Nov 16/17 – 8P/Tuttle passes 1.5 deg of bright globular cluster Omega Centauri
Nov 19  – Full Moon
Nov 19  – C/2021 A1 (Leonard) passes ~0.3 deg of 10th mag galaxy NGC 4395
Nov 22/23 – 19P/Borrelly passes within the Grus Quarter of galaxies
Nov 23/24 – C/2021 A1 (Leonard) passes between bright galaxies NGC 4631 (the Whale) and 4656 (the Crowbar)
Nov 24  – C/2019 L3 (PANSTARRS) passes ~1.5 deg of 9th mag globular cluster NGC 2419
Nov 27  – Last Quarter Moon
Nov 27  – 8P/Tuttle passes ~0.3 deg of open cluster NGC 5460
Nov 29  – C/2014 OG392 (PANSTARRS) at perihelion (q = 9.97 au, 42.8-year period, V ~ 19-20, active Centaur)
Dec 02  – C/2021 A1 (Leonard) passes ~0.1 deg of 6th mag globular cluster M3

 

Comets Brighter Than Magnitude 10

 

C/2021 A1 (Leonard)

 

Discovered 2021 January 3 by Greg Leonard of the Catalina Sky Survey with the 1.5-m on Mount Lemmon
Dynamically old long-period comet

 

Orbit (from Minor Planet Center, MPEC 2021-U109)

 

    C/2021 A1 (Leonard)                                                        
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2022 Jan. 3.30021 TT                                  Rudenko                
q   0.6152629            (2000.0)            P               Q                 
z  -0.0000348      Peri.  225.09233     +0.63774032     +0.29161232            
 +/-0.0000011      Node   255.89556     +0.72791449     -0.53080431            
e   1.0000214      Incl.  132.68632     -0.25184875     -0.79574433            
From 1228 observations 2020 Apr. 11-2021 Oct. 27, mean residual 0".6.          

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

C/2021 A1 (Leonard)                                               Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  11 51  +34 53   1.392   1.565    61M   UMa  10.2    41    0
2021 Nov 06  11 58  +34 30   1.314   1.402    63M   UMa   9.8    44    0
2021 Nov 11  12 07  +34 06   1.237   1.233    66M   CVn   9.3    47    0
2021 Nov 16  12 17  +33 38   1.159   1.059    68M   CVn   8.7    49    0
2021 Nov 21  12 30  +33 02   1.082   0.882    70M   CVn   8.1    51    0
2021 Nov 26  12 50  +32 02   1.006   0.702    70M   CVn   7.4    51    0
2021 Dec 01  13 21  +29 59   0.931   0.523    68M   CVn   6.4    49    0
2021 Dec 06  14 21  +24 28   0.859   0.356    59M   Boo   5.3    38    0

 

Comet Magnitude Formula (from ALPO and COBS data)

 

m1 =  7.4 + 5 log d + 11.7 log r [through T-325 days, where T = date of perihelion]
m1 = 11.4 + 5 log d +  5.7 log r [T-325 to T-240 days]
m1 =  7.5 + 5 log d + 12.5 log r [T-240 to T-65 days]
m1 =  8.1 + 5 log d +  8.0 log r [from T-65 days onward]

 

Could this be the best comet of 2021? Perhaps even reaching naked eye brightness (at least for those at a dark site)? As November begins, Leonard is already around magnitude 10.0 as it continues to rapidly brighten as it heads for a close approach to Earth on December 12 at 0.23 au and perihelion on January 3 at 0.62 au. A conservative 2.5n = 8 brightening rate results in Leonard reaching magnitude 6.5 or so by the end of the month. Unfortunately for southern observers, C/2021 A1 is only currently visible from the northern hemisphere as it is located in the northern constellations of Ursa Major (Nov 1-10), Canes Venatici (11-18), Coma Berenices (18-19), Canes Venatici (19-28), Coma Berenices (28-30), and Canes Venatici (30).

 

Catalina Sky Survey astronomer Greg Leonard found C/2021 A1 on 2021 January 3 with the Mount Lemmon 1.5-m reflector when the comet was around magnitude 19 and 5.1 au from the Sun at discovery. Pre-discovery observations from Mount Lemmon and PANSTARRS were found back to April 2020 when the comet was 7.5 au from the Sun. Since then, the comet has alternated between brightening rapidly (through most of 2020), little to no intrinsic brightening (early 2021 through June 2021) and rapidly brightening again (since July 2021). 

 

The conservative 2.5n ~ 8 brightening rate sees Leonard around magnitude 10 at the start of November and magnitude 6.5 at the end of the month. The 2.5n value of 8 results in a peak brightness around magnitude 4.0 when the comet approaches within 0.233 au from Earth on December 12. With a large phase angle reaching 160 degrees at that time, forward scattering of light by cometary dust may increase Leonard’s brightness by an additional 1-2 magnitudes. Working against it are very difficult observing circumstance due to a small solar elongation at the time of maximum brightness (minimum elongation of 15 deg) resulting in the possibility that the comet may be too faint to be seen while so close to the Sun.

 

November provides some nice imaging opportunities for C/2021 A1:
• On Nov 19, it passes ~0.3 deg of the 10th magnitude galaxy NGC 4395.
• Perhaps the PhotoOp of the month will see Leonard travel between the bright galaxies NGC 4631 (the Whale) and 4656 (the Crowbar) on Nov 23/24.
• Looking ahead to next month, Leonard will pass ~0.1 deg of 6th mag globular cluster M3 on Dec 2.

 

8P/Tuttle

 

Discovered on 1790 January 9 by Pierre F. A. Mechain
Rediscovered on 1858 January 5 by Horace Tuttle

 

Orbit (from Minor Planet Center, MPEC 2021-U109)

 

   8P/Tuttle                                                                   
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2021 Aug. 27.73783 TT                                 Rudenko                
q   1.0260059            (2000.0)            P               Q                 
n   0.07228476     Peri.  207.48940     -0.26849547     -0.50829562            
a   5.7073986      Node   270.20397     +0.96326252     -0.13642070            
e   0.8202323      Incl.   54.91128     +0.00595798     -0.85030874            
P  13.6                                                                        
From 253 observations 2008 Feb. 12-2021 Oct. 20, mean residual 0".6.           
     Nongravitational parameters A1 = +0.08, A2 = +0.0579.                     

