21 replies to this topic

[Carl H.]

ALPO COMET NEWS FOR JANUARY 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 magnitude estimates and figures). 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.

 

While many of us are happy to see the end of 2020, it was actually quite a good year for comet observing. No less than 13 comets were observed at magnitude 10.0 or brighter. The comet highlight of the year was C/2020 F3 (NEOWISE) which was the most impressive comet for northern hemisphere observers since C/1995 O1 (Hale-Bopp) in 1997.

 

Though it is unlikely 2021 will deliver another NEOWISE-like event, the year is predicted to see a large number of reasonably bright short-period comets, though most won’t be bright till the 2nd half of the year. As a result, 2021 will start off slow with no comets expected to be brighter than 10th magnitude in January. We may need to wait till February or March when long-period comet C/2020 R4 (ATLAS) could become bright enough for small aperture observers.

 

Bright Comets (magnitude < 10.0)

 

None.

 

Fainter Comets of Interest (generally fainter than magnitude 10.0)


 

C/2020 S3 (Erasmus) – Barring a surprise discovery or major outburst, no comet observable from Earth is expected to be brighter than 10th magnitude this month. C/2020 S3 (Erasmus), on the other hand, is visible within the FOV of the LASCO C3 coronagraph on the SOHO spacecraft. Though, even this is a stretch for January 2021 as it expected to leave the C3 FOV on January 1 or 2, perhaps even before you read this.

 

Comet C/2020 S3 (Erasmus) is a dynamically old long-period comet with an orbital period on the order of ~2600 years and was a faint 17th magnitude object at discovery back on 2020 September 17 with the ATLAS 0.5-m f/2 Schmidt at Mauna Loa. The comet rapidly brightened in November before being lost in the glare of dawn in early December. Willian Souza followed Erasmus down to an elongation of 23 degrees on December 4.30 UT when he estimated it at magnitude 6.1.

 

The comet was next imaged during the December 14 Total Solar Eclipse (see Nick James’ image at the BAA Comet Section Image Archive which also shows C/2020 X3) when it was located only 11 degrees from the Sun. Four days later, Erasmus entered the SOHO LASCO C3 FOV. Mieczyslaw Leszek Paradowski submitted magnitude measurements to the COBS website showing Erasmus at magnitude 3.9 on December 18.58 UT as it entered the C3 FOV. By December 31.44 UT, it was measured to have faded to magnitude 6.1. If these magnitudes are accurate, Erasmus must have either rapidly brightened or experienced an outburst since early December. The quick fade from magnitude 3.9 to 6.1 in the C3 data also suggests a possible outburst may have occurred.

 

Unfortunately, once Erasmus leave the C3 FOV in a day or two, we may not see it again till April when it will finally be observable from Earth though as an object too faint for visual observation.

 

C/2020 M3 (ATLAS) – C/2020 M3 (ATLAS) is a Halley-type comet with an orbital period of 139 years. Perihelion occurred on October 25 at 1.27 au and closest approach to Earth on November 14 at 0.36 au. ATLAS held steady near its peak brightness (magnitude 7.5 to 8.0) for most of November. As it moved away from the Earth and Sun in December, ATLAS started to rapidly fade and was estimated between magnitude 9.4 and 9.7 by J. J. Gonzalez and Chris Wyatt on December 8, 9, and 16. Both observers observed a diffuse 5-6’ coma.

 

As 2021 begins, C/2020 M3 is well placed for northern observers in the evening sky in Auriga. If its rapid fading continues, it may be lost to most visual observers by the end of the month as it drops below 12-13th magnitude.

 

C/2020 M3 (ATLAS)
T = 2020-Oct-25  q = 1.27 au                                      Max El
Halley-family comet – 139-year orbital period                      (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021-Jan-01  05 14  +45 28   1.603   0.672   150E   Aur  10.7    84    4
2021-Jan-06  05 15  +46 39   1.647   0.733   146E   Aur  11.1    83    3
2021-Jan-11  05 16  +47 30   1.692   0.799   142E   Aur  11.5    82    2
2021-Jan-16  05 19  +48 06   1.738   0.869   139E   Aur  11.9    82    2
2021-Jan-21  05 23  +48 28   1.785   0.943   135E   Aur  12.3    82    2
2021-Jan-26  05 27  +48 41   1.833   1.020   132E   Aur  12.7    81    1
2021-Jan-31  05 33  +48 45   1.882   1.100   128E   Aur  13.0    81    1
2021-Feb-05  05 39  +48 43   1.931   1.184   125E   Aur  13.4    81    1
  Comet Magnitude Parameters --- H = 8.0, 2.5n = 18.4, Offset = +5 days

 

88P/Howell – Though over three months since its September 28 perihelion at 1.35 au, Jupiter-family comet 88P/Howell has been slow to fade. After brightening to between magnitude 8.5 and 9.0 in September/October, 88P faded to between magnitude 9.1 and 10.0 in December as estimated by visual observers Michel Deconinck, J. J. Gonzalez, and Chris Wyatt. 88P should continue to fade in January as it moves through Aquarius in the evening sky though it becomes a difficult object for southern observers as the month progresses. Comet 88P/Howell is next at perihelion in March 2026 when it may peak at ~9.5.

 

88P/Howell
T = 2020-Sep-26  q = 1.35 au                                      Max El
Jupiter-family comet – 5.47-year orbital period                    (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021-Jan-01  22 15  -14 05   1.700   2.154    50E   Aqr  10.5    24    9
2021-Jan-06  22 28  -12 41   1.730   2.216    48E   Aqr  10.6    23    8
2021-Jan-11  22 41  -11 18   1.761   2.279    46E   Aqr  10.7    23    6
2021-Jan-16  22 54  -09 54   1.792   2.343    45E   Aqr  10.9    22    5
2021-Jan-21  23 06  -08 32   1.824   2.407    43E   Aqr  11.0    21    3
2021-Jan-26  23 18  -07 10   1.856   2.472    41E   Aqr  11.2    20    2
2021-Jan-31  23 30  -05 49   1.889   2.537    39E   Aqr  11.3    19    1
2021-Feb-05  23 41  -04 29   1.922   2.602    37E   Aqr  11.4    18    0
           Comet Magnitude Parameters --- H = 6.5, 2.5n = 10.0

 

156P/Russell-LINEAR – The next comet on our list continues the trend of fading comets. 156P is an object that rarely shows discernable cometary activity. Surprisingly, 2020 saw the comet brightening to magnitude 9.5-10.0 as it neared a 2020 November 17 perihelion at 1.33 au and close approach to 0.48 au from Earth.

