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ALPO Comet News for December 2021

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#1 Carl H.

Carl H.

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Posted 03 December 2021 - 04:15 AM

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

 

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

 

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 December 2021
Dec 02-03 – C/2021 A1 (Leonard) passes ~0.1 deg of 6th mag globular cluster M3
Dec 02 – 430P/Scotti at perihelion (q = 1.55 au, 5.5-year orbit, V ~ 17, 2nd observed return, discovered in 2011, missed at 2016 return)
Dec 04  – New Moon
Dec 06  – 19P/Borrelly orbit plane crossing
Dec 08  – C/2021 A1 (Leonard) orbit plane crossing
Dec 08 – 436P/Garradd at perihelion (q = 1.96 au, 14.4-year orbit, V ~ 19, 2nd observed return, discovered in 2007)
Dec 10  – First Quarter Moon
Dec 12 – C/2021 A1 (Leonard) passes ~0.2 deg of 9th mag globular cluster NGC 6366
Dec 12 – C/2021 A1 (Leonard) passes 0.2334 au (34.9 million km, 21.7 million miles) from Earth (Dec 12 – 13:53 UT)
Dec 14 – C/2021 A1 (Leonard) passes across bright emission nebula M16, the Eagle Nebula
Dec 14 – 402P/LINEAR at perihelion (q = 3.94 au, 18.6-year orbit, V ~ 16-17, 2nd observed return, discovered in 2003)
Dec 16 – 173P/Mueller at perihelion (q = 4.22 au, 13.6-year orbit, V ~ 19, very asymmetric lightcurve with peak activity 1-2 years BEFORE perihelion, peaked at V~16, 3rd observed return)
Dec 16 – P/2021 R1 (PANSTARRS) at perihelion (q = 4.89 au, 24.4-year orbit, V ~ 20, discovered last September)
Dec 18 – C/2021 A1 (Leonard) passes 0.0285 au (4.26 million km, 2.65 million miles) from Venus (Dec 18 - 02:06 UT), will appear 5.1 deg from Venus as seen from Earth
Dec 18  – Full Moon
Dec 18 – 221P/LINEAR at perihelion (q = 1.75 au, 6.4-year orbit, V ~ 19, currently in solar conjunction, 4th observed return, discovered in 2002)
Dec 19  – C/2017 K2 (PANSTARRS) orbit plane crossing
Dec 21 – C/2021 U4 (Leonard) at perihelion (q = 1.79 au, ~300-year orbit, V ~ 20-21)
Dec 21 – C/2021 R2 (PANSTARRS) at perihelion (q = 7.31 au, ~110,000-year orbit, V ~ 20)
Dec 21  – 8P/Tuttle orbit plane crossing
Dec 26  – Last Quarter Moon
Dec 30 – 395P/Catalina-NEAT at perihelion (q = 4.06 au, 16.8-year orbit, V ~ 17-18, 2nd observed return, discovered in 2005)
Dec 30-Jan 1 – 4P/Faye passes between 9th mag open cluster NGC 2254 and emission nebula IC 448

 

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

 

Orbit (from Syuichi Nakano, personal email)

 

   C/2021 A1 (Leonard)
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5 
T 2022 Jan. 3.29809 TT                                  Nakano
q   0.6152601            (2000.0)            P               Q
z  -0.0000451      Peri.  225.09163     +0.63774181     +0.29161284
 +/-0.0000011      Node   255.89505     +0.72791572     -0.53079785
e   1.0000277      Incl.  132.68632     -0.25184139     -0.79574845
From 1274 observations 2020 Apr. 11-2021 Nov. 18, mean residual 0".57.
  (1/a)org.= +0.000501, (1/a)fut.= -0.000105 (+/-0.000001), Q= 8.

 

Comet Magnitude Formula (from ALPO and COBS data)

 

m1 = 11.4 + 5 log d +  5.7 log r [T-325 to T-240 days, where T = date of perihelion]
m1 =  7.3 + 5 log d + 12.5 log r [T-240 to T-47 days]
m1 =  8.3 + 5 log d -  3.8 log r [from T-47 days and onward?]

 

As of December 2-3, C/2021 A1 (Leonard) is around magnitude 6.5, bright enough that some observers have reported it visible to the naked eye. Visual observers have also been observing a tail up to 0.75 degrees in length. Imagers have noted some interesting coma features, which unfortunately are sometimes associated with splitting or disruption events.

 

Eleven months ago, C/2021 A1 (Leonard) was discovered at 19th magnitude by Catalina Sky Survey astronomer Greg Leonard with the Mount Lemmon 1.5-m reflector when the comet was a distant 5.1 au from the Sun. The comet could have easily been discovered months earlier as pre-discovery observations from Mount Lemmon and PANSTARRS were found back to April 2020 when the comet was 7.5 au from the Sun. With a relatively small perihelion distance of 0.62 au in 2022 January and close approach to Earth on December 12 at 0.233 au (34.9 million km, 21.7 million miles), there was some excitement that Leonard could become a bright object.

The story of Comet Leonard has seen a few twists and turns. Based on the Pan-STARRS and Mount Lemmon photometry submitted to the Minor Planet Center, Leonard rapidly brightened throughout 2020 at a 2.5n ~ 11.7 rate. Between January and June 2021, that rapid brightening slowed significantly to a sluggish 2.5n ~ 5.6 rate suggesting activity was barely increasing beyond steady state. Six months ago, Leonard’s prospects weren’t looking good, but in July a new rapid brightening phase commenced. A fit to the photometry shows two possible brightening “legs” (2.5n ~ 20.6 between July and early October and 2.5n ~ 12.5 between early October and mid-November). Regardless of the exact fits or the number of “legs”, the comet brightened from apparent magnitude 17 to 8 and excitement started to build again.

 

Then something changed in mid-November. Since about November 16, Leonard has not only ceased its rapid brightening, but has faded in an absolute sense with a fading trend of 2.5n ~ -4. Leonard has faded by ~2 magnitudes after accounting for changes in heliocentric and geocentric distance. That is a dramatic decrease in activity for an inbound comet and suggests C/2021 A1 may not be healthy.