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

8P/Tuttle                                                        Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  12 29  -40 01   1.408   2.086    35M   Cen   9.8     0   18
2021 Nov 06  12 48  -42 06   1.456   2.134    36M   Cen  10.2     0   18 
2021 Nov 11  13 07  -43 58   1.505   2.184    36M   Cen  10.5     0   18 
2021 Nov 16  13 25  -45 36   1.555   2.234    36M   Cen  10.8     0   19 
2021 Nov 21  13 44  -47 02   1.605   2.284    36M   Cen  11.2     0   19 
2021 Nov 26  14 02  -48 17   1.656   2.333    37M   Cen  11.5     0   19 
2021 Dec 01  14 19  -49 21   1.707   2.381    37M   Cen  11.8     0   19 
2021 Dec 06  14 37  -50 17   1.759   2.427    38M   Cen  12.2     0   20

 

Comet Magnitude Formula

 

m1 = 7.0 + 5 log d + 20 log r(t-25) [Ref: Seiichi Yoshida]

 

8P/Tuttle has been poorly observed this apparition. While the comet peaked at around magnitude 8.5-9.0 in September, it has been poorly placed low in the morning sky. Making matter worse, its placement close to the Sun and deep in the southern sky means it has been unobservable from the northern hemisphere. Only a single observation was sent to the ALPO in October. Chris Wyatt found 8P on October 9th to be magnitude 9.2 (8.6 after correcting for the aperture) with a 2.9’ coma and degree of condensation of 5.

 

November sees Tuttle fade from around magnitude 10 to 12 as it moves through Centaurus (Nov 1-30) and Lupus (Nov 30). Like previous months, it will only be visible to southern hemisphere observers. There are a few nice photo ops for 8P this month: Nov 13/14 - 2.5 deg from bright galaxy Centaurus A, Nov 16/17 - 1.5 deg from bright globular cluster Omega Centauri, and Nov 27 - ~0.3 deg from open cluster NGC 5460.

 

Its best observed apparitions were in 1980/1981 when it reached 6th magnitude and its previous return in 2007/2008 when it passed 0.25 au from Earth and reached 5th magnitude. Two returns from now will be much better when it will pass within 0.18 au of Earth on 2048 December 28 and brighten to 4th magnitude.

 

67P/Churyumov-Gerasimenko

 

Discovered 1969 September 11 by the Klim Ivanovic Churyumov and Svetlana Ivanovna Gerasimenko

 

Orbit (from Minor Planet Center, MPEC 2021-U109)

 

  67P/Churyumov-Gerasimenko                                                    
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2021 Nov. 2.05160 TT                                  Rudenko                
q   1.2106402            (2000.0)            P               Q                 
n   0.15333189     Peri.   22.12208     +0.52361425     -0.85101563            
a   3.4571194      Node    36.33716     +0.77119189     +0.45349743            
e   0.6498124      Incl.    3.87140     +0.36206516     +0.26478762            
P   6.43                                                                       
From 8004 observations 1995 July 3-2021 Oct. 26, mean residual 0".7.           
     Nongravitational parameters A1 = +0.08, A2 = +0.0111.                     

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

67P/Churyumov-Gerasimenko                                         Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  07 19  +26 15   1.210   0.423   110M   Gem   8.7    76   20
2021 Nov 06  07 38  +26 29   1.211   0.421   111M   Gem   8.6    76   20
2021 Nov 11  07 56  +26 37   1.215   0.420   112M   Gem   8.5    77   19
2021 Nov 16  08 12  +26 42   1.223   0.420   114M   Cnc   8.4    77   19
2021 Nov 21  08 25  +26 45   1.233   0.422   116M   Cnc   8.3    77   19
2021 Nov 26  08 37  +26 49   1.247   0.425   118M   Cnc   8.3    77   19
2021 Dec 01  08 47  +26 55   1.263   0.428   121M   Cnc   8.3    77   19
2021 Dec 06  08 54  +27 03   1.283   0.433   124M   Cnc   8.3    77   20

 

Comet Magnitude Formula (modified from Seiichi Yoshida, H value brighter by 0.6 mag) & Lightcurve

 

m1 = 8.9 + 5 log d + 14.0 log r(t-40)

 

67P was discovered on photographic plates taken on 1969 September 11 by Kiev University Astronomical Observatory astronomers Klim Ivanovic Churyumov and Svetlana Ivanovna Gerasimenko working with a 50-cm Maksutov astrograph at the Alma-Ata Astrophysical Institute in current day Kazakhstan. The current apparition is 67P’s 9th observed return with perihelion occurring on 2021 November 2 at 1.21 au. A close approach to Earth at 0.42 au on November 12 makes this the comet’s best return since 1982 when it came marginally closer to Earth at 0.39 au. At that return, a peak brightness of 9th magnitude was reached. 67P was famously the target of the ESA Rosetta/Philae mission, the only spacecraft to have orbited and landed on a comet. This will be 67P’s first return since Rosetta ended its mission by soft landing onto the comet’s surface.

 

As November begins, visual observers are finding 67P to be between magnitude 9.0 and 9.9 (aperture corrected to 8.6 to 9.6). As is seen in images and sketches, 67P also possesses a long tail. Chris Wyatt followed 67P’s tail out to a distance of 11’ in his 0.4-m reflector on October 9 and November 2. While probably too faint for visual observers, imagers such as Michael Jager have also imaged a dust trail in the opposite direction of the dust tail [image]. This feature is visible due to the Earth passing through the comet’s orbital plane in late October.

 

November sees 67P/Churyumov-Gerasimenko remaining well placed for all observers in the late evening through morning sky as it moves through Gemini (Nov 1-12) and Cancer (12-30). The comet should continue to brighten by a few more tenths of a magnitude by the end of the month.

 

C/2019 L3 (ATLAS)

 

Discovered 2019 June 10 by the ATLAS survey with one of their 0.5-m f/2 Schmidt
Dynamically old long-period comet

 

Orbit (from MPEC 2021-U109)

 

    C/2019 L3 (ATLAS)                                                          
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2022 Jan.  9.61968 TT                                 Rudenko                
q   3.5545009            (2000.0)            P               Q                 
z  -0.0004526      Peri.  171.61077     -0.26052266     -0.66630774            
 +/-0.0000003      Node   290.79022     +0.83676024     +0.20517686            
e   1.0016089      Incl.   48.36121     +0.48162252     -0.71689361            
From 2630 observations 2019 June 10-2021 Oct. 27, mean residual 0".4.          