 

In December, Michel Deconinck, J. J. Gonzalez, and Chris Wyatt observed 156P between magnitude 9.7 and 10.8 which suggests it hasn’t changed much in brightness since November. This month, the comet should start to fade as it moves through evening constellations of Pisces (Jan 1-8) and Triangulum (8-31).

 

156P/Russell-LINEAR
T = 2020-Nov-17  q = 1.33 au                                      Max El
Jupiter-family comet – 6.44-year orbital period                    (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021-Jan-01  01 11  +26 26   1.428   0.806   105E   Psc  10.8    77   11
2021-Jan-06  01 25  +28 33   1.449   0.851   104E   Psc  11.0    79    9
2021-Jan-11  01 38  +30 28   1.472   0.900   102E   Tri  11.1    80    7
2021-Jan-16  01 53  +32 11   1.496   0.950   101E   Tri  11.3    81    5
2021-Jan-21  02 07  +33 43   1.522   1.004    99E   Tri  11.5    81    4
2021-Jan-26  02 22  +35 05   1.549   1.059    98E   Tri  11.7    81    3
2021-Jan-31  02 38  +36 18   1.578   1.117    97E   Tri  11.9    80    3
2021-Feb-05  02 53  +37 20   1.607   1.177    95E   Per  12.1    78    2
           Comet Magnitude Parameters --- H = 9.7, 2.5n = 10.0

 

11P/Tempel-Swift-LINEAR – When a comet possesses three names, it usually means one of two things. Either the comet was discovered by three or more observers almost simultaneously (think 2018’s Machholz-Fujikawa-Iwamoto) or it was discovered across three or more apparitions. 11P is an example of the later. It acquired its first name on 1869 November 27 when Ernst Wilhelm Leberecht Tempel of Marseilles, France found it visually. The second name came on 1880 October 11 when Lewis Swift of Rochester, New York rediscovered the comet (also visually). After being seen in 1891 and 1908, 11P then went unobserved for 93 years. Its third name was the result of yet another re-discovery, this time by the CCD equipped LINEAR survey on 2001 December 7.

 

11P is now significantly fainter than it was a century or more ago. The intrinsic fading could be a result of an increasing perihelion distance from 1.06 au in 1869, 1.09 au 1891, and 1.15 au in 1908 to 1.58 au in 2001. After a close approach to Jupiter in September 2018 (0.60 au), 11P’s perihelion dropped back down to 1.39 au. The lower perihelion on 2020 November 26 and minimum comet-Earth distance of 0.49 au on November 3 have resulted in 11P reaching its brightest in over a century.

 

Magnitude brightness reports for this comet are quite scattered. In December submissions to the COBS site ranged from 10.9 to 14.0. The brightness forecast below is heavily leaning toward the fainter end. This month, 11P is an evening object moving through Cetus (Jan 1-26) and Taurus (26-31) and should fade as it is moves away from the Sun and Earth.

 

11P/Tempel-Swift-LINEAR
T = 2020-Nov-26  q = 1.39 au                                      Max El
Jupiter-family comet – 5.95-year orbital period                    (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021-Jan-01  02 17  +06 21   1.444   0.736   113E   Cet  13.9    56   36
2021-Jan-06  02 30  +06 10   1.459   0.778   111E   Cet  14.1    56   36
2021-Jan-11  02 44  +06 07   1.477   0.821   109E   Cet  14.3    56   36
2021-Jan-16  02 57  +06 10   1.496   0.868   107E   Cet  14.4    56   35
2021-Jan-21  03 10  +06 19   1.517   0.917   105E   Cet  14.6    56   35
2021-Jan-26  03 24  +06 32   1.539   0.969   103E   Cet  14.8    57   35
2021-Jan-31  03 36  +06 47   1.562   1.023   102E   Tau  15.0    57   35
2021-Feb-05  03 49  +07 05   1.587   1.080   100E   Tau  15.2    57   35
           Comet Magnitude Parameters --- H = 13.0, 2.5n = 10.0

 

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

 

On November 19, 29P underwent another of its frequent outbursts. Since then, the comet has stayed between magnitude 12-14 in the evening sky in Aries. If you image 29P, please consider contributing to the British Astronomical Society’s (BAA) 29P monitoring program coordinated by Richard Miles. You can find more information at the BAA’s “Observing the outbursting comet 29P/Schwassmann-Wachmann” page ( https://britastro.org/node/18562 ).

 

29P/Schwassmann-Wachmann

T = 2019-Mar-07  q = 5.77 au                                     Max El
Centaur comet - 14.8-yr orbital period                            (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2020-Jan-01  02 15  +24 24   5.847   5.313   118E   Ari  12-14   74   20 
2020-Jan-06  02 15  +24 15   5.848   5.385   113E   Ari  12-14   74   18
2020-Jan-11  02 15  +24 07   5.849   5.461   108E   Ari  12-14   74   17
2020-Jan-16  02 16  +24 01   5.851   5.539   103E   Ari  12-14   74   15
2020-Jan-21  02 17  +23 57   5.852   5.618    98E   Ari  12-14   73   13
2020-Jan-26  02 18  +23 54   5.853   5.699    94E   Ari  12-14   71   12
2020-Jan-31  02 19  +23 52   5.854   5.780    89E   Ari  12-14   69   10
2021-Feb-05  02 21  +23 52   5.855   5.861    84E   Ari  12-14   65    9

 

141P/Machholz - Former ALPO Comet Section Coordinator Don Machholz discovered this Jupiter-family comet in 1994. With a 5.34-year period, 141P is making its 5th observed perihelion passage. During 1994 the comet was actually a multiple comet with 5 components (component D was even observed to split during the apparition). The two brightest components (the primary A and secondary D) made a visually striking double comet in small telescopes. Components A and D were re-observed in 1999 but by 2005 only component A was visible. Due to poor observing conditions, no components were seen in 2010. During the last return in 2015, the primary (A) has been seen as well as another component (H) which could have been a new sighting of components B or C observed back in 1994.