 

Fig1.jpg

 

Figure 1 - Brightness evolution of C/2021 A1 (Leonard) since the start of 2020. The comet photometry has been corrected foraperture,  phase angle effects as well as normalized to 1 au from the Earth and Sun. Data includes CCD/CMOS and visual photometry submitted to the ALPO and data submitted to the COBS site by Michael Lehmann.

 

Fig2.jpg

 

Figure 2 – Same data as above except plotted as aperture corrected apparent magnitude versus date. Plot produced in Seiichi Yoshida’s Comets for Windows.

 

Fig3.jpg

 

Figure 3 - Same as except only showing the most recent aperture corrected apparent magnitudes.

 

You may be wondering how a comet could intrinsically fade by two magnitudes while its apparent magnitude brightened from magnitude 8.2 to 6.8 over the same period. The reason is that between November 16 and December 3 Leonard’s distance to the Sun has fallen from 1.16 to 0.90 au and its distance to Earth from 1.06 to 0.45 au. Its phase angle has also increased from 52 to 86 degrees though that change should have only produced ~0.1 magnitudes of fading.

 

If you are having a sense of deja vue, you’re not alone. We saw a similar series of events in 2020 with C/2019 Y4 (ATLAS). Comet ATLAS was predicted to be a bright object but after brightening to ~7th magnitude about 2.5 months before perihelion, it’s brightening stalled and then enter a slow fade. A few weeks after the brightening stall, the nucleus was observed to have split into several smaller components. Could we be seeing the same with Leonard? Possibly. Leonard brightness stall and fading is similar to that of C/ATLAS. So far, we haven’t seen any sign of multiple nuclei, but then again it took a few weeks for ATLAS’ secondary nuclei to become visible.

 

So, for the next few paragraphs, let’s (mostly) focus on the things we can predict. Leonard starts the month at 0.93 au from the Sun and 0.52 au from Earth. On December 12, a minimum Earth-comet distance of 0.23 au is reached with the comet located 0.77 au from the Sun. Not only is the Earth-comet distance rapidly changing, but due to the comet passing Earth on its sunward side, Leonard’s phase angle increases from 80 degrees on the 1st to 160.5 degrees on the 14th. Such a large phase angle could produce up to 3 magnitudes of extra brightness due to forward scattering by small dust in the comet’s coma and tail. The exact amount of forward scattering remains to be seen and depends on the comet’s dust-to-gas ratio and whether it is still producing fine sized dust at that time, something that could be in question if it has disintegrated.

 

Leonard is a morning object only visible from the northern hemisphere as the month begins though it is rapidly diving towards the Sun. On December 2-3, it will pass through the outer region of the bright 6th magnitude globular cluster M3. By December 12, the comet will too close to the Sun to be observed outside of astronomical twilight. The next night, the comet shifts into the evening sky and will be within 18 degrees of the Sun but only a degree above the horizon by the end of nautical twilight. Unless the comet is bright (1st-2nd magnitude) and condensed (like last year’s NEOWISE) it may not be visible against such a bright sky. Unfortunately, the bright sky may prevent observation of Leonard photobombing two more deep sky objects: on December 12 is passes ~0.2 deg from 9th mag globular cluster NGC 6366 and on December 14 it passes over the bright emission nebula M16, the Eagle Nebula. How often do you see a comet pass over two Messier objects in an apparition, let alone in 12 days? The southern hemisphere finally gets their chance to observe the comet starting on December 17-18. The 18th also witnesses an extremely close approach to Venus of 0.0285 au (4.26 million km, 2.65 million miles). Here on the Earth the two will appear about 5.1 degrees apart.

 

The southern hemisphere will have the best views during the remainder of the month. While still visible from the northern hemisphere it will be a horizon hugger and only a few degrees above the horizon before the start of astronomical twilight. By the end of December, its distance to the Earth will have increased back to 0.83 au while its distance to the Sun continues to drop as it approaches perihelion on January 3 at 0.62 au. This month sees the comet move through the constellations of Canes Venatici (Dec 1-3), Boötes (3-8), Serpens (8-10), Hercules, (10-11), Ophiuchus (11-14), Scutum (14-15), Sagittarius (15-20), Microscopium (20-29), and Pisces Austrinus (29-31).

 

So now the difficult, or even foolish, discussion… how bright will Leonard get? We have a few complications: will the comet continue to intrinsically fade, or even disintegrate, and how much of an effect will dust forward scattering have? There are several scenarios that can play out. One could expect a resumption of the brightening trend and a 3-magnitude enhancement due to forward scattering. That would result in a 1st magnitude comet and perhaps visible even when at small elongations. Then again, if the fading continues and there is little to no forward scattering, a peak around 5-6th magnitude would result in Leonard being much too faint to be seen when located close to the Sun. The ephemeris below presents two scenarios: the magnitude in the ‘Mag NoFS’ column assumes the fading continues and there is no enhancement due to forward scattering (peak brightness of 5.6), the ‘Mag FS’ column also assumes the fading continues but with a maximum of ~3 magnitudes of forward scattering enhancement for a peak brightness of 2.0. I guess we’ll have to wait and see what happens.