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

C/2019 L3 (ATLAS)                                                 Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  07 47  +40 30   3.611   3.203   106M   Lyn   9.4    89    5
2021 Nov 06  07 47  +40 03   3.603   3.127   110M   Lyn   9.3    90    6
2021 Nov 11  07 47  +39 36   3.596   3.054   115M   Lyn   9.3    89    8
2021 Nov 16  07 46  +39 07   3.589   2.984   120M   Lyn   9.2    89    9
2021 Nov 21  07 45  +38 37   3.583   2.918   125M   Lyn   9.2    89   10
2021 Nov 26  07 43  +38 05   3.577   2.855   130M   Lyn   9.1    88   11
2021 Dec 01  07 40  +37 31   3.573   2.798   135M   Lyn   9.1    87   12
2021 Dec 06  07 37  +36 55   3.568   2.746   141M   Lyn   9.0    87   13

 

Comet Magnitude Formula and Lightcurve (from ALPO and COBS data)

 

m1 =  2.0 + 5 log d + 12.3 log r [through T-550 days; T = date of perihelion]
m1 = -4.6 + 5 log d + 20.8 log r [T-550 to T-150 days]
m1 =  2.8 + 5 log d +  8.0 log r [T-150 days and onwards]

 

C/2019 L3 is still inwards bound to a 2022 January 9 perihelion at a relatively distant 3.57 au. With the comet already being reported to be between magnitude 9.5 and 10.0, the large perihelion distance means C/2019 L3 could remain a visual small telescope object well into 2022. The comet has been brightening at rapid rate since discovery. If we assume a slow down to a more conservative 2.5n = 8 brightening rate till perihelion, it will brighten to around between magnitude 9.0 and 9.5 between November and March.

 

Ten magnitude measurements were submitted to the ALPO since the start of October from J. J. Gonzalez, Christian Harder, Carl Hergenrother, Uwe Pilz, and Chris Wyatt. Reports submitted since the last week of October found C/2019 L3 between magnitude 9.5 and 10.2, aperture corrected to 9.2 to 9.8.

 

C/2019 L3 (ATLAS) spends all month in Lynx (Nov 1-30) in the morning sky. While it has been well placed for northern observers over the past few months, L3 is now moving far enough south to allow southern observations. The comet is in the same part of the sky as comets 4P/Faye and 67P/Churyumov-Gerasimenko. Perhaps because of its proximity to these long-tailed photogenic comets, there hasn’t been as much time spent imaging C/2019 L3. We haven’t received any images or sketches of C/2019 L3 since September.

 

PhotoOps Alerts:
On Nov 16, C/2019 L3 (PANSTARRS) passes within ~0.1 deg of interacting galaxies NGC 2444-2445.
On Nov 24, the comet passes ~1.5 deg from 9th mag globular cluster NGC 2419.

 

Comets Between Magnitude 10 and 13

 

C/2020 T2 (Palomar)

 

Discovered 2020 October 7 at 19th magnitude by the Zwicky Transient Facility (ZTF)
Discovery Telescope: 1.2-m Samuel Oschin Schmidt on Mount Palomar

Dynamically old long-period comet with orbital period of 5560 years

 

Orbit (from MPEC 2021-U109)

 

    C/2020 T2 (Palomar)                                                        
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2021 July 11.14866 TT                                 Rudenko                
q   2.0546861            (2000.0)            P               Q                 
z  +0.0032106      Peri.  150.38351     -0.53886950     +0.70303104            
 +/-0.0000008      Node    83.04814     -0.83514250     -0.37374841            
e   0.9934032      Incl.   27.87302     -0.11025729     -0.60502851            
From 2430 observations 2019 Dec. 11-2021 Oct. 4, mean residual 0".4.           

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

C/2020 T2 (Palomar)                                              Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  17 25  -29 43   2.447   3.059    44E   Oph  11.8     3   23 
2021 Nov 06  17 36  -30 21   2.478   3.128    41E   Sco  11.9     2   21
2021 Nov 11  17 47  -30 56   2.510   3.197    39E   Sco  12.1     1   18
2021 Nov 16  17 58  -31 26   2.543   3.264    36E   Sgr  12.3     0   15
2021 Nov 21  18 10  -31 52   2.577   3.331    34E   Sgr  12.4     0   13
2021 Nov 26  18 21  -32 15   2.611   3.396    31E   Sgr  12.6     0   10
2021 Dec 01  18 32  -32 34   2.646   3.459    29E   Sgr  12.8     0    8
2021 Dec 06  18 43  -32 49   2.682   3.521    27E   Sgr  13.0     0    6

 

Comet Magnitude Formula (from fit to ALPO and COBS data)

 

m1 = 0.6 + 5 log d +24.7 log r(t-34)

 

This is probably the last month to observe C/2020 T2 (PANSTARRS) before it sinks into the glow of twilight. Even then, that’s only for southern observers as the comet is already lost to northern observers. The comet should fade from 12th to 13th magnitude during November as it moves through Ophiuchus (Nov 1-3), Scorpius (3-15), Sagittarius (15-30). By the time C/2020 T2 is once again visible next March, it will be a much fainter object at 15-16th magnitude.

 

4P/Faye

 

Discovered visually on 1843 November 23 by the Herve Faye

 

Orbit (from MPEC 2021-U109)

 

   4P/Faye                                                                     
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2021 Sept. 8.82685 TT                                 Rudenko                
q   1.6188622            (2000.0)            P               Q                 
n   0.13180468     Peri.  206.99424     +0.76786766     -0.63984943            
a   3.8239790      Node   192.93149     +0.61002971     +0.74520437            
e   0.5766550      Incl.    8.00815     +0.19555821     +0.18778486            
P   7.48                                                                       
From 5518 observations 1998 May 24-2021 Oct. 27, mean residual 0".9.           
     Nongravitational parameters A1 = +0.48, A2 = -0.0304.     
   

             

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

4P/Faye                                                           Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  06 46  +11 35   1.705   1.016   116M   Mon  10.4    61   37
2021 Nov 06  06 50  +10 49   1.722   0.997   119M   Mon  10.4    61   38
2021 Nov 11  06 53  +10 06   1.739   0.980   123M   Mon  10.5    60   39
2021 Nov 16  06 55  +09 25   1.758   0.965   128M   Mon  10.5    59   40
2021 Nov 21  06 56  +08 48   1.778   0.953   132M   Mon  10.6    59   41
2021 Nov 26  06 55  +08 16   1.798   0.944   137M   Mon  10.7    58   42
2021 Dec 01  06 54  +07 49   1.820   0.938   142M   Mon  10.8    58   42
2021 Dec 06  06 51  +07 28   1.843   0.937   146M   Mon  10.9    57   43

 

Comet Magnitude Formula (from fit to ALPO and COBS data)

 

m1 = 5.4 + 5 log d + 21.3 log r

 

4P/Faye was a visual discovery by Herve Faye (Royal Observatory, Paris, France) on 1843 November 23. The comet was abnormally bright and reported to be visible to the naked eye only days after discovery. At its best subsequent apparitions, it only peaked at 9th magnitude (as in 1991 and 2006).