 

141P’s split personality didn’t begin in 1994. Research by Zdenek Sekanina found that components B through E split from the primary during the period of 1987 to 1991. Other research suggests 141P (or its progenitor) may have been breaking up for some time as it is related to both the Alpha Capricornid meteor shower and comet 169P/NEAT (a weakly active comet on an orbit with a 4.2-year period).

 

During the current apparition, CCD imagers have detected two additional fainter components. We are still awaiting an official announcement of these two fainter components and whether they are new components or a return of previously observed components.

 

141P is an evening object moving through Aquarius (Jan 1-10) and Cetus (10-31). With perihelion on December 16 at 0.81 au and closest approach to Earth on January 19 at 0.53 au, 141P should be near its peak brightness as January begins. Recent submissions to COBS suggest the comet is around magnitude 10.5 as January beings.

 

141P/Machholz
T = 2020-Dec-16  q = 0.81 au                                      Max El
Jupiter-family comet – 5.34-year orbital period                    (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021-Jan-01  22 47  -08 31   0.852   0.589    59E   Aqr  10.5    33   12
2021-Jan-06  23 23  -08 06   0.881   0.556    62E   Aqr  10.5    34   15
2021-Jan-11  00 01  -07 32   0.915   0.533    66E   Cet  10.6    37   19
2021-Jan-16  00 41  -06 46   0.954   0.521    71E   Cet  10.9    39   23
2021-Jan-21  01 22  -05 48   0.997   0.521    76E   Cet  11.2    41   27
2021-Jan-26  02 01  -04 40   1.043   0.532    80E   Cet  11.6    43   31
2021-Jan-31  02 39  -03 27   1.091   0.556    85E   Cet  12.1    45   35
2021-Feb-05  03 13  -02 13   1.141   0.590    89E   Eri  12.6    47   37
           Comet Magnitude Parameters --- H = 9.4, 2.5n = 10.0

 

398P/Boattini - Comet Boattini was discovered on 2009 August 26 as an 18-19th magnitude object by Andrea Boattini with the 0.7-m Catalina Schmidt. During its 2009 return, the comet was a reasonably bright object reaching 12-13th magnitude. It was missed at its next return in 2015 but was recently recovered on 2020 August 11 at 19th magnitude by the ATLAS survey.  Observing circumstances are near optimal for its current orbit with perihelion occurring on 2020 December 17 at 1.31 au and closest approach to Earth a few days later on December 22 at 0.38 au. Chris Wyatt and J. J. Gonzalez both observed the comet in December at magnitude 11.0 to 12.8. 398P is currently at its brightest and should start to fade this month as it moves through Eridanus (Jan 1), Orion (1-27) and Taurus (27-31) in the evening sky.

 

398P/Boattini
T = 2020-Dec-26  q = 1.31 au                                      Max El
Jupiter-family comet – 5.53-year orbital period                    (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021-Jan-01  04 46  -00 10   1.307   0.381   142E   Eri  11.8    50   50
2021-Jan-06  04 52  +02 52   1.311   0.389   141E   Ori  11.8    53   47
2021-Jan-11  05 00  +05 57   1.317   0.400   140E   Ori  11.9    56   44
2021-Jan-16  05 09  +09 01   1.326   0.416   139E   Ori  12.0    59   41
2021-Jan-21  05 18  +11 59   1.337   0.435   137E   Ori  12.2    62   38
2021-Jan-26  05 28  +14 45   1.351   0.458   135E   Ori  12.3    65   35
2021-Jan-31  05 39  +17 17   1.366   0.485   133E   Tau  12.5    67   33
2021-Feb-05  05 51  +19 32   1.384   0.516   131E   Ori  12.7    70   30
           Comet Magnitude Parameters --- H = 12.7, 2.5n = 10.0

 

C/2019 N1 (ATLAS) – Yet another ATLAS discovery may be within range of visual observers, albeit those with larger apertures. C/2019 N1 was discovered back on 2019 July 5 at 18th magnitude and 6 au from the Sun. As is characteristic for a dynamically new long-period comet, N1 has brightened very slowly since discovery. Combine that with the fact that it came to perihelion on 2020 December 1 at 1.70 au on the far side of the Sun, and there is little expectation of N1 becoming brighter than about 11th magnitude. This month, the comet is climbing higher into the morning sky though it is only visible from the southern hemisphere as it moves through Centaurus (Jan 1), Lupus (1-17), Circinus (17-28), and Triangulum Austrinus (28-31).