 

C/2021 A1 (Leonard)                                                    Max El
                                                                       (deg)
    Date      R.A.   Decl.     r       d   PhAng Elong  Mag  Mag   40N      40S
                                                        NoFS  FS Ast Nau Ast Nau
2021 Dec 01  13 21  +29 58   0.931   0.522   80    68M  7.0  7.0  49  55   0   0
2021 Dec 02  13 30  +29 17   0.917   0.487   83    67M  6.9  6.9  47  54   0   0
2021 Dec 03  13 40  +28 27   0.902   0.453   86    66M  6.8  6.8  46  52   0   0
2021 Dec 04  13 52  +27 24   0.888   0.419   90    64M  6.6  6.6  44  50   0   0
2021 Dec 05  14 05  +26 05   0.874   0.387   94    62M  6.5  6.4  41  47   0   0
2021 Dec 06  14 21  +24 26   0.859   0.356   99    59M  6.3  6.2  38  44   0   0
2021 Dec 07  14 39  +22 20   0.846   0.326  105    55M  6.1  5.8  34  40   0   0
2021 Dec 08  14 59  +19 39   0.832   0.299  112    51M  6.0  5.6  29  35   0   0
2021 Dec 09  15 23  +16 17   0.818   0.276  119    46M  5.8  5.2  22  29   0   0
2021 Dec 10  15 49  +12 06   0.805   0.256  128    39M  5.7  4.7  15  21   0   0
2021 Dec 11  16 19  +07 08   0.792   0.242  137    32M  5.6  4.1   7  13   0   0
2021 Dec 12  16 50  +01 32   0.779   0.235  147    25M  5.6  3.4   0   4   0   0
2021 Dec 13  17 22  -04 19   0.767   0.234  155    18E  5.6  2.6   0   1   0   0
2021 Dec 14  17 55  -09 58   0.755   0.241  160    15E  5.7  2.0   0   3   0   0
2021 Dec 15  18 25  -15 01   0.743   0.254  159    15E  5.8  2.3   0   4   0   0
2021 Dec 16  18 53  -19 15   0.731   0.273  154    18E  6.0  3.1   0   5   0   0
2021 Dec 17  19 18  -22 40   0.720   0.297  147    22E  6.2  4.0   1   6   0   4
2021 Dec 18  19 39  -25 22   0.709   0.324  141    26E  6.4  4.7   2   6   1   9
2021 Dec 19  19 58  -27 28   0.699   0.354  135    29E  6.6  5.3   2   7   4  12
2021 Dec 20  20 14  -29 06   0.689   0.387  130    32E  6.9  5.8   3   7   7  15
2021 Dec 21  20 28  -30 22   0.680   0.421  125    34E  7.1  6.2   3   7  10  18
2021 Dec 22  20 40  -31 23   0.671   0.456  120    36E  7.3  6.6   3   7  11  19
2021 Dec 23  20 50  -32 12   0.663   0.492  116    37E  7.4  6.9   3   7  13  21
2021 Dec 24  20 58  -32 51   0.655   0.529  111    38E  7.6  7.2   3   7  14  22
2021 Dec 25  21 05  -33 24   0.648   0.566  107    38E  7.8  7.5   3   7  14  23
2021 Dec 26  21 12  -33 51   0.641   0.604  104    39E  7.9  7.7   3   7  15  23
2021 Dec 27  21 17  -34 13   0.636   0.642  100    39E  8.1  7.9   3   7  15  24
2021 Dec 28  21 21  -34 32   0.631   0.680   97    39E  8.2  8.1   2   6  16  24
2021 Dec 29  21 25  -34 49   0.626   0.718   93    39E  8.4  8.4   2   6  16  24
2021 Dec 30  21 29  -35 03   0.622   0.757   90    39E  8.5  8.5   2   6  16  24
2021 Dec 31  21 32  -35 15   0.620   0.795   87    38E  8.6  8.6   1   5  16  24

 

Let’s again assume a healthy normal comet for the remainder of the month, what will the tails of Leonard look like? Currently, the comet’s dust and gas tails are superimposed on each other. Using the Finson-Probstein analysis program of the Comet Toolbox (https://www.comet-toolbox.com/FP.html), we should expect that to continue for another week and a half. With the Earth crossing the comet’s orbital plane on December 8, the dust tail may become very narrow for a few days. After close approach, the dust tail should diverge from the anti-solar direction and fan out away from the gas tail.

 

One must be careful when interpreting the following figure. It only shows the possible orientation of the tails relative to the nucleus. It should not be used to infer the absolute or relative lengths of the tails. All bets are off if the comet continues to fade or even completely disrupt.

 

FinsonProbsteinforLeonard.jpg

 

Figure 4 - Finson-Probstein analysis for C/2021 A1 (Leonard) as modeled with the Comet Toolbox (https://www.comet-toolbox.com/FP.html). Synchrones are lines of constant time of dust release (in days prior to the modeled data) while syndynes are lines of constant dust size. The values of the syndynes are the “beta” of the particles which is the ratio of solar radiation pressure to solar gravity and is inversely proportional to grain size.

 

If the above image is too low resolution to read, please download the pdf version of this report from the ALPO site.

 

Here to a bunch of lost sleep this month watching C/Leonard!

 

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-W138)

 

   8P/Tuttle                                                                   
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2021 Aug. 27.73567 TT                                 Rudenko                
q   1.0259957            (2000.0)            P               Q                 
n   0.07229128     Peri.  207.48835     -0.26845021     -0.50831915            
a   5.7070558      Node   270.20165     +0.96327501     -0.13638410            
e   0.8202233      Incl.   54.91130     +0.00597787     -0.85030055            
P  13.6                                                                        
From 271 observations 2008 Feb. 12-2021 Nov. 23, mean residual 0".6.           
     Nongravitational parameters A1 = +0.01, A2 = -0.0091.

 

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 Dec 01  14 19  -49 21   1.707   2.381    37M   Lup  11.8     0   19
2021 Dec 06  14 37  -50 17   1.759   2.427    38M   Lup  12.2     0   20
2021 Dec 11  14 53  -51 04   1.810   2.470    38M   Lup  12.5     0   21
2021 Dec 16  15 10  -51 45   1.862   2.512    39M   Lup  12.8     0   21
2021 Dec 21  15 25  -52 19   1.913   2.550    40M   Lup  13.1     0   22
2021 Dec 26  15 40  -52 47   1.965   2.585    41M   Nor  13.4     0   24
2021 Dec 31  15 55  -53 11   2.016   2.616    43M   Nor  13.7     0   25
2022 Jan 05  16 08  -53 32   2.068   2.644    44M   Nor  14.0     0   27

 

Comet Magnitude Formula

 

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

 

A large geocentric distance, small solar elongation, and invisibility from the northern hemisphere have limited observations of 8P/Tuttle during the current return. Perihelion was back on 2021 August 27 with a peak brightness of 8.5-9.0 during September. Last month Chris Wyatt visually observed Tuttle on November 13 with a 0.4-m reflector at 59x. He measured a brightness of 10.4 with a weakly condensed (DC = 3) 3.5’ coma.

