ALPO COMET NEWS FOR OCTOBER 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
Magnitude 9 to 10 may not be everyone’s idea of “bright” when it comes to comets. After months of no comets getting brighter than 10th magnitude, we finally have a few objects breaking the 10th magnitude barrier. The target of the European Space Agency’s Rosetta mission, 67P/Churyumov-Gerasimenko may brighten to around magnitude 9 this month. It will be observable from both hemispheres in the morning sky. 8P/Tuttle will start the month around 8-9th magnitude but is limited to southern hemisphere observers. C/2019 L3 (PANSTARRS) could become brighter than magnitude 10 though it will mainly be a northern object.
29P/Schwassmann-Wachmann experienced 4 outbursts in quick succession in late September. As a result, it is brighter than it has become in years with visual observers placing it between magnitude 10 and 11.
We continue to watch C/2021 A1 (Leonard) develop as it heads towards a December encounter with Earth. Recent observations show a rapid brightening trend, so imagers and large aperture visual observers are encouraged to observe it this month as it may brighten to magnitude 11 by the end of the month.
Comets Section News
During September, the ALPO Comets Section received 51 images and/or sketches from Dan Bartlett, Denis Buczynski, Eliot Herman, Gianluca Masi, Martin Mobberley, Uwe Pilz, Efrain Morales Rivera, Gregg Ruppel, and Chris Schur and 67 visual and CCD magnitude measurements from Michel Deconinck, J. J. Gonzalez, Mike Olason, and Chris Wyatt of the following comets: P/2021 Q5 (ATLAS), C/2021 O3 (PANSTARRS), C/2021 A1 (Leonard), C/2020 T2 (Palomar), C/2020 PV6 (PANSTARRS), C/2020 F5 (MASTER), C/2019 O3 (PANSTARRS), C/2019 L3 (ATLAS), C/2019 F1 (ATLAS-Africano), C/2018 U1 (Lemmon), C/2020 T2 (PANSTARRS), C/2017 K2 (PANSTARRS), 284P/McNaught, 193P/LINEAR-NEAT, 106P/Schuster, 67P/Churyumov-Gerasimenko, 29P/Schwassmann-Wachmann, 19P/Borrelly, 15P/Finlay, 8P/Tuttle, 7P/Pons-Winnecke, 6P/d’Arrest, and 4P/Faye.
We’ve tried to include lightcurves for most of the objects discussed in this report as well as applying aperture corrections to the visual observations (see the PDF version for the lightcurves). 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 determing individual corrections for each observer for each individual comet as well as for digital observations.
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.
Comets Calendar for October 2021
Oct 01 – C/2020 H6 (ATLAS) at perihelion (q = 4.70 au, long-period, V~13-14)
Oct 02-09 – C/2020 T2 (Palomar) passes in front of the large area of nebulosity near Antares and rho Oph
Oct 03-05 – 4P/Faye passes in front of Sh2-261 emission nebula
Oct 05 – 52P/Harrington-Abell at perihelion (q = 1.78 au, 7.6-year orbit, V~16)
Oct 06 – New Moon
Oct 12 – First Quarter Moon
Oct 15 – 6P/d’Arrest passes within 10’ of bright globular cluster M55
Oct 15-16 – 67P/Churyumov-Gerasimenko passes within 15’ of bright open cluster M35
Oct 17 – 57P/du Toit-Neujmin-Delporte at perihelion (q = 1.72 au, 6.4-year orbit, V ~ 15-16)
Oct 17 – 418P/LINEAR at perihelion (q = 1.70 au, 11.4-year orbit, V ~ 16-17)
Oct 18 – 110P/Hartley at perihelion (q = 2.46 au, 6.8-year orbit, V ~ 15-16)
Oct 18 – C/2021 G3 (PANSTARRS) at perihelion (q = 5.18 au, long-period, V ~ 21)
Oct 19 – 342P/SOHO at perihelion (q = 0.05 au, 5.3-year orbit, may be visible in SOHO data at perihelion)
Oct 20 – Full Moon
Oct 21 – P/2012 TK8 (Tenagra) at perihelion (q = 3.00 au, 8.4-year orbit, not seen since discovery apparition in 2012/2013 when it peaked at V ~19)
Oct 27 – 419P/PANSTARRS at perihelion (q = 2.54 au, 6.6-year orbit, V ~ 19-20)
Oct 27 – C/2020 T2 (Palomar) passes within 20-25’ of 9th mag globular cluster NGC 6304
Oct 28 – Last Quarter Moon
Oct 29 – 6P/d’Arrest passes within 10’ of 11th mag galaxy NGC 6925
Oct 31 – 424P/La Sagra at perihelion (q = 1.36 au, 9.3-year orbit, V ~ 17-18)
Comets Brighter Than Magnitude 10
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-S45)
8P/Tuttle
Epoch 2021 July 5.0 TT = JDT 2459400.5
T 2021 Aug. 27.73743 TT Rudenko
q 1.0260106 (2000.0) P Q
n 0.07228558 Peri. 207.48894 -0.26849292 -0.50829781
a 5.7073554 Node 270.20405 +0.96326319 -0.13641373
e 0.8202301 Incl. 54.91123 +0.00596493 -0.85030855
P 13.6
From 231 observations 2008 Feb. 12-2021 Sept. 16, mean residual 0".5.