 

C/2019 N1 (ATLAS)
T = 2020-Dec-01  q = 1.70 au                                      Max El
Long-period comet – Dynamically new                                (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021-Jan-01  14 30  -42 15   1.750   2.104    55M   Cen  11.7     3   33
2021-Jan-06  14 36  -46 04   1.766   2.061    58M   Lup  11.7     0   38
2021-Jan-11  14 42  -50 00   1.784   2.022    61M   Lup  11.7     0   43
2021-Jan-16  14 48  -54 04   1.805   1.988    64M   Lup  11.7     0   47
2021-Jan-21  14 55  -58 15   1.827   1.960    67M   Cir  11.7     0   50
2021-Jan-26  15 02  -62 30   1.851   1.938    70M   Cir  11.7     0   52
2021-Jan-31  15 10  -66 48   1.877   1.922    72M   TrA  11.7     0   53
2021-Feb-05  15 19  -71 07   1.905   1.914    74M   TrA  11.8     0   52
           Comet Magnitude Parameters --- H = 8.0, 2.5n = 8.5

 

C/2020 R4 (ATLAS) – Back in the ALPO Comet News for October 2020, I suggested that we keep an eye on C/2020 R4 (ATLAS). With a perihelion on March 1 at 1.03 au and a close approach with Earth on April 23 at 0.46 au, R4 could become a nice object if it brightens rapidly. At discovery on 2020 September 12 it was a faint 18th magnitude. Since then, the comet is showing some promise with observers placing it as bright as 11-13th magnitude in mid-December.

 

As January begins, R4 is diving towards the Sun. In fact, it is already lost to most southern observers and will be lost to northern observers by the 2nd week of the month. Expected to be fainter than 11th magnitude, there may be few observations made before we lose it to the Sun’s glare. The good news is that the comet will reappear to ground-based observers in late February to early March. At its brightest in late April, R4 may be an easy target for small aperture visual observers (8-9th magnitude though this is still highly uncertain).

 

C/2020 R4 (ATLAS)
T = 2021-Mar-01  q = 1.03 au                                      Max El
Long-period comet – ~942-year orbital period                       (deg)
    Date      R.A.   Decl.     r       d    Elong  Const  Mag   40N  40S
2021-Jan-01  21 17  -18 57   1.420   2.101    35M   Cap  11.8    11    2
2021-Jan-06  21 14  -18 25   1.368   2.132    29M   Cap  11.7     8    0
2021-Jan-11  21 10  -17 54   1.317   2.153    23M   Cap  11.6     3    0
2021-Jan-16  21 07  -17 22   1.269   2.164    18M   Cap  11.5     0    0
2021-Jan-21  21 05  -16 49   1.224   2.164    12M   Cap  11.4     0    0
2021-Jan-26  21 02  -16 16   1.181   2.152     7M   Cap  11.2     0    0
2021-Jan-31  20 59  -15 41   1.143   2.127     2M   Cap  11.1     0    0
2021-Feb-05  20 56  -15 06   1.109   2.090     4M   Cap  11.0     0    0
           Comet Magnitude Parameters --- H = 9.0, 2.5n = 8.0

 

New Discoveries, Recoveries and Other Comets in the News

 

Newly Numbered Periodic Comets –

 

397P/Lemmon   = P/2012 SB6  = P/2020
398P/Boattini   = P/2009 Q4  = P/2020 P2
399P/PANSTARRS   = P/2013 O2  = P/2020 O4
400P/PANSTARRS   = P/2013 PA104 = P/2020 R1
401P/McNaught   = P/2006 H1  = P/2020 R3
402P/LINEAR   = P/2002 T5  = P/2020 Q3
403P/Catalina   = P/2007 VQ11  = P/2020 T1
404P/Bressi   = P/2011 U2  = P/2020 M6
405P/Lemmon   = P/2013 TL117  = P/2020 U1
406P/Gibbs   = P/2007 R2 = P/2020 R8
407P/PANSTARRS-Fuls  = P/2013 J4  = P/2019 Y2
408P/Novichonok-Gerke  = P/2011 R3 = P/2020 M7
409P/LONEOS-Hill  = P/2005 XA54  = P/2020 V1

 

C/2020 X3 (SOHO) – This was the comet mentioned in the above write-up for C/2020 S3 (Erasmus). Prolific discoverer of SOHO comets, Worachate Boonplod of Samut Songkhram, Thailand, found this comet in LASCO C3 data taken on December 13. Only hours after Worachate’s discovery, C/2020 X3 was imaged by A. Moeller and Nick James during the December 14 Total Solar Eclipse. Karl Battams (Naval Research Lab) was able to also find images of the comet in STEREO-A COR-2 data on December 14. At its brightest the comet was around magnitude 5.1. A small Kreutz sungrazing comet with a perihelion on December 14.94 UT at 0.005 au, C/2020 X3 started to fade prior to perihelion and likely did not survive its extremely close brush with the Sun.

 

P/2020 X2 (ATLAS) – The Asteroid Terrestrial-Impact Last Alert System, or ATLAS, found this 18th magnitude short-period comet on December 10 with their 0.5-m f/2 astrograph at Mauna Loa on the big island of Hawaii. Pre-discovery observations on 7 nights going back to 2020 September 25 were also found (observations by ATLAS, Mount Lemmon, Pan-STARRS, and ZTF). P/2020 X2 is a Halley-type comet with an orbital period of 66 years and perihelion on 2020 November 16 at 3.83 au. The comet’s next perihelion will be in 2087.

 

P/2020 X1 (ATLAS) – ATLAS found this 18th magnitude short-period comet on December 4, though this time it was their 0.5-m f/2 astrograph at Haleakala on the Hawaiian island of Maui that made the discovery. Pre-discovery observations made from December 1 to 3 by ATLAS, the Catalina Sky Survey 0.7-m Schmidt, and Pan-STARRS were also found. Based on a 7-day arc, P/2020 X1 appears to be a short-period comet with an orbital period of 9.7 years and perihelion on 2020 July 20 at 2.88 au. P/2020 X1 has likely already peaked in brightness and should fade as it moves away from perihelion and its minimum distance to Earth.

 

P/2020 W2 = P/2003 WR168 = P/2005 CR16 (LINEAR-NEAT) – On November 16, Catalina observer David Rankin found a 19th magnitude comet in images taken with the 1.5-m Mount Lemmon reflector. David had one productive observing run. Across two nights (Nov 15 & 16), he discovered 2 new comets and serendipitously recovered two more comets, including this one (P/2020 W2). After the object was posted on the MPC PCCP, H. Sato recognized the object as a return of an object that was designated as an asteroid twice in the past as 2003 WR168 (discovered by NEAT at 19th magnitude on 2003 November 19) and 2005 CR16 (discovered by LINEAR at 19-20th magnitude on 2005 February 2).