 

The comet will be rapidly fading in December from around magnitude ~12 to ~14 as it moves through Lupus (Dec 1-22) and Norma (22-31). As has been the case for much of this apparition, Tuttle will only be visible to southern hemisphere observers.

 

Imagers are encouraged to take deep, wide field images of Tuttle during the 2nd half of the December as the Earth will be crossing the Tuttle’s orbital plane on December 21. The dust trail consists of larger dust particles orbiting along the comet’s orbit. These particles are populating the Ursid meteor stream, so any image of Tuttle’s dust trail may be an image of future Ursids.

 

This will probably be the last month we report on 8P as it will fainter than our 13th magnitude cutoff next month. Looking towards the future, two returns from now will be much better with Tuttle passing 0.18 au from Earth on 2048 December 28 and brightening 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-W138)

 

  67P/Churyumov-Gerasimenko                                                    
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2021 Nov. 2.06613 TT                                  Rudenko                
q   1.2106365            (2000.0)            P               Q                 
n   0.15341012     Peri.   22.13772     +0.52344271     -0.85112125            
a   3.4559442      Node    36.33307     +0.77128090     +0.45334133            
e   0.6496944      Incl.    3.87158     +0.36212360     +0.26471542            
P   6.42                                                                       
From 8556 observations 1995 July 3-2021 Nov. 29, mean residual 0".8.           
     Nongravitational parameters A1 = +0.09, 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 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
2021 Dec 11  08 59  +27 15   1.304   0.438   128M   Cnc   8.3    77   20
2021 Dec 16  09 03  +27 29   1.328   0.446   132M   Cnc   8.3    77   21
2021 Dec 21  09 04  +27 46   1.354   0.454   137M   Cnc   8.4    78   22
2021 Dec 26  09 03  +28 05   1.382   0.465   142M   Cnc   8.5    78   22
2021 Dec 31  09 01  +28 23   1.412   0.479   147M   Cnc   8.6    78   22
2022 Jan 05  08 58  +28 39   1.443   0.496   153M   Cnc   8.7    79   21

 

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 at the Alma-Ata Astrophysical Institute in current day Kazakhstan. The current apparition is 67P’s 9th observed return with perihelion back 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. Though this return will be the best for the remainder of the century, it will make similar, but slightly larger, approaches to Earth in 2034 (0.45 au), 2067 (0.44 au), and 2080 (0.49 au).

 

Last month, visual observers found 67P to be between magnitude 9.0 and 9.9 (aperture corrected to 8.6 to 9.6). with up to a quarter degree of tail. The comet spends December in the morning sky in Cancer. Based on previous apparitions, 67P should be at its brightest during the first half of December at around magnitude 8.3 and slightly fade to around 8.6 by New Year’s.

 

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 Syuichi Nakano, personal email)

 

    C/2019 L3 (ATLAS)                                                          
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2022 Jan.  9.61930 TT                                 Rudenko                
q   3.5545066            (2000.0)            P               Q                 
z  -0.0004534      Peri.  171.61066     -0.26052094     -0.66630823            
 +/-0.0000003      Node   290.79019     +0.83675993     +0.20517882            
e   1.0016115      Incl.   48.36122     +0.48162398     -0.71689259            
From 2893 observations 2019 June 10-2021 Nov. 19, mean residual 0".4.          
1/a(orig) = +0.000102 AU**-1, 1/a(fut) = -0.000881 AU**-1.

 

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 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
2021 Dec 11  07 33  +36 15   3.564   2.700   146M   Lyn   9.0    86   14
2021 Dec 16  07 29  +35 33   3.561   2.661   152M   Aur   8.9    85   15
2021 Dec 21  07 24  +34 48   3.559   2.629   157M   Gem   8.9    85   15
2021 Dec 26  07 19  +33 59   3.557   2.605   162M   Gem   8.9    84   16
2021 Dec 31  07 14  +33 07   3.555   2.589   167M   Gem   8.9    83   17
2022 Jan 05  07 08  +32 12   3.554   2.581   170M   Gem   8.9    82   18

 

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-60 days]
m1 =  2.4 + 5 log d +  8.0 log r [T-60 days and onwards]

 

The next two comets also share the near-opposition sky with C/2019 L3 (ATLAS). With only a month to go till its perihelion at 3.57 au (T = 2022 January 9), ATLAS should finally reach peak brightness around magnitude 9. In November, Chris Wyatt, Carl Hergenrother, Christian Harder, and J. J. Gonzalez made 6 visual observations finding the comet between magnitude 9.5 and 10.2 (aperture corrected range of 9.2 and 9.8). Chris and Christian were also able to visually detect a tail up to 6’ in length in 0.3- to 0.4-m telescopes.

 

C/2019 L3 (ATLAS) will be approaching opposition while moving through Lynx (Dec 1-14), Auriga (14-17), and Gemini (17-31) in the morning sky. While well placed for northern observers, it is also visible but low from the southern hemisphere.

 

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-W138)

 

  19P/Borrelly                                                                 
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2022 Feb. 1.83020 TT                                  Rudenko                
q   1.3062541            (2000.0)            P               Q                 
n   0.14401007     Peri.  351.92096     +0.38674585     -0.79279248            
a   3.6047416      Node    74.24710     +0.87109441     +0.14639270            
e   0.6376289      Incl.   29.30470     +0.30269155     +0.59164961            
P   6.84                                                                       
From 480 observations 2015 Jan. 11-2021 Nov. 29, mean residual 0".7.           
     Nongravitational parameters A1 = -0.86, A2 = -0.7759.