 

This year’s apparition is Faye’s 22nd observed return with the comet having been missed at its 1903 and 1918 returns. 2021 is a moderately good, but not great, apparition with perihelion on 2021 September 8 at 1.62 au. Even though perihelion was a month ago, the comet will continue to move closer to the Earth until December 5 (0.94 au). As a result, it will stay close to maximum brightness through November. It is a morning object observable from both hemispheres as its moves through Monoceros.

 

Faye was well observed in October with no less than a dozen visual observations submitted to the ALPO. The most recent observations from November 5th placed the comet around magnitude 10.6-11.2 (aperture corrected to 10.2 to 10.9). While the tail has been a striking feature in images, visual observers have also caught glimpses of the tail. Chris Wyatt reported a 7.5’ long tail with a 0.4-m reflector on October 9.

 

6P/d’Arrest

 

Discovered on 1851 June 28 by the Heinrich Ludwig d'Arrest

 

Orbit (from MPEC 2021-U109)

 

   6P/d'Arrest                                                                 
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2021 Sept. 17.78506 TT                                Rudenko                
q   1.3545948            (2000.0)            P               Q                 
n   0.15067526     Peri.  178.10556     +0.73308836     +0.64376842            
a   3.4976371      Node   138.93541     -0.62832017     +0.76453460            
e   0.6127115      Incl.   19.51257     -0.26037516     -0.03238932            
P   6.54                                                                       
From 3114 observations 1987 Mar. 31-2021 Oct. 26, mean residual 1".0.          
     Nongravitational parameters A1 = +0.53, A2 = +0.0991.       

              

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

6P/d'Arrest                                                       Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  20 44  -31 46   1.446   1.112    86E   Mic  10.2    18   62
2021 Nov 06  21 03  -31 31   1.467   1.157    85E   Mic  10.2    18   60
2021 Nov 11  21 22  -31 03   1.489   1.206    84E   Mic  10.3    19   58
2021 Nov 16  21 40  -30 24   1.513   1.256    83E   PsA  10.4    20   56
2021 Nov 21  21 57  -29 35   1.538   1.309    82E   PsA  10.5    20   53
2021 Nov 26  22 14  -28 37   1.565   1.365    81E   PsA  10.6    21   51
2021 Dec 01  22 30  -27 33   1.593   1.423    80E   PsA  10.7    22   48
2021 Dec 06  22 45  -26 23   1.622   1.483    79E   PsA  10.9    24   45

 

Comet Magnitude Formula (from fit to ALPO and COBS data, seasonal offset fixed at T+60 days)

 

m1 = 6.6 + 5 log d + 24.8 log r(t-60)

 

Heinrich Louis d’Arrest discovered 6P visually in June 1851. We now know that it had also been observed by Phillipe la Hire in 1678. Long-time comet watchers may remember this comet’s excellent apparition in 1976 when it passed 0.15 au from Earth and reached 5th magnitude. d’Arrest’s perihelion distance is larger now (1.35 au) so such close approaches are no longer possible. This year, closest approach to Earth was on August 2 at 0.75 au and perihelion on September 17.

 

d’Arrest usually possesses an asymmetrical lightcurve with respect to perihelion. In d’Arrest’s case, it means the comet is at its brightest nearly a month after perihelion. If this is true this return, it should fade this month after peaking in brightness at around magnitude 10.2. In late October we received magnitude estimates from Chris Wyatt, original mag 10.6, aperture corrected mag 10.2, on the 25th and J. J. Gonzalez, original mag 10.2, aperture corrected mag on 9.9, on the 27th. Both observers measured a coma on the order of 4-5’.

 

d’Arrest remains an evening object as it moves through Microscopium (Nov 1-11), Pisces Austrinus (Nov 11-30).

 

19P/Borrelly

 

Discovered 1904 December 28 by the Alphonse Borrelly
Short-period comet with orbital period of ~6.85 years

 

Orbit (from Minor Planet Center, MPEC 2021-U109)

 

  19P/Borrelly                                                                 
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2022 Feb. 1.80438 TT                                  Rudenko                
q   1.3063303            (2000.0)            P               Q                 
n   0.14391022     Peri.  351.89099     +0.38690377     -0.79268559            
a   3.6064089      Node    74.26303     +0.87111749     +0.14663878            
e   0.6377753      Incl.   29.30561     +0.30242319     +0.59173188            
P   6.85                                                                       
From 419 observations 2015 Jan. 11-2021 Oct. 25, mean residual 0".7.           

     Nongravitational parameters A1 = -0.73, A2 = -0.5606.                     

 

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

19P/Borrelly                                                     Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  23 04  -52 04   1.689   1.193   100E   Gru  11.6     0   78
2021 Nov 06  23 05  -50 11   1.655   1.189    98E   Gru  11.3     0   79
2021 Nov 11  23 07  -48 06   1.622   1.186    95E   Gru  11.1     2   78
2021 Nov 16  23 11  -45 50   1.590   1.183    93E   Gru  10.9     4   76
2021 Nov 21  23 15  -43 25   1.559   1.180    91E   Gru  10.7     7   72
2021 Nov 26  23 20  -40 50   1.529   1.177    89E   Gru  10.5     9   67
2021 Dec 01  23 26  -38 07   1.500   1.175    87E   Gru  10.3    12   63
2021 Dec 06  23 33  -35 14   1.473   1.174    85E   Scl  10.1    15   58

 

Comet Magnitude Formula (from Seiichi Yoshida)

 

m1 = 5.5 + 5 log d + 25.0 log r

 

19P/Borrelly will be one of the better comets of 2022 when it should reach 9th magnitude around the time of its 2022 February 1 perihelion (at 1.31 au). Till now, the comet has only been observable from the southern hemisphere. Chris Wyatt was able to observe it from his home in Australia on 4 nights in October. His last observation on October 25th found 19P to be magnitude 12.9 (aperture corrected to 12.3) with a moderately condensed 1.2’ coma. By mid-month, northern observers will be able to visually observe Borrelly as it moves northward through Grus in the evening sky. It should reach a brightness around magnitude 10.5 by the end of November.

 

19P/Borrelly is one of 10 comets and 18 Main Belt asteroids discovered by Alphonse Borrelly from the Marseille Observatory. In addition to his discovery of 19P in 1904, Borrelly also discovered C/1873 Q1 (Borrelly), C/1874 O1 (Borrelly), C/1874 X1 (Borrelly), C/1877 C1 (Borrelly), C/1889 X1 (Borrelly), C/1900 O1 (Borrelly-Brooks), C/1903 M1 (Borrelly), C/1909 L1 (Borrelly-Daniel), C/1912 V1 (Borrelly).