 

While the object as still on the NEOCP, Eric Christensen, the PI of the Catalina Sky Survey, reached out to me regarding some observations of the object that I made in 2005. At the time I was regularly imaging asteroids on cometary orbits to detect any activity. A re-examination of my 1.5-m University of Arizona Kuiper reflector data from 2005 March 8 did uncover a faint diffuse coma and possible tail. Sam Deen was also able to find archival 3.6-m Canada-Hawaii-France Telescope data from 2005 April 11 that also showed a coma and tail.

 

We now know that P/2020 W2 = P/2003 WR168 = P/2005 CR16 (LINEAR-NEAT) is an active comet on a 17.1-year orbit. Perihelion occurs on 2021 June 23 at 3.26 au. With such a large perihelion distance, P/LINEAR-NEAT is at it brightest at opposition in 2020 November and 2022 February. It will be around magnitude 20 at both oppositions.

 

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 < carl.hergenrother @ alpo-astronomy.org >.

 

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

 

Stay safe and enjoy the sky!
- Carl Hergenrother (ALPO Comets Section Coordinator)

Edited by Carl H., 03 January 2021 - 04:24 AM.

[Rich (RLTYS)]

Thanks, got to have my monthly fix of ALPO Comet News. 

[Zorbathegeek]

I'm with you there Rich'. The next comet that may come within range from my very southern, urban location, is 67P/Churyumov-Gerasimenko, in December. Then it's C/2017 K2 (PanSTARRS), the following March/April. So, in the meantime, I love the vicarious cometary enjoyment these reports give me. Here's to bright discoveries and major outbursts.

 

Ray.

[Aquarellia]

Nice journal, nice souvenirs of 2020 and lot of "comet hope" for 2021 !

Thank you for your work Carl !

Michel

[Octans]

Just to get ahead of inevitable hyperbolic media claims that tend to go viral, because that's what happens every single time this happens: There's a newly discovered comet that will probably be called either C/2021 A1 or A2 and could make a nice binocular or even naked eye comet in December. Currently called C4AGJ62: https://cneos.jpl.na.../object/C4AGJ62 (link will break once the name is finalized) Will get very close to Earth (0.2 au) while decently close to the Sun (0.8 au) under about the best observing circumstances possible for the Northern Hemisphere, and could reach magnitude 2-3 while deep in twilight *if things go very well*, which includes brightening normally for a distantly active comet (n=3) and a possible but brief <4 magnitude spike from forward scattering on December 14. It has some potential to be a brilliant great comet *from Venus* which it'll pass well within 0.1 au of.

 

This has all the hallmarks of a nice comet-of-the-year (or even several years) that gets unfairly turned into the disappointment-of-the-year because someone decides to extrapolate a short-lived outburst (which are to be expected, but last at most a few days) out to perihelion and then proceed to claim it's going to be brighter than the moon, something completely unphysical for such a small comet. You can look to recent examples of similar hyped up comets like C/2017 S3 (PANSTARRS) and C/2010 X1 (Elenin) for realistic examples of what this comet could do (though favorable geometry means this one could be a few magnitudes brighter).

 

Anyways, hype aside, just an FYI of something to look forward to later this year.

Edited by Octans, 05 January 2021 - 06:34 AM.

[Carl H.]

Yeah, there is a lot to unpack with this one.

 

The key to its upcoming brightness is whether this comet is dynamically new (i.e., on its first visit to the inner solar system) or old (has been in the inner solar system before). If dynamically new, its current brightness may be due to the sublimation of extremely volatile ices. The coma we are currently observing may have been released at even larger heliocentric distances meaning the comet's current brightness is more indicative of past, than current, activity. Due to the rapid depletion of the most volatile ices, C4AGJ62 could brighten at a slow rate, or even intrinsically fade;  underperforming many's speculative predictions. Dynamically new comets are also prone to falling apart as was seen with ISON, Elenin, and others. Hopefully we'll know more once an official orbit it published though it may take a few more months of observations before we'll know for sure.

 

The high phase angle reaches a maximum of ~160 degrees which could result in an enhanced brightness of ~4 magnitudes. But, this is only if the comet is dusty. If it is gassy with poor dust production, the high phase angle will produce a much weaker, if any, enhancement. 

 

At the risk of being very wrong, the assumption of a current brightness of 19.0 and 2.5n ~ 7.5 rate of brightening results in a peak brightness of 5.8. Adding ~4 magnitude of forward scattering enhancement results in a peak brightness of magnitude 1.8, but... the comet is only 15 degrees from the Sun at that time and only a few degrees above the horizon at the end of nautical twilight in the evening and start of nautical twilight in the morning for northern observers. If the comet is fainter, it will be very difficult to see. If brighter, we may be able to enjoy the comet in both the evening and morning sky for a few days when it is at its brightest.

 

Regardless, 2021 is already looking like a fun comet year.

[Carl H.]

We may not have long to wait as to whether C4AGJ62 is dynamically old or new. Many pre-discovery observations going back to April 2020 have been found. We should have our answer when the official MPEC and/or CBET is released.

[Octans]

Seems like the MPC might be waiting for N00ht7m (which was discovered 0.5 days before C4AGJ62) before announcing C4AGJ62, to make the latter C/2021 A2 instead of A1. Could still be several more days before the announcement if that's the case, as N00ht7m still has a rather poorly constrained orbit.

[Rankinstudio]

This is neat, I didn't know you did these reports Carl. I'll keep an eye out for more.

 

Cheers

[Octans]

Floodgates are open! C/2021 A1 (Leonard): https://www.minorpla...K21/K21A99.html

 

JPL also just loaded the comet, and it looks to be dynamically old, with barycentric a ~ 1700 au in year 1600: https://ssd.jpl.nasa...cgi?sstr=2021A1 Very unlikely now for the comet to disintegrate, although old comets tend to not be as dusty.