 

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 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
2021 Dec 11  23 41  -32 12   1.447   1.173    83E   Scl   9.9    18   54
2021 Dec 16  23 49  -29 03   1.423   1.174    82E   Scl   9.7    21   49
2021 Dec 21  23 58  -25 47   1.401   1.175    80E   Scl   9.5    24   44
2021 Dec 26  00 07  -22 24   1.381   1.178    78E   Cet   9.4    27   40
2021 Dec 31  00 16  -18 56   1.363   1.183    77E   Cet   9.2    31   36
2022 Jan 05  00 26  -15 23   1.347   1.189    76E   Cet   9.1    33   32

 

Comet Magnitude Formula (from Seiichi Yoshida)

 

m1 = 5.5 + 5 log d + 25.0 log r

 

19P/Borrelly should be one of the better comets of 2022 when it may reach 9th magnitude around the time of its 2022 February 1 perihelion (at 1.31 au). Borrelly is steadily moving north and is now visible in the evening sky from both hemispheres as it moves through Grus (Dec 1), Sculptor (1-22), and Cetus (22-31). While no magnitude estimates were submitted to the ALPO for Borrelly in November, observations submitted to the COBS site place the comet around magnitude 10.5 at the end of November which is line with the prediction above. By the end of the year, the comet should be around magnitude 9.2. Images from the past week show a long dust trail located along the orbit of Borrelly. This feature should become stronger and better defined as the Earth crosses the plane of Borrelly’s orbit on December 6.

 

Comets Between Magnitude 10 and 13

 

4P/Faye

 

Discovered visually on 1843 November 23 by the Herve Faye

 

Orbit (from MPEC 2021-W138)

 

   4P/Faye                                                                     
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2021 Sept. 8.84459 TT                                 Rudenko                
q   1.6189102            (2000.0)            P               Q                 
n   0.13180036     Peri.  207.00519     +0.76775595     -0.63998354            
a   3.8240625      Node   192.93053     +0.61016079     +0.74509813            
e   0.5766517      Incl.    8.00831     +0.19558786     +0.18774941            
P   7.48                                                                       
From 5784 observations 1998 May 24-2021 Nov. 29, mean residual 0".9.           
     Nongravitational parameters A1 = +0.55, A2 = -0.0287.   

 

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 Dec 01  06 54  +07 49   1.820   0.938   142M   Mon  10.8    58   42
2021 Dec 06  06 52  +07 28   1.843   0.937   146M   Mon  10.9    57   43
2021 Dec 11  06 49  +07 14   1.866   0.940   151M   Mon  11.0    57   43
2021 Dec 16  06 45  +07 06   1.891   0.948   156M   Mon  11.2    57   43
2021 Dec 21  06 41  +07 05   1.916   0.961   160M   Mon  11.3    57   43
2021 Dec 26  06 37  +07 11   1.942   0.979   163M   Mon  11.5    57   43
2021 Dec 31  06 33  +07 22   1.968   1.003   164E   Mon  11.7    57   43
2022 Jan 05  06 29  +07 39   1.995   1.033   163E   Mon  11.9    58   42

 

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. It has never rivaled its discovery apparition in brightness and at its best only gets to 9th magnitude (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.

 

Photo Op: Dec 30-Jan 1 – 4P/Faye passes between 9th mag open cluster NGC 2254 and emission nebula IC 448.

 

6P/d’Arrest

 

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

 

Orbit (from MPEC 2021-W138)

 

   6P/d'Arrest                                                                 
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2021 Sept. 17.76118 TT                                Rudenko                
q   1.3545380            (2000.0)            P               Q                 
n   0.15067344     Peri.  178.08852     +0.73289133     +0.64399340            
a   3.4976653      Node   138.93495     -0.62855292     +0.76434200            
e   0.6127308      Incl.   19.51219     -0.26036805     -0.03246255            
P   6.54                                                                       
From 3229 observations 1987 Mar. 31-2021 Nov. 29, mean residual 1".0.          
     Nongravitational parameters A1 = +0.54, 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 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
2021 Dec 11  23 00  -25 09   1.651   1.545    78E   PsA  11.0    25   42
2021 Dec 16  23 14  -23 50   1.682   1.609    76E   Aqr  11.2    26   40
2021 Dec 21  23 28  -22 30   1.714   1.675    75E   Aqr  11.4    27   37
2021 Dec 26  23 41  -21 07   1.746   1.743    73E   Aqr  11.6    28   35
2021 Dec 31  23 54  -19 44   1.779   1.813    72E   Aqr  11.9    29   33
2022 Jan 05  00 06  -18 20   1.812   1.884    70E   Cet  12.1    29   31

 

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)

 

6P/d’Arrest is also past perihelion [T = 2021 September 17 @ 1.35 au]. Due to an asymmetrical lightcurve, the comet peaks in brightness a month or two after perihelion. December should see the comet fade from around magnitude 10.7 to 11.9 though observations in late October and early November suggest 6P may be 0.5-1.0 magnitudes brighter than the above prediction.

 

This month, 6P is an evening object moving through Pisces Austrinus (Dec 1-12), Aquarius (12-31) and Cetus (31). Though better placed for southern observers, it is observable from both hemispheres.

 

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-W138)

 

  29P/Schwassmann-Wachmann                                                     
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2019 Apr. 4.85113 TT                                  Rudenko                
q   5.7713405            (2000.0)            P               Q                 
n   0.06636470     Peri.   49.81465     +0.99174187     -0.04468182            
a   6.0419613      Node   312.38189     -0.02059024     +0.86971579            
e   0.0447902      Incl.    9.36627     +0.12658632     +0.49152618            
P  14.9                                                                        
From 11652 observations 2018 June 18-2021 Nov. 29, 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 Dec 01  04 37  +31 59   5.935   4.963   169M   Per  10-13   82   18
2021 Dec 06  04 35  +31 52   5.937   4.964   170E   Per  10-13   82   18
2021 Dec 11  04 32  +31 44   5.938   4.973   167E   Per  10-13   82   18
2021 Dec 16  04 29  +31 34   5.940   4.990   163E   Per  10-13   82   18
2021 Dec 21  04 27  +31 25   5.941   5.014   158E   Per  10-13   81   19
2021 Dec 26  04 24  +31 14   5.943   5.045   153E   Per  10-13   81   19
2021 Dec 31  04 22  +31 03   5.944   5.084   148E   Per  10-13   81   19
2022 Jan 05  04 20  +30 52   5.946   5.129   143E   Tau  10-13   81   19

 

29P/Schwassmann-Wachmann was discovered photographically on 1927 November 15 by German observing team Arnold Schwassmann and Arno Arthur Wachmann. 29P is one of the more enigmatic comets as it experiences outbursts multiple times per year that can reach 10-14th magnitude.