 

The current apparition marks the comet’s 16th observed return. 19P’s orbit has been stable since discovery with perihelion staying between 1.30 and 1.46 au (this year it is at 1.31 au so nearly as close as it’s been since discovery). The comet approached within 1 au of Earth during its first 4 observed returns (1904, 1911, 1918 and 1925) and peaked between 8th and 10th magnitude. There was a stretch of 6 perihelion passages between 1938 and 1974 when the comet arrived at perihelion almost directly behind the Sun at ~2.3 to 2.5 au from Earth. Returns in 1987 and 1994 were much better with approaches to 0.48 and 0.62 au of Earth and peaks at magnitude 7 and 7.5, respectively. 2022 starts a new cycle of good apparitions. Though still a distant 1.18 au from Earth at its closest this time around, it will come closer in 2028 (0.41 au) and 2035 (0.62 au). The 2028 will be Borrelly’s best observed return.

 

29P/Schwassmann-Wachmann

 

Discovered 1927 November 15 by the Arnold Schwassmann and Arno Arthur Wachmann at the Hamburg Observatory in Bergedorf, Germany
Centaur comet with orbital period of ~14.8 years

 

Orbit (from Minor Planet Center, MPEC 2021-U109)

 

  29P/Schwassmann-Wachmann                                                     
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2019 Mar. 26.65803 TT                                 Rudenko                
q   5.7691442            (2000.0)            P               Q                 
n   0.06642076     Peri.   49.15092     +0.99219432     -0.03308064            
a   6.0385613      Node   312.37551     -0.03076826     +0.86941941            
e   0.0446161      Incl.    9.36679     +0.12084592     +0.49296608            
P  14.8                                                                        
From 9993 observations 2018 June 18-2021 Aug. 10, mean residual 0".6.          

                                                                               
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

29P/Schwassmann-Wachmann                                         Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  04 52  +32 16   5.927   5.113   141M   Aur   var    82   18
2021 Nov 06  04 50  +32 16   5.928   5.071   147M   Aur   var    82   18
2021 Nov 11  04 48  +32 15   5.930   5.035   152M   Aur   var    82   18
2021 Nov 16  04 45  +32 13   5.931   5.006   157M   Aur   var    82   18
2021 Nov 21  04 43  +32 10   5.932   4.984   162M   Aur   var    82   18
2021 Nov 26  04 40  +32 05   5.934   4.970   166M   Aur   var    82   18
2021 Dec 01  04 37  +31 59   5.935   4.963   169M   Per   var    82   18
2021 Dec 06  04 35  +31 52   5.937   4.964   170E   Per   var    82   18

 

29P/Schwassmann-Wachmann was discovered photographically on 1927 November 15 by German observing team Arnold Schwassmann and Arno Arthur Wachmann. The duo discovered 4 comets together, three short-period comets (29P/Schwassmann-Wachmann, 31P/Schwassmann-Wachmann, and 73P/Schwassmann-Wachmann) and a long-period comet shared with Leslie Peltier [C/1930 D1 (Peltier-Schwassmann-Wachmann)].

 

29P is one of the more enigmatic comets. It is always active and rarely fainter than 17th-18th magnitude. Multiple times per year outbursts occur resulting in a peak brightness that can reach 10th magnitude though most peaks fall in the 11th to 14th magnitude range. This is especially odd since the comet’s orbit is nearly circular (e=0.04), so the comet does not experience large variations in solar heating like most comets. Richard Miles (Director of the British Astronomical Society’s Asteroids and Remote Planets Section) has published a series of papers on 29P and its outbursts. He found that as many as 6 active areas are producing outbursts on a nucleus with a rotation period of ~57-58 days.

 

29P is also considered a member of the Centaur population. Different organizations have different definitions for what constitutes a member of the Centaurs. The two most common definitions are from the Minor Planet Center (perihelion beyond the orbit of Jupiter and semi-major axis within the orbit of Neptune) and the Jet Propulsion Laboratory (semi-major axis between the orbits of Jupiter and Neptune). Both definitions would classify 29P as a Centaur.

 

Currently the comet is in the midst of a series of major outbursts. Outbursts were observed on September 25, 26, two on 27, October 16, 23, and November 3. As a result, the comet is about as bright as it ever gets with many visual observers reporting the comet to be between magnitude 10 and 11 with a coma diameter between 1.2’ and 4’. Imagers and some visual sketchers are reporting jet-like features in the inner coma.

 

The comet is approaching opposition this month in Auriga and observable from both hemispheres. If you observe 29P, please consider contributing to two pro-am efforts to better understand this object: the British Astronomical Society’s (BAA) Mission 29P monitoring program coordinated by Richard Miles. ( https://britastro.org/node/18562 & https://britastro.org/node/25120 ) and the University of Maryland’s 29P Observation campaign (https://wirtanen.astro.umd.edu/29P/29P_obs.shtml).

 

57P/du Toit-Neujmin-Delporte

 

Discovered on 1941 July 18 by Daniel du Toit at the Harvard College Observatory’s Boyden Station in South Africa, on 1941 July 25 by Grigory N. Neujmin at the Simeis Observatory in Russia, and on 1941 August 19 by Eugéne Joseph Delporte of the Royal Observatory in Uccle, Belgium
Jupiter-family comet with orbital period of 6.4 years

 

Orbit (from Minor Planet Center, MPEC 2021-U109)

 

  57P/du Toit-Neujmin-Delporte                                                 
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2021 Oct. 17.42636 TT                                 Rudenko                
q   1.7201104            (2000.0)            P               Q                 
n   0.15406554     Peri.  115.26138     +0.55958663     +0.82873711            
a   3.4461357      Node   188.77764     -0.77715503     +0.52153147            
e   0.5008582      Incl.    2.85093     -0.28791121     +0.20297715            
P   6.40                                                                       
From 1000 observations 2015 Feb. 18-2021 Oct. 26, mean residual 0".6.          

                                                                               
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

57P/du Toit-Neujmin-Delporte                                     Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  18 47  -20 51   1.726   1.940    62E   Sgr   var    21   34
2021 Nov 06  19 02  -20 39   1.730   1.979    60E   Sgr   var    21   31
2021 Nov 11  19 16  -20 21   1.735   2.019    59E   Sgr   var    21   28
2021 Nov 16  19 30  -19 59   1.742   2.059    57E   Sgr   var    21   25
2021 Nov 21  19 44  -19 32   1.750   2.101    55E   Sgr   var    21   22
2021 Nov 26  19 58  -19 00   1.759   2.143    54E   Sgr   var    21   19
2021 Dec 01  20 12  -18 24   1.769   2.187    52E   Cap   var    21   17
2021 Dec 06  20 26  -17 44   1.780   2.231    50E   Cap   var    21   14

 

Discovered in 1941, 57P/du Toit-Neujmin-Delporte is making its 9th observed return and was not expected to become much brighter than 16th magnitude. That was the case until October 17, its perihelion date, when comet imager Francois Kugel captured the comet at magnitude 11.9 [image].