Edited by Octans, 10 January 2021 - 12:31 AM.

[Zorbathegeek]

Thanks Octans. I just added that to Stellarium, and It looks quite promising.

 

Ray.

Edited by Zorbathegeek, 10 January 2021 - 02:43 AM.

[BrooksObs]

Floodgates are open! C/2021 A1 (Leonard): https://www.minorpla...K21/K21A99.html

 

JPL also just loaded the comet, and it looks to be dynamically old, with barycentric a ~ 1700 au in year 1600: https://ssd.jpl.nasa...cgi?sstr=2021A1 Very unlikely now for the comet to disintegrate, although old comets tend to not be as dusty.

Quite to the contrary, dynamically "old" comets are the dustiest among these objects, at least the larger, more spectacular ones, with their photometric parameter values of "n" occasionally being as low as only n= 2.5 (i.e. more like simple reflecting bodies).

 

I would further note that JPL's photometric parameters for 2021A!, Leonard, appear rather wildly optimistic (just as they were with ISON) to me, suggesting that the comet's intrinsic brightness could be as high at +5.3 . I would suggest that a far more realistic figure might be around +8.0 , making the comet little brighter than the brightest of Jupiter's family of comets. This may also open the door to suggestions that the comet might not even be able to survive perihelion passage! We'll have to see  what the first visual magnitudes reported have to say about the comet before much more can be said regarding its future.

 

BrooksObs

Edited by BrooksObs, 10 January 2021 - 04:38 PM.

[Octans]

Quite to the contrary, dynamically "old" comets are the dustiest among these objects, at least the larger, more spectacular ones, with their photometric parameter values of "n" occasionally being as low as only n= 2.5 (i.e. more like simple reflecting bodies).

This paper led by Oort himself says otherwise: http://adsabs.harvar...BAN....11..259O That trend has more or less held up in recent years (so so looking at more typically sized comets here), with the new comets about twice as likely to be dusty in the vicinity of 1-2 au as old comets (very close in and very far out, they tend to all look dusty).

 

C/2021 A1 is in all likelihood not a particularly big comet. Being dynamically old does put a soft floor on its size though (it's unlikely to have survived its previous apparition if it's as small as new comets C/2017 S3 and C/2010 X1, which were similarly bright this far out). Quite rare for a dynamically old comet with such a low perihelion distance to be visibly active so far out though, like a Hale-Bopp that's 10 magnitudes fainter. An exact Hale-Bopp+10 would be actually be an extremely excellent scenario for this comet as the very favorable geometry of C/2021 A1 + dustiness of Hale-Bopp offsets most of that 10 mag difference and would produce a peak near mag 0-1 (albeit in twilight). A peak near 2-4 is probably more likely though, and would happen if it either doesn't bright as fast or isn't as dusty as Hale-Bopp. It probably won't behave like a mini Hale-Bopp though, as 10 mag difference is a factor of 100 in diameter, giving a ~0.4 km nucleus, and that's probably too small to have survived perihelion last time around.

 

In any case, even if it turns out to be a fairly gassy comet, it will likely temporarily take on the appearance of a dusty one for a few days near closest approach as the dust part of the brightness is boosted by 4 mag. It just wouldn't be as bright or impressive as if it already looked dusty before the boost.

Edited by Octans, 10 January 2021 - 07:47 PM.

[BrooksObs]

This paper led by Oort himself says otherwise: http://adsabs.harvar...BAN....11..259O That trend has more or less held up in recent years (so so looking at more typically sized comets here), with the new comets about twice as likely to be dusty in the vicinity of 1-2 au as old comets (very close in and very far out, they tend to all look dusty).

 

C/2021 A1 is in all likelihood not a particularly big comet. Being dynamically old does put a soft floor on its size though (it's unlikely to have survived its previous apparition if it's as small as new comets C/2017 S3 and C/2010 X1, which were similarly bright this far out). Quite rare for a dynamically old comet with such a low perihelion distance to be visibly active so far out though, like a Hale-Bopp that's 10 magnitudes fainter. An exact Hale-Bopp+10 would be actually be an extremely excellent scenario for this comet as the very favorable geometry of C/2021 A1 + dustiness of Hale-Bopp offsets most of that 10 mag difference and would produce a peak near mag 0-1 (albeit in twilight). A peak near 2-4 is probably more likely though, and would happen if it either doesn't bright as fast or isn't as dusty as Hale-Bopp. It probably won't behave like a mini Hale-Bopp though, as 10 mag difference is a factor of 100 in diameter, giving a ~0.4 km nucleus, and that's probably too small to have survived perihelion last time around.

 

In any case, even if it turns out to be a fairly gassy comet, it will likely temporarily take on the appearance of a dusty one for a few days near closest approach as the dust part of the brightness is boosted by 4 mag. It just wouldn't be as bright or impressive as if it already looked dusty before the boost.

 

Rubbish.The fact of the matter is that precious little meaningful photometric data was available in the years before 1951 to work with. I can't say where Oort, et al. got their or how it was reduced, but their conclusions are just wrong. Had the paper been written after the great comet influx seen between 1957 and 1976 (consisting of many dusty, low n comets) the conclusions undoubtedly would have been very different.

 

Sorry, but I have to add that neither have my own data from scores of comets observed in recent decades supported Oort's paper. MOST of the well observed larger dynamically "old" objects that were dusty had values of "n" lower than 4 , with the sole exception of Comet McNaught. On the other hand, "new " icy comets constituted mainly those ones that were mistakenly taken to be much brighter than they really were and initially developed faster, only to slow down at the last minute as they approached the Sun due to their modest reserves of highly volatile ices being expended, after falsely giving the comet an apparent n= 5 or even 6 early on. These are also the objects most likely to disintegrate at, or prior to, perihelion due to the fragility of their nuclei. "Dusty" comets s are much more solid in nature and capable of perihelion survival even if relatively small.