 

29P has been especially active of late with multiple outbursts observed since late September. As a result, the comet is about as bright as it ever gets with many visual observers reporting the comet to be between magnitude 10.0 and 11.4 with a coma diameter between ~2-5’.

 

The comet is at opposition on December 2 in Perseus 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.ast...P/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-W138)

 

  57P/du Toit-Neujmin-Delporte                                                 
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2021 Oct. 17.39693 TT                                 Rudenko                
q   1.7200339            (2000.0)            P               Q                 
n   0.15397450     Peri.  115.25496     +0.55935853     +0.82889115            
a   3.4474940      Node   188.76828     -0.77729950     +0.52132122            
e   0.5010770      Incl.    2.85132     -0.28796444     +0.20288827            
P   6.40                                                                       
From 1126 observations 2015 Feb. 18-2021 Nov. 29, mean residual 0".7.    

                                                                               

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 Dec 01  20 12  -18 24   1.769   2.187    52E   Cap  11-13   21   17 
2021 Dec 06  20 26  -17 44   1.780   2.231    50E   Cap  11-13   21   14
2021 Dec 11  20 40  -17 00   1.792   2.276    49E   Cap  11-13   21   11
2021 Dec 16  20 53  -16 12   1.806   2.321    47E   Cap  11-13   21    8
2021 Dec 21  21 07  -15 21   1.820   2.367    45E   Cap  11-13   20    6
2021 Dec 26  21 20  -14 28   1.835   2.414    43E   Aqr  11-13   20    4
2021 Dec 31  21 33  -13 31   1.851   2.461    41E   Cap  11-13   19    2
2022 Jan 05  21 46  -12 32   1.868   2.509    40E   Cap  11-13   18    0

 

 

Daniel du Toit was the first to discover 57P/du Toit-Neujmin-Delporte 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. 57P 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 it was observed 5 magnitudes brighter at 11th magnitude.

 

While not as outburst prone as 29P, 57P experienced a 6-magnitude outburst in 1996 which may have produced 19 or more secondary nuclei that were observed during its next return in 2002. Its abnormal brightness in 1941 also suggests an outburst in that year.

 

While observations to the ALPO and COBS have been few in November, they do suggest the comet is still as bright as magnitude 11.0 on November 9 (Uwe Pilz) and 11.7 on November 24 (Steffen Fritsche to COBS). December sees 57P as an evening object in Capricornus (Dec 1-25), Aquarius (25-28), and Capricornus (28-31). Unless another outburst occurs, 57P should 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-U138)

 

    C/2017 K2 (PANSTARRS)                                                      
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5                                        
T 2022 Dec. 19.69196 TT                                 Rudenko                
q   1.7971155            (2000.0)            P               Q                 
z  -0.0003894      Peri.  236.19330     +0.01825440     +0.04925462            
 +/-0.0000008      Node    88.23673     -0.18101700     +0.98244314            
e   1.0006999      Incl.   87.55886     -0.98331054     -0.17994295            
From 7072 observations 2013 May 12-2021 Nov. 22, mean residual 0".4. 
1/a(orig) = -0.000031 AU**-1, 1/a(fut) = +0.001161 AU**-1.

 

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 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
2021 Dec 11  17 41  +15 11   4.582   5.308    38E   Her  11.5    12    0
2021 Dec 16  17 45  +14 40   4.538   5.272    38E   Her  11.5     9    0
2021 Dec 21  17 49  +14 12   4.494   5.232    37M   Oph  11.4     8    0
2021 Dec 26  17 53  +13 46   4.449   5.187    37M   Oph  11.4    11    0
2021 Dec 31  17 57  +13 22   4.405   5.138    37M   Oph  11.3    14    0
2022 Jan 05  18 01  +13 00   4.360   5.084    38M   Oph  11.2    17    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.

 

C/2017 K2 is poorly placed for observation this month as it passes through solar conjunction, though it will be ~37 degrees north of the Sun at conjunction. As a result, it will be invisible to southern hemisphere observers but visible at low elevations from the northern hemisphere (moving through Hercules [Dec 1-20] and Ophiuchus [20-31]. Northern observers with a clear and dark northern horizon should be able to watch K2 brighten from around magnitude 11.6 to 11.2 this month.

 

The comet will reappear for southern hemisphere observers in 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 won’t see the comet again till August 2023 when it will have faded to around magnitude 10.0.

 

Like 8P/Tuttle, 19P/Borrelly, and C/2021 A1 (Leonard), C/2017 K2 will also have an orbit plane crossing this month (on December 19). While first time Oort Cloud comets usually have yet to release enough dust to produce dust trails before perihelion, K2 has been active out to 23 au and possible further. Imagers should attempt to image any dust trail in mid-December since the existence and morphology of a trail may provide additional constraints on the start of K2’s activity.