 

Daniel du Toit was the first person to discover 57P on 1941 July 18 from the Harvard College Observatory’s Boyden Station in South Africa only a few days after a close approach to Earth of 0.30 au. Due to World War II, communications were slow and two other observers, Grigory N. Neujmin at Simeis Observatory in Russia and Eugéne Joseph Delporte of the Royal Observatory in Uccle, Belgium also found the comet over the next month or so. All three observers reported the comet to be around 9-10th magnitude. For du Toit, 57P was one of five discoveries including 66P/du Toit, 79P/du Toit-Hartley, C/1945 L1 (du Toit), and the sungrazer C/1945 X1 (du Toit). Neujmin found six comets including 25D/Neujmin, 28P/Neujmin, 42P/Neujmin, 58P/Jackson-Neujmin, and C/1914 M1 (Neujmin). 57P is the only discovery by Delporte.

 

At its discovery apparition in 1941, 57P had a perihelion distance of 1.31 au. A close approach to Jupiter in 1954 of 0.69 au moved its perihelion out to around 1.48 au. Another Jupiter approach in 1966 of 0.64 au moved perihelion out once again this time to around 1.67 au. Since then, its perihelion has marginally increased to the current value of 1.72 au. The comet’s increasing perihelion distance, the possibility that it was in outburst and abnormally bright in 1941, and in some cases poor placement led to missed returns in 1947, 1952, 1958, and 1964. The 1964 return, while not as good as the 1941 return, did see 57P come within 0.50 au of Earth but due to presumed faintness was not seen.

 

Brian Marsden (Minor Planet Center) was able to accurately predict the comet’s 1970 return allowing a photographic recovery by Charles Kowal at 19th magnitude [IAUC 2222,2264]. 1977 would be another missed apparition but the comet would be observed at every subsequent return starting in 1983.

 

The abnormal brightness in 1941 was suggestive of an outburst. The comet’s behavior in 1996 confirmed that 57P was indeed outburst prone when it brightened by ~6 magnitude to 12th magnitude 3-4 months after perihelion [IAUC 6441]. The 2002 return saw the comet accompanied by 19 secondary nuclei [IAUC 7934,7935], the result of a series of splitting events that could have started during the previous return in 1996 [IAUC 7946,7957].

 

At the end of October, visual observers J. J. Gonzalez, Christian Harder, and Chris Wyatt observed 57P to be between magnitude 11.3 and 12.7 (corrected to 10.8 to 12.1) with a coma diameter between 0.9 and 2.0’. Wyatt also noted a 2.6’ long tail. November sees 57P as an evening object in Sagittarius (Nov 1-29) and Capricornus (29-30). Unless another outburst occurs, 57P should rapidly fade over the coming weeks.

 

C/2017 K2 (PANSTARRS)

 

Discovered 2017 May 21 by the Pan-STARRS survey with the Pan-STARRS1 1.8-m on Haleakala
Dynamically old long-period comet

 

Orbit (from MPEC 2021-U109)

 

    C/2017 K2 (PANSTARRS)                                                      
Epoch 2022 Dec. 7.0 TT = JDT 2459920.5                                         
T 2022 Dec. 19.67922 TT                                 Rudenko                
q   1.7969357            (2000.0)            P               Q                 
z  -0.0004685      Peri.  236.19780     +0.01818629     +0.04922985            
 +/-0.0000003      Node    88.23555     -0.18093746     +0.98245825            
e   1.0008419      Incl.   87.56304     -0.98332644     -0.17986721            
From 6796 observations 2013 May 12-2021 Oct. 26, mean residual 0".5. 

          

Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

C/2017 K2 (PANSTARRS)                                             Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  17 13  +20 41   4.934   5.448    54E   Her  11.8    37    0
2021 Nov 06  17 16  +19 52   4.891   5.443    51E   Her  11.8    34    0
2021 Nov 11  17 19  +19 05   4.847   5.435    49E   Her  11.8    31    0
2021 Nov 16  17 23  +18 20   4.803   5.423    46E   Her  11.7    28    0
2021 Nov 21  17 26  +17 38   4.759   5.408    44E   Her  11.7    25    0
2021 Nov 26  17 30  +16 58   4.715   5.389    42E   Her  11.6    22    0
2021 Dec 01  17 33  +16 20   4.671   5.366    41E   Her  11.6    19    0
2021 Dec 06  17 37  +15 44   4.627   5.339    39E   Her  11.6    16    0

 

Comet Magnitude Formula (from ALPO and COBS data)

 

m1 =  2.6 + 5 log d + 8.0 log r

 

C/2017 K2 (PANSTARRS) was discovered on 2017 May 21 by the Pan-STARRS1 1.8-m telescope at Haleakala on the Hawaiian island of Maui. At discovery the comet was around 21st magnitude and located at 16.1 au from the Sun. Pre-discovery observations were found back to May of 2013 when the comet was 23.7 au from the Sun which is further than the distance of Uranus. Even though it was discovered over 2.5 years ago, perihelion is still over a year away on 2022 December 19 at 1.80 au.

 

Multiple visual observations were submitted in October by J. J. Gonzalez, Christian Harder, Uwe Pilz, and Chris Wyatt. The visual magnitudes ranged between 10.4 and 12.7 with coma diameters between 1’ and 3’. The comet seems to be following a steady brightening rate of 2.5n ~ 8 going back to 2017. The prediction above shows the comet brightening from around magnitude 11.8 to 11.6 this month. Note, that since the comet has brightened into visual range, a few observers have routinely estimated the comet to be a magnitude or more brighter than the prediction. It will be interesting if more observers using smaller apertures start picking up the comet in the coming weeks at a brighter magnitude than predicted.

 

C/2017 K2 is an evening object in Hercules and only visible from the northern hemisphere. Though closing in on solar conjunction, the comet will pass far enough north of the Sun to be followed through conjunction. Southern hemisphere observers won’t see the comet again till February 2022 when it should be magnitude 10.5. Northern observers will be able to follow the comet continuously till late September when it will travel too far south (around magnitude 7.0 at that time). C/2017 K2 should peak in January 2023 around magnitude 6.5 and at a far southern declination of -70 deg. Northern observers will see the comet again till August 2023 when it will have faded to around magnitude 10.0.