Nongravitational parameters A1 = +0.40, A2 = +0.2133.
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-Oct-01 10 36 -21 40 1.150 1.852 33M Hya 8.6 0 15
2021-Oct-06 10 53 -25 14 1.186 1.878 33M Hya 8.8 0 16
2021-Oct-11 11 11 -28 35 1.224 1.910 34M Hya 9.0 0 16
2021-Oct-16 11 29 -31 42 1.265 1.946 34M Hya 9.2 0 17
2021-Oct-21 11 48 -34 34 1.308 1.986 35M Hya 9.5 0 17
2021-Oct-26 12 06 -37 12 1.353 2.030 35M Cen 9.8 0 18
2021-Oct-31 12 25 -39 34 1.399 2.076 35M Cen 10.1 0 18
2021-Nov-05 12 44 -41 42 1.447 2.124 36M Cen 10.4 0 18
Comet Magnitude Formula
m1 = 7.0 + 5 log d + 20 log r(t-25) [Ref: Seiichi Yoshida]
There is not too much new to report regarding 8P/Tuttle this month. The current return is limited to observers in the southern hemisphere and even there it is a low morning object as it moves through Hydra (Oct 1-23) and Centaurus (23-31). Chris Wyatt visually observed Tuttle on September 7 and 11 from Australia at magnitude 9.0 and 8.9, respectively. Chris used a 0.4-m telescope reflector, meaning with a nominal aperture correction, Tuttle may be ~0.6 magnitudes brighter than Chris’ report. Now over a month after its August 27 perihelion at 1.03 au, Tuttle should be fading this month from around magnitude 8.5 to 10.0.
Tuttle was discovered during two widely separated apparitions. Pierre François André Méchain made the first discovery on 1790 January 9. Sixty-eight years and 5 orbits later, 8P was re-discovered by Horace Parnell Tuttle on 1858 January 5. With a 13.6-year period, 8P/Tuttle is making its 13th observed return and 18th return going back to the initial 1790 discovery apparition. Tuttle’s relatively large semi-major axis of 5.7 au and inclination of 54.9° makes it a Halley-type rather than a Jupiter-family comet. Its orbit currently passes 0.096 au from Earth and a relatively safe 0.74 au from Jupiter.
The comet’s best observed apparitions occurred in 1980/1981 when it reached 6th magnitude and at its previous return in 2007/2008 when it passed 0.25 au from Earth and reached 5th magnitude. This year’s return is rather poor with a minimum Earth-comet distance of 1.81 au (last month on September 12). The next return in 2035 will be slightly better with a marginally closer Earth-comet distance of 1.54 au. Tuttle should put on a nice show 27 years (or 2 orbits) from now when it will pass within 0.18 au of Earth on 2048 December 28 and brighten to 4th magnitude.
Comet Fun Fact: Tuttle has one of the few nuclei to be detected by Earth-based radar. The now defunct Arecibo radio telescope observed the Tuttle’s nucleus in 2007-2008. It found a contact binary shape rotating with a 11.4-hr period. The larger lobe has dimensions of 5.8x4.1 km with the smaller having dimensions of 4.3x3.3 km. [Ref: John K. Harmon et al., Radar observations of 8P/Tuttle: A contact-binary comet, Icarus, Vol. 207, Issue 1, 2010, Pages 499-502, https://doi.org/10.1...rus.2009.12.026.]
67P/Churyumov-Gerasimenko
Discovered 1969 September 11 by the Klim Ivanovic Churyumov and Svetlana Ivanovna Gerasimenko
Orbit (from Minor Planet Center, MPEC 2021-S45)
67P/Churyumov-Gerasimenko
Epoch 2021 July 5.0 TT = JDT 2459400.5
T 2021 Nov. 2.05205 TT Rudenko
q 1.2106427 (2000.0) P Q
n 0.15333185 Peri. 22.12292 +0.52361232 -0.85101687
a 3.4571201 Node 36.33644 +0.77119272 +0.45349613
e 0.6498118 Incl. 3.87136 +0.36206620 +0.26478586
P 6.43
From 7400 observations 1995 July 3-2021 Sept. 18, mean residual 0".7.
Nongravitational parameters A1 = +0.07, A2 = +0.0108.