 

New Discoveries, Recoveries and Other Comets News

 

New Comet Numberings (Ref: WGSBN Bull. 1 #12)

 

436P/2007 R4   = 2021 U2 (Garradd)

435P/2021 T3   = 2015 K6 (PANSTARRS)
434P/2012 TK8  = 2021 S2 (Tenagra)
433P = (248370) Dual status
432P/2021 N4   = P/2016 U2 (PANSTARRS)
431P/2015 Q1   = P/2021 P5 (Scotti)
430P/2011 A2   = P/2021 Q2 (Scotti)
429P/2008 QP20 = P/2021 M1 (LINEAR-Hill)
428P/2014 W12  = P/2021 Q1 (Gibbs)
427P/2017 S5   = P/2021 L6 (ATLAS)
426P/2019 A7   = P/2021 K4 (PANSTARRS)

 

New Comet Discoveries
P/2021 V3 = P/2011 UE215 (PANSTARRS) – Discovered by the Pan-STARRS survey at 21st magnitude with the Pan-STARRS1 1.8-m on 2021 November 1. After additional observations in 2021 were found, the Minor Planet Center linked the new comet with observations in 2012 and a designated object from 2011 called 2011 UE215. Perihelion will be on 2022 August 18 at 3.40 au. According to Syuichi Nakano, the comet passed 0.39 au from Jupiter in 2007. Prior to the 2007 encounter, its perihelion was larger at 3.95 au. P/2021 V3 is unlikely to get brighter at this return. [CBET 5069, MPEC 2021-V173]

 

P/2021 V2 (Fuls) – Discovered by David Carson Fuls at 19th magnitude with the Mount Lemmon 1.5-m on 2021 November 7. This comet is a short-period comet with an orbital period of 27.2 years. Perihelion is on 2023 January 21 at 3.50 au. Perihelion will be next year on 2022 April 30 at 3.01 au with a peak brightness of 17th magnitude. [CBET 5068, MPEC 2021-V169]

 

C/2021 V1 (Rankin) – Discovered by David Rankin at 20th magnitude with the Mount Lemmon 1.5-m on 2021 November 5. Perihelion will be next year on 2022 April 30 at 3.01 au. The comet is unlikely to get brighter than 19th magnitude.[CBET 5067, MPEC 2021-V167]

 

C/2021 U5 (Catalina) – The Catalina Sky Survey found yet another comet. This time it was Alex Gibbs who used the Catalina 0.68-m Schmidt to find this 18th magnitude comet on October 29. Perihelion will be next month on 2022 January 25 at 2.37 au. It should peak in brightness next February and March at ~17th magnitude. [CBET 5070, MPEC 2021-V199]

 

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!

 

Clear skies!
- Carl Hergenrother

 


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#2 happylimpet

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Posted 03 December 2021 - 08:48 AM

Thanks Carl, hugely appreciated as ever.



#3 Carl H.

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Posted 03 December 2021 - 08:01 PM

Thanks Carl, hugely appreciated as ever.

Thanks for the kind words.

 

I hope I wasn't too pessimistic about Leonard's prospects. I've gone back and forth so many times over the past few weeks about this comet.


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#4 Zorbathegeek

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Posted 04 December 2021 - 05:12 AM

I, for one, really appreciated the extensive analysis of Leonard and its prospects. Sitting patiently here in NZ, I'll be very happy if it doesn't burn out before it reaches our hemisphere and even happier if it's as bright as 5th magnitude when it appears in our skies. 

 

Ray.



#5 SNH

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Posted 04 December 2021 - 08:12 PM

"Here to a bunch of lost sleep this month watching C/Leonard!"

 

Aye, aye, Capt'n! Got to see it on the morning of the 3rd "below" M3. Breathtaking! Could even barely see it naked-eye at the start of astronomical twilight under 21.2 mpsas skies. Hope it gets to be an easier naked-eye comet so others can see it that way, too.

 

Scott

 

P.S. Great reporting there, Carl! Really enjoyed your synopsis on Leonard.



#6 Aquarellia

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Posted 05 December 2021 - 01:41 AM

What an interesting article !  

As always we are waiting for your monthly comet news and there's always something new to learn.

Thank you Carl for sharing that with all of us !

Michel


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#7 Carl H.

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Posted 06 December 2021 - 08:13 PM

I've finally set up my imaging rig and have been observing Leonard in a Green and Red filter for photometry and morphology studies.
 
http://www.alpo-astr...rl-Hergenrother
 
Even in a small 72mm AT72EDII, I can see two "jets" extending perpendicular to the solar direction. This feature has been seen in other's images for some time now. As you can see in the image below, this feature appears to only consist of gas and not dust since it is not visible in Red images. 
 
http://www.alpo-astr...rl-Hergenrother
 
As for photometry, here are my latest visual and CMOS observations:
 
2021 Dec. 06.53, 5.7, 30.7' (C. Hergenrother, 0.072-m refractor + CMOS; >1.35-deg tail in p.a. 321)
2021 Dec. 06.47, 6.0, 10'   (C. Hergenrother, 10x50 binoculars; 1.0-deg tail in p.a. 320)
2021 Dec. 05.53, 6.0, 28.1' (C. Hergenrother, 0.072-m refractor 
+ CMOS; >1.5-deg tail in p.a. 321)
2021 Dec. 05.47, 6.3, 7'    (C. Hergenrother, 10x50 binoculars; 0.5-deg tail in p.a. 320)
2021 Dec. 02.49, 6.5, 26.3' (C. Hergenrother, 0.072-m refractor 
+ CMOS; >1.0-deg tail in p.a. 317)
2021 Dec. 02.48, 6.7, 8'    (C. Hergenrother, 10x50 binoculars; 0.7-deg tail in p.a. 320)
2021 Dec. 01.51, 7.0, 6'    (C. Hergenrother, 10x50 binoculars; 0.3-deg tail in p.a. 320)
2021 Dec. 01.51, 6.6, 26.3' (C. Hergenrother, 0.072-m refractor 
+ CMOS; >1.3-deg tail in p.a. 316)
2021 Nov. 30.47, 7.1, 5'    (C. Hergenrother, 10x50 binoculars; 0.3-deg tail in p.a. 320)
2021 Nov. 28.50, 7.2, 7'    (C. Hergenrother, 10x50 binoculars; 0.2-deg tail in p.a. 315)

 
The imaging data is detecting a much larger coma than what I can see visually which probably also explains why the imaging photometry is brighter than the visual. I failed to see Leonard in my 2.3x42 mm (really a ~15mm aperture) binoculars on Dec. 5 UT.


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#8 Carl H.

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Posted 09 December 2021 - 03:23 PM

After a few mornings plagued by cirrus, I was able to observe and image C/2021 A1 (Leonard) once again. 