 

Neither is it unusual today to discover dynamically "old" comets out this far from the Sun in my opinion. Its just that until recently we did not have ongoing survey's capable of doing so. Nor do I see any reasonable comparison to Hale-Bopp, even with the latter's Ho decreased by 10 (!) magnitudes, no matter how the the data is massaged. H-B was a unique object of giant proportions not resembling anything seen since the early 19th century. So there is no reason to assume any potential for C/2021 A1 reaching a peak of 0-1 magnitude through any manner of comparison with H-B. In fact, I wouldn't venture the comet exceeding magnitude +4 at peak whendeep in twilight from the data so far available. 

 

We currently are also at a definite disadvantage in that most amateur cometary photometric data is being improperly reduced these days, consistently resulting in higher values of "Ho" and"n" than they rightfully should be. This has been a definite factor in the misjudging of the future brightness of newly discovered comets of less than 1.0 a.u. perihelia over the past twenty years.

 

Finally, C/2020 A1 orbit has a very nearly parabolic solution currently. So it would not surprise me if it turns out to actually be parabolic and "new " rather than "old". If so, it could turn out to be a real stinker a year from now.

 

BrooksObs

Edited by BrooksObs, 10 January 2021 - 09:59 PM.

[Octans]

Rubbish.The fact of the matter is that precious little meaningful photometric data was available in the years before 1951 to work with. I can't say where Oort, et al. got their or how it was reduced, but their conclusions are just wrong. Had the paper been written after the great comet influx seen between 1957 and 1976 (consisting of many dusty, low n comets) the conclusions undoubtedly would have been very different.

 

Sorry, but I have to add that neither have my own data from scores of comets observed in recent decades supported Oort's paper. MOST of the well observed larger dynamically "old" objects that were dusty had values of "n" lower than 4 , with the sole exception of Comet McNaught. On the other hand, "new " icy comets constituted mainly those ones that were mistakenly taken to be much brighter than they really were and initially developed faster, only to slow down at the last minute as they approached the Sun due to their modest reserves of highly volatile ices being expended, after falsely giving the comet an apparent n= 5 or even 6 early on. These are also the objects most likely to disintegrate at, or prior to, perihelion due to the fragility of their nuclei. .

 

Neither is it unusual today to discover dynamically "old" comets out this far from the Sun in my opinion. Its just that until recently we did not have ongoing survey's capable of doing so. Nor do I see any reasonable comparison to Hale-Bopp, even with the latter's Ho decreased by 10 (!) magnitudes, no matter how the the data is massaged. H-B was a unique object of giant proportions not resembling anything seen since the early 19th century. So there is no reason to assume any potential for C/2021 A1 reaching a peak of 0-1 magnitude through any manner of comparison with H-B. In fact, I wouldn't venture the comet exceeding magnitude +4 at peak whendeep in twilight from the data so far available. 

 

We currently are also at a definite disadvantage in that most amateur cometary photometric data is being improperly reduced these days, consistently resulting in higher values of "Ho" and"n" than they rightfully should be. This has been a definite factor in the misjudging of the future brightness of newly discovered comets of less than 1.0 a.u. perihelia over the past twenty years.

 

Finally, C/2020 A1 orbit has a very nearly parabolic solution currently. So it would not surprise me if it turns out to actually be parabolic and "new " rather than "old". If so, it could turn out to be a real stinker a year from now.

 

BrooksObs

Oort's paper had more than enough capability to determine whether a comet is dusty or gassy, which is the only reason I brought it up. I did not bring up what it found in terms of photometric brightening, as that has been long superceded by more recent works with higher precision, nor did I ever suggest n>4 in anything I said above. Even my optimistic scenario of Hale-Bopp-like brightening is n<4. Moreover, McNaught was almost certainly a dynamically new comet, and if your sources say otherwise, you should revisit the reliability of those sources, especially as it's one of so few bright comets from recent times that are plausibly dynamically new, alongside Kohoutek, Seki-Lines, and Arend-Roland.

 

The Catalina Sky Survey, which discovered C/2021 A1, has been around for over a decade now. In that time, it and other major surveys like Pan-STARRS and ATLAS have discovered many dynamically old and new comets that venture within 1 au of the Sun. If you actually look at the survey data, you'll find that the majority of these distantly discovered comets with low perihelia are dynamically new, even though most discovered comets are dynamically old. It's simple statistics with a simple explanation: (1) new comets are simply brighter for the size, as old comets no longer have a surface of fresh hypervolatile ice, and (2) old comets would have been destroyed if they were too small to survive perihelion, so only big ones are left (with the exception of fragments that split off bigger comets one orbit before, but such comet families are relatively rare).

You should also revisit your numbers on C/2021 A1: this comet will reach magnitude 4 in twilight if it remains very dusty even at n=2---that is, no further increase in dust activity at all. The only realistic way it can peak at less than mag 4 is if it not only brightens incredibly slowly, but *also* becomes very gassy. If it's even moderately dusty while brightening at n=3, which is by no means far fetched, it will reach at least magnitude 3. However, most people will not see the comet this bright not only because of twilight, but because this maximum brightness lasts only a couple days, and even a week of bad weather will dramatically dampen the display. For this reason, I expect there will be a lot of disappointment in this comet, even on the off chance it turns out to be quite spectacular, at no fault of its own. As far as I can tell, there has not been a comet with forward scattering geometry this favorable for ground-based observers (i.e., non-daylight observations) in many decades, even if the comet itself is not intrinsically noteworthy.