 

Fainter Comets of Interest (Fainter than 13.0)

 

C/2021 O3 (PANSTARRS)

 

Discovered 2021 July 26 by Pan-STARRS with the 1.8-m Pan-STARRS1 1.8-m on Haleakala

 

Orbit (from Minor Planet Center, MPEC 2021-U109)

 

    C/2021 O3 (PANSTARRS)                                                      
Epoch 2021 July 5.0 TT = JDT 2459400.5                                         
T 2022 Apr. 21.05266 TT                                 Rudenko                
q   0.2872445            (2000.0)            P               Q                 
z  -0.0004002      Peri.  299.97411     -0.56820943     -0.81228783            
 +/-0.0000104      Node   189.05865     +0.64653726     -0.53964602            
e   1.0001150      Incl.   56.72398     -0.50904579     +0.22129314            
From 458 observations 2021 July 26-Oct. 26, mean residual 0".4.                

                                                                               
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)

 

C/2021 O3 (PANSTARRS)                                             Max El
                                                                  (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021 Nov 01  22 00  +14 49   3.132   2.565   116E   Peg  17.5    65   33
2021 Nov 06  21 58  +13 33   3.066   2.568   110E   Peg  17.4    64   33
2021 Nov 11  21 56  +12 19   2.999   2.574   105E   Peg  17.4    62   31
2021 Nov 16  21 55  +11 07   2.932   2.583   100E   Peg  17.3    61   28
2021 Nov 21  21 55  +09 59   2.865   2.594    95E   Peg  17.2    60   25
2021 Nov 26  21 55  +08 55   2.796   2.605    90E   Peg  17.2    58   22
2021 Dec 01  21 57  +07 54   2.727   2.617    85E   Peg  17.1    56   19
2021 Dec 06  21 58  +06 58   2.657   2.628    80E   Peg  17.0    54   15

 

Comet Magnitude Formula (based on data submitted to the COBS and the MPC)

 

m1 = 11.5 + 5 log d + 8 log r

 

C/2021 O3 (PANSTARRS) was first seen on July 26 at 19th magnitude by the Pan-STARRS1 1.8-m Ritchey-Chretien on Haleakala. Perihelion will occur on 2022 April 21 at a close distance of 0.29 au from the Sun. C/2021 O3 will experience some of the same observational issues as C/2021 A1 (Leonard). On the plus side, PANSTARRS will reach a relatively large phase angle though not as large as Leonard (only ~136 vs 160 deg). But PANSTARRS will also be located at very small solar elongations near perihelion which will make it a VERY difficult object to observe until a few weeks after perihelion and then only for northern observers. Not helping matters is C/2020 O3’s faintness.

 

Since discovery, C/2021 O3 has been brightening very slowly and remains a 17th magnitude object. While there is still hope it could become a nice small aperture object next April and May, the slow rate of brightening is a cause for concern. Its intrinsic faintness and small perihelion distance suggest an object that may not survive perihelion or even reach perihelion. Then again, the comet is a dynamically old long-period comet with a ~7200-year period so it has survived at least one, and possible multiple, perihelion passage(s).

 

November sees C/2021 O3 as an evening object in Pegasus in the evening sky for observers in both hemispheres. Southern hemisphere observers should be able to follow PANSTARRS till the end of the year when the comet could be around 15-16th magnitude. Northern hemisphere observers will be able to follow it for another month or two till mid-February when it could be as bright as 13-14th magnitude. The comet will then spend the next two and a half months within 20 deg of the Sun.

 

The following paragraph hasn’t changed from last month’s issue:

The comet’s orbit is aligned in such a way that the comet will be mainly a northern hemisphere object except for a week or so centered on perihelion. On the date of perihelion C/2021 O3 will be an evening object located only 16 deg from the Sun. Northern hemisphere observers (for +40N) will not be able to observe it at that time as it will still be 7 deg below the horizon at the start of nautical twilight. It will be observable from the southern hemisphere (-40S) when it will be at an elevation of 5 deg at the start of nautical twilight and only 1 deg below the horizon at the start of astronomical twilight. If its rate of brightening is 2.5n ~ 8, it will be at 6-7th magnitude. The combination of faintness and poor placement near the Sun will make observing this comet very difficult. The comet becomes observable in a dark sky (after the end of astronomical twilight) by the first few nights of May. This is around the time of maximum phase angle (135 deg) which may provide a 1-2 magnitude boost in brightness. Still, we are talking about an object that may only be around 4th-6th magnitude and still located ~20 deg from the Sun. Though it will be fading fast, the comet will quickly move north and become circumpolar by mid-May. Note, that this all assumes this apparently intrinsically faint comet survives its close brush with the Sun. Time will tell.

 

New Discoveries, Recoveries and Other Comets News

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.

 

C/2021 U4 (Leonard) – The 13th comet to be discovered by Greg Leonard of the Catalina Sky Survey was found on October 31 at 19th magnitude with the Mt Lemmon 1.5-m. C/2021 U4 appears to have a >300-year orbital period. Perihelion is next month on December 21 at 1.79 au meaning the comet is not likely to get much brighter. [CBET 5065, MPEC 2021-V22]

 

P/2021 U3 (Attard-Maury) – The MAP project team of Alain Maury, Georges Attard, and Daniel Parrott have found their 2nd comet, the first being C/2021 J1 (Maury-Attard). Alain was also the discoverer of comets C/1988 C1 (Maury-Phinney), 115P/1985 Q1 (Maury), and 198P/1998 X1 (ODAS). P/2021 U3 was found on October 24 at 19th magnitude with a 0.4-m reflector at San Pedro de Atacama in Chile. The comet has an 8.7-year period and perihelion on 2021 October 25 at 1.89 au. It should brighten to 17th magnitude when it arrives at opposition this December. [CBET 5064, MPEC 2021-V21]

 

P/2021 U1 (Wierzchos) - Kacper W. Wierzchos discovered a new 19th magnitude short-period comet on October 18 with the Mount Lemmon 1.5-m. This is the 3rd comet to carry Kacper’s name and second from this year. Perihelion occurred back on 2021 September 30 at 2.45 au so the comet is likely passed maximum brightness. It will return in ~25 years. [CBET 5058, MPEC 2021-U43]

 

C/2021 T4 (Lemmon) – An apparently asteroidal object was found with the Mt Lemmon 1.5-m on October 7 at 20th magnitude. Pre-discovery observations from Mount Lemmon and Pan-STARRS was found back to August. With a perihelion not till 2023 July 31 at 1.48 au, C/2021 T4 should have plenty of time to brighten into a nice small aperture object. A conservative 2.5n = 8 brightening rate results in a peak brightness around magnitude 9.0 in late July 2023. Not only will the comet be at perihelion at that time but also at its closest approach to Earth at 0.54 au. Unfortunately for northern observers, the comet will be located far to the south (up to a declination of -56 deg) at its best. The comet starts November ~7 au from the Sun so we have plenty of time to watch this one develop.