 

Dec. 09.53, 5.4, 29.8' (C. Hergenrother, 0.072-m R + CMOS; >1.4-deg tail in p.a. 327)

Dec. 09.50, 5.0, 12'   (C. Hergenrother, 10x50 B; 1.5-deg tail in p.a. 325)

 

This morning's images can be found at the ALPO Comets Section image gallery:

 

http://www.alpo-astr...-Hergenrother-2

 

http://www.alpo-astr...-Hergenrother-1

 

The two "jets" perpendicular to the solar vector are still visible in the Green images though much fainter than a few nights ago. Two tails appear in both the Green and Red images as we have a bit of separation between gas and dust tails.

 

This may be the end of my morning imaging of Leonard as tonight brings clouds and rain and after that the comet will be too low. Hopefully I'll get at least one more morning shot at Leonard visually. I should be able to image and observe the comet again when it reappears in the evening sky.


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#9 Carl H.

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Posted 11 December 2021 - 04:43 PM

Visual observations from this morning:

 

Dec. 11.54, 4.8, 7'   (C. Hergenrother, 10x50 B; 0.7-deg tail in p.a. 330)

 

This is probably my last morning observation.


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#10 emh52

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Posted 12 December 2021 - 02:22 PM

With Leonard out of sight, caught Atlas that is well placed and close to its brightest presentation before the Moon gets in the way, this is 7 x 90 sec stacked from iTelescope T02

full resolution: https://flic.kr/p/2mQgBfA  

Attached Thumbnails

  • CN atlas.jpg

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#11 Carl H.

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Posted 15 December 2021 - 12:29 PM

Evening observations of Leonard have started to come in and suggest the comet is brighter than when we last saw it in the morning sky. Back on the 11th, Leonard was around magnitude 5.0 or a little brighter. Observations from the past day or so estimate it to be around magnitude 2.6 to 3.2. 

 

Here are a few postings on comets-ml and comets-images that contain images.

 

https://groups.io/g/...l/message/30302

https://groups.io/g/...l/message/30303

https://groups.io/g/...es/message/1954

 

While it is possible Leonard has experienced an outburst (conveniently when not visible from Earth), its current brightness is also consistent with dust forward scattering. If the increased brightness is due to forward scattering, the comet should rapidly fade by almost a magnitude per day as its phase angle decreases.


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#12 Carl H.

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Posted 17 December 2021 - 06:14 PM

I'm changing my mind on Leonard's possible outburst. While some of its enhanced brightness is probably due to dust forward scattering, I believe that a significant outburst has also occurred. 

 

Evidence supporting an outburst include:

- Recent images showing the telltale sign of a recent outburst (see Mike Olason's image from Dec 17). The coma morphology looks very similar to other outbursting comets such as 15P/Finlay in mid-late January 2015, 332P/Ikeya-Murakami in November 2010, and C/2012 X1 (LINEAR) in Oct/Nov 2013, to name a few.

- Radio observations of OH radical from the Nançay radio telescope posted by Nicolas Biver on comets-ml. The Nançay observations show Leonard's gas production rate increasing by ~3X between Dec 13 and 15.

- Observations made by the STEREO-A spacecraft posted by Karl Battams on comets-ml. STEREO-A is located around 1 au from the Sun but trails the Earth by about ~35 deg. (See its exact position here.)

 

I was finally able to observe Leonard again last evening. Here are some observations submitted to the ALPO over the past 24 hours.

 

Dec. 17.75, 4.3, 5'  (J. Gonzalez Suarez, Sierra del Aramo, Spain, 10x50 binoculars)
Dec. 17.43, 4.9, 14' (C. Wyatt, 15x70 binoculars)
Dec. 17.41, 5.0, 16' (C. Wyatt, 0.25-m Newtonian reflector; 16.0' tail in p.a. 90)
Dec. 17.06, 4.1, 5'  (C. Hergenrother, 10x50 binoculars)
Dec. 17.05, 4.3, 11' (C. Hergenrother, 0.072-m refractor; 0.12-deg tail in p.a. 75)


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#13 Zorbathegeek

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Posted 19 December 2021 - 05:11 AM

The current La Nina has made astronomy very difficult indeed over the past three months, from my part of New Zealand's South Island. Today, however, it cleared up, and I got to see C/2021 A1 Leonard. I observed it from a reasonably dark park in the city centre, using 20x80 binoculars, and was very happy to find that the outburst, that Carl mentioned, is still ongoing. The comet was around 4.8 magnitude and was easy to locate due to its proximity to c Sgr. The observation was at 10.40pm local time, whilst the comet was a little under 10 degrees altitude. The universal coordinated time was 9.40am, Sunday 19th.

 

Ray.


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#14 Carl H.

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Posted 20 December 2021 - 12:03 PM

Leonard appeared even brighter last night from Tucson.

 

C/2021 A1 (Leonard)
2021 Dec
20.06, 3.5, 6’ (Carl Hergenrother, Tucson, AZ, U.S.A., 10x50 binoculars);
19.06, 4.0, 7’ (Carl Hergenrother, Tucson, AZ, U.S.A., 10x50 binoculars);
17.06, 4.1, 5’ (Carl Hergenrother, Tucson, AZ, U.S.A., 10x50 binoculars);

 

On Sat evening, I was able to take 20 second subframes of Leonard in Green and Red filter without saturation. Last evening I was down to only 3 seconds! 

 

Visually the comet appeared much more condensed with an almost stellar central condensation.


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#15 SNH

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Posted 21 December 2021 - 08:10 PM

My first clear night to see the comet was on the evening of the 19th (0 hours UTC on 20th). I blew it by going to the new Marvel movie in theaters.

 

So tonight I FINALLY got to get my first look at Leonard post-perihelion. It first caught site of it 50 minutes after sunset in 10x50 binoculars. I was able to glimpse it naked-eye 75 minutes after sunset. The comet reminded my of 2013's appearance of L4 PanSTARRS -- albeit fainter. But not too faint. I estimated it at about magnitude +4.1 with possibly a 1 degree long tail sliding to the upper left in binoculars. The coma is smaller than was visible back in the morning sky with a very condensed star-like nucleus.

 

Scott




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