 

Finally, you cannot see whether a comet is old or new from the present day heliocentric osculating solution. If this is how you've been distinguishing old vs. new comets in your data set, you should most definitely revisit your data. You must integrate the comet's trajectory backwards in time to a point before it entered the planetary region and then use the barycentric orbital solution to determine what it's orbit looked like before it was perturbed by the planets and the associated reflex motion of the Sun. That was the key piece of work Jan Oort did that he is now most renowned for. For C/2021 A1, the barycentric solution in year 1600.0 has an eccentricity of 0.99966 +/- 0.00002, and a semi-major axis of 1700 +/- 100 au (vs. >50000 au for new comets). The formal errors are usually understated, but for this comet, the solution is so far away from the Oort spike that there's no realistic chance this comet is new, absent unprecedentedly large non-gravitational forces. Keep in mind that we already have a nine month observational arc for this comet.

Edited by Octans, 11 January 2021 - 12:52 AM.

[BrooksObs]

Octans, my only advice to you, since you attempt to make long controversial discussions about anything that I post, is to watch and learn. You may indeed benefit from that approach. In the mean time, I don't have the time to waste responding to your posts.

 

BrooksObs

[Octans]

Octans, my only advice to you, since you attempt to make long controversial discussions about anything that I post, is to watch and learn. You may indeed benefit from that approach. In the mean time, I don't have the time to waste responding to your posts.

 

BrooksObs

I only comment on your posts if and when I see points stated as facts that I know to be wrong, and always provide a detailed explanation as to why. In this case, you first commented on my post thinking I was wrong, and I provided a response as to why that does not appear to be the case. I will gladly revise my thinking and acknowledge so if you can make evidence-based arguments refuting my statements, which you have not. Anything less runs counter to science, and would be irresponsible not to challenge. I do not question your decades of observing experience, but that most certainly does not make you immune to ever being wrong as you imply.

Edited by Octans, 11 January 2021 - 02:46 PM.

[goodricke1]

I enjoy reading your posts Octans, your depth of knowledge is clear.

 

BrooksObs has made a worthy contribution to the community over long years of course; albeit his style can be somewhat intransigent and overbearing at times.

[Octans]

BrooksObs has made a worthy contribution to the community over long years of course; albeit his style can be somewhat intransigent and overbearing at times.

I should make clear that I tend to agree with this statement. I find no issues in the majority of his posts I come across (among the ones on topics that I consider myself familiar with, anyways) and normally don't comment on those unless I have something extra to add. Nobody's foolproof though, and we (myself included) all hold misconceptions and harbor personal biases on things we think we understand but which can often be readily disproven when pointed out.

[Jure Atanackov]

This 'let us not get our hopes up' theme crops up every time there is a new comet with at least a slight potential to become a bright object. It seems every time it goes pretty much along the same lines: let us not get our hopes up, let us not make bold predictions as the media will pick it up and blow it out of proportions, the media pick it up anyway and blow it out of proportions. And sometimes, rarely, the comet actually performs. There are more than enough people that have sufficient understanding of the factors that can make a comet bright. More than enough will or already have picked up on the comet's orbit and viewing geometry. It is only a matter of intrinsic brightness and dust production. In an age of clickbait online 'journalism' someone, somewhere will make a bold prediction and the media will pick it up. It happens with more or less every potentially good  comet. IMHO self-censorship will have no effect on this, only shut down potentially very interesting discussions. 

 

I actually enjoy these discussions, a lot. BrooksObs' contribution to the field, extensive experience and knowledge are widely recognized. I must have ready every Comet Digest published, and have followed his input on 'comets-ml' and here on CN for almost 20 years. Most of the time his predictions are spot on. Questioning widely accepted ideas and notions as well as challenging authority are an integral part of the scientific discourse. Science is not personal, it is about facts, observations, data, methods and interpretations, but not about the person. There is absolutely nothing personal, and that's what's great about it. From my fairly limited knowledge on comets I think Octans' questions and input is very much valid, interesting, deserves discussion and raises the quailty of this forum.

 

Back to the comet. The orbit is very interesting and gives potential for a very decent display. From past experience, I do not trust the published CCD magnitudes of faint comets, particularly from astrometric observations. There have been so many cases, where faint CCD magnitudes were being reported and suddenly someone decided to take a look and found the comet within visual range (like C/2006 P1 (McNaught) for example). Currently reported magnitudes indicate an intrinsically faint comet, but if it is picked up visually by April or May it will become much more interesting. I am cautiously optimistic about this comet (partly because I choose not to be pessimistic ).

CS!Jure

[cbellh47]

Hello Carl.
I read that Man-To Hui recovered comet 323P/SOHO from the ground using Suburu.  Rainer Kracht helped.
I think this is first observation of 323P from ground on 2020-Dec-21
He posted about it on Facebook with image.
https://www.facebook...1586080552244 
 

Must have been on the edge of solar elongation limit for Suburu.
Quite a remarkable achievement.

HORIZONS:

Date__(UT)__HR:MN     R.A._____(ICRF)_____DEC   T-mag   N-mag            delta      deldot    S-O-T /r    S-T-O
2020-Dec-21 00:00     14 13 28.97 -14 32 06.4    n.a.    n.a. 1.09228157394198 -37.5800648  53.2498 /L  57.4188

 

[Carl H.]

 

Hello Carl.
I read that Man-To Hui recovered comet 323P/SOHO from the ground using Suburu.  Rainer Kracht helped.
I think this is first observation of 323P from ground on 2020-Dec-21
He posted about it on Facebook with image.
https://www.facebook...1586080552244 
 

Must have been on the edge of solar elongation limit for Suburu.
Quite a remarkable achievement.

HORIZONS:

Date__(UT)__HR:MN     R.A._____(ICRF)_____DEC   T-mag   N-mag            delta      deldot    S-O-T /r    S-T-O
2020-Dec-21 00:00     14 13 28.97 -14 32 06.4    n.a.    n.a. 1.09228157394198 -37.5800648  53.2498 /L  57.4188

Thanks, Charles!

 

The object looks rather stellar in the Subaru image. Wonder if it will turn out to be another low-q asteroid, like 322P, rather than a traditional volatile-rich comet?