 

P/2021 T3 = P/2015 K6 (PANSTARRS) – A new 20th magnitude short-period comet was found with the Pan-STARRS1 1.8-m on October 2. Additional pre-discovery images were found at its previous return in 2015-2017 in DECam (on the Cerro Tololo 4-m) and Pan-STARRS data. A single night observation was also found in 2002 in Sloan Digital Sky Survey data. Perihelion was this summer on 2021 July 27 at 2.06 au. The comet will be back again in 5.25 years with its next perihelion on 2026 October 26. [CBET 5056, MPEC 2021-T184]

 

C/2021 T2 (Fuls) – D. Carson Fuls discovered the 6th comet to bear his name on October 2 at 20th magnitude with the Mt Lemmon 1.5-m. Currently around 3 au from the Sun, C/2021 T2 will be much closer on 2022 June 7 when it arrives at perihelion at 1.25 au from the Sun. At that time, the comet will be around 13-14th magnitude but only visible to southern hemisphere observers. [CBET 5054, MPEC 2021-T169]

C/2021 T1 (Lemmon) – An apparently asteroidal object was discovered at 19-20th magnitude with the Mount Lemmon 1.5-m on October 2. C/2021 T1 is just passed its October 14 perihelion at 3.06 au. The comet has likely already peaked in brightness. [CBET 5053, MPEC 2021-168]

 

C/2021 S4 (Tsuchinshan) - Hai-bin Zhao reported the discovery of a 19th magnitude comet on images taken on September 29 with the 1.04-m f/1.8 Schmidt telescope at the XuYi station of the Purple Mountain (Tsuchinshan) Observatory.At discovery, the object was reported as asteroidal. This is the 5th comet to be named after Tsuchinshan Observatory. C/2021 S4 is a high-q long-period comet with a period of ~2700 years. Perihelion isn’t till 2023 December 25 at 6.78 au. It should peak at around magnitude 18-19. [CBET 5052, MPEC 2021-T167]

 

C/2021 S3 (PANSTARRS) –The Pan-STARRS2 1.8-m was used to discover this comet at 19th magnitude on September 24. C/2021 S3 has a chance of becoming a nice 8th magnitude object when it arrives at perihelion though that won’t be till early 2024 when it reaches perihelion (1.33 au on 2024 February 19) and closest approach to Earth (1.23 au on 2024 March 18). The comet’s orbit suggests that it is a dynamically old long-period comet. Like C/2021 T4 (Lemmon), we’ve got time to watch this one develop as we await perihelion. As November starts, the comet is located 8.6 au from the Sun. Unlike C/2021 T4, C/2021 S3 will be well place for observation from both hemispheres in the morning sky.

 

C/2021 R7 (PANSTARRS) – Both Pan-STARRS 1.8-m telescopes were involved in the discovery of this comet on the night of September 5. C/2021 R7 is a faint distant comet that should not get any brighter than its current brightness (21st mag). Perihelion was back on 2021 April 16 at 5.65 au.

 

C/2021 G2 (ATLAS) - An apparently asteroidal object was discovered on 2021 April 11 at 19th magnitude with the ATLAS 0.5-m f/2 astrograph on Mauna Loa. Pre-discovery observations have been found back to November 2020. C. Holt, University of Maryland, and M. Micheli found evidence of cometary activity in images taken on September 29 with the 4.1-m SOAR telescope at Cerro Pachon in Chile. This confirms reports of activity by other observers published in CBET 4988. The object is currently 9.0 au from Sun and nearly 3 years from a 2024 September 9 perihelion at 4.98 au. A peak brightness around 14th magnitude is expected in 2024. [Discovery Ref: MPEC 2021-M79, CBET 4988; New Activity ref: CBET 5057]

As always, the Comet Section is happy to receive all comet observations, whether textual descriptions, images, drawings, magnitude estimates, or spectra. Please send your observations via email to the Comets Section < comets @ alpo-astronomy .org >, Comets Section Coordinator Carl Hergenrother < carl.hergenrother @ alpo-astronomy .org > and/or Comets Section Acting Assistant Coordinator Michel Deconinck < michel.deconinck @ alpo-astronomy .org >.

 

Thank you to everyone who contributed to the ALPO Comets Section!

 

Stay safe and enjoy the sky!
- Carl Hergenrother


  • Artom, waso29, SNH and 2 others like this

#2 Octans

Octans

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Posted 07 November 2021 - 02:18 PM

Latest orbital solution from the Minor Planet Center (which is in agreement with JPL) shows that C/2021 O3 has an inbound barycentric z=1/a=0.000053 +/- 0.000010 au^-1, corresponding to a very large a=19000 +/- 3000 au (~3 million year orbital period). The error bars are likely too small due to potential systematic offsets in astrometry, but the orbit looks far more likely to be dynamically new than old at this point.



#3 Carl H.

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Posted 07 November 2021 - 09:11 PM

Latest orbital solution from the Minor Planet Center (which is in agreement with JPL) shows that C/2021 O3 has an inbound barycentric z=1/a=0.000053 +/- 0.000010 au^-1, corresponding to a very large a=19000 +/- 3000 au (~3 million year orbital period). The error bars are likely too small due to potential systematic offsets in astrometry, but the orbit looks far more likely to be dynamically new than old at this point.

You are correct. I mistakenly attributed the inbound 1/a of C/2021 S3 (PANSTARRS) to C/2021 O3 (PANSTARRS). I agree C/2021 O3 does appear to more likely be a dynamically new comet which unfortunately does not bode well for its future development. On the other hand, maybe we'll get to watch another comet disintegrate in a few months.

 

Thanks for pointing out the error.


Edited by Carl H., 07 November 2021 - 09:41 PM.


#4 emh52

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Posted 16 November 2021 - 04:01 PM

This is Atlas in conjunction with Arp 143 (NGC 2444 and 2445) as outlined in Carl's report, with a nearby spiral nearly at the nucleus. Captured with T19 iTelescope- the imaging window was only about 45 min just before dawn, Better resolution https://flic.kr/p/2mKdfZo

Attached Thumbnails

  • CN Atlas and ARP143 .jpg

Edited by emh52, 16 November 2021 - 04:02 PM.



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