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-Oct-01 04 59 +21 27 1.274 0.500 111M Tau 9.8 72 28
2021-Oct-06 05 22 +22 38 1.256 0.479 111M Tau 9.6 73 27
2021-Oct-11 05 45 +23 40 1.241 0.462 110M Tau 9.5 74 25
2021-Oct-16 06 08 +24 33 1.228 0.448 110M Gem 9.3 75 24
2021-Oct-21 06 31 +25 15 1.219 0.437 110M Gem 9.2 75 23
2021-Oct-26 06 53 +25 48 1.213 0.429 110M Gem 9.1 76 22
2021-Oct-31 07 14 +26 11 1.210 0.424 110M Gem 9.1 76 21
2021-Nov-05 07 34 +26 26 1.210 0.421 111M Gem 9.1 76 20
Comet Magnitude Formula (modified from Seiichi Yoshida, H value brighter by 0.6 mag) & Lightcurve
m1 = 8.9 + 5 log d + 14.0 log r(t-40)
While 8P/Tuttle is limited to southern observers, 67P/Churyumov-Gerasimenko is better placed for observers in both hemispheres. Last month visual observations were submitted by J. J. Gonzalez, Christian Harder, Uwe Pilz, and Chris Wyatt who all found the comet to be as bright as magnitude 10.8 and as faint as 12.4. After applying aperture and bias corrections, the magnitude range tightened slightly to between 10.5 and 11.8. As is the case with many short-period comets, 67P experiences a seasonal bias in activity resulting in peak activity occurring weeks after perihelion. As a result, maximum brightness may not occur till December. This month should see 67P break magnitude 10.0 and could be close to magnitude 9.0 by the end of the month as its moves through Taurus (Oct 1-14) and Gemini (14-31) in the morning sky.
Orbit plane crossing happens on October 29. As we approach the end of the month, imagers are encouraged to be on the lookout for a strong dust trail along the comet’s orbit.
67P was discovered on photographic plates taken on 1969 September 11 by Kiev University Astronomical Observatory astronomers Klim Ivanovic Churyumov and Svetlana Ivanovna Gerasimenko working with a 50-cm Maksutov astrograph at the Alma-Ata Astrophysical Institute in current day Kazakhstan. The current apparition is 67P’s 9th observed return with perihelion occurring on 2021 November 2 at 1.21 au. A close approach to Earth at 0.42 au on November 12 makes this the comet’s best return since 1982 when it came marginally closer to Earth at 0.39 au. At that return, a peak brightness of 9th magnitude was reached. 67P was famously the target of the ESA Rosetta/Philae mission, the only spacecraft to have orbited and landed on a comet. This is 67P’s first return since Rosetta ended its mission by soft landing onto the comet’s surface.
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, Nakano Note NK 4342)
C/2019 L3 (ATLAS)
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5
T 2022 Jan. 9.61848 TT Nakano
q 3.5544913 (2000.0) P Q
z -0.0004539 Peri. 171.61068 -0.26052581 -0.66630775
+/-0.0000010 Node 290.79047 +0.83675882 +0.20517556
e 1.0016135 Incl. 48.36122 +0.48162328 -0.71689398
From 1281 observations 2019 June 10-2021 Jan. 4, mean residual 0".36.
(1/a)org.= +0.000021, (1/a)fut.= -0.000735 (+/-0.000001), Q= 8.
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-Oct-01 07 30 +43 07 3.671 3.692 80M Aur 10.2 63 0
2021-Oct-06 07 34 +42 42 3.660 3.613 84M Lyn 10.1 67 0
2021-Oct-11 07 37 +42 17 3.649 3.533 88M Lyn 10.0 71 1
2021-Oct-16 07 40 +41 52 3.639 3.454 92M Lyn 10.0 75 2
2021-Oct-21 07 43 +41 27 3.630 3.374 96M Lyn 9.9 79 3
2021-Oct-26 07 45 +41 01 3.621 3.296 101M Lyn 9.9 83 4
2021-Oct-31 07 46 +40 35 3.612 3.218 105M Lyn 9.8 88 5
2021-Nov-05 07 47 +40 08 3.604 3.142 110M Lyn 9.7 90 6
Comet Magnitude Formula and Lightcurve (from ALPO and COBS data)
m1 = 2.0 + 5 log d + 12.3 log r [through T-550 days; T = date of perihelion]
m1 = -4.6 + 5 log d + 20.8 log r [T-550 to T-150 days]
m1 = 2.8 + 5 log d + 8.0 log r [T-150 days and onwards]
C/2019 L3 (ATLAS) is a far northern object in Auriga (Oct 1) and Lynx (Oct 1-31) in the morning sky. Though well placed for northern observers, folks in the southern hemisphere may get their first look at the comet this month though it will never be far from the horizon in a dark sky until later in the year. Seven measurements were submitted to the ALPO from J. J. Gonzalez, Christian Harder, and Uwe Pilz. Observations taken during the 2nd half of the month found the comet between magnitude 10.5 and 11.3 (aperture corrected magnitude range from 9.6 to 10.3) with a coma between 1.4’ and 5’ in diameter.
C/2019 L3 is still three months from its 2022 January 9 perihelion at 3.57 au. The large perihelion distance means C/2019 L3 should remain a visual object well into 2022 and possibly even 2023. The comet has been brightening at rapid rate since discovery. If we assume a slow down to a more conservative 2.5n = 8 brightening rate from now till perihelion, it could brighten to between magnitude 9.0 and 9.5 between December and February.
Comets Between Magnitude 10 and 13
C/2020 T2 (Palomar)
Discovered 2020 October 7 at 19th magnitude by the Zwicky Transient Facility (ZTF)
Discovery Telescope: 1.2-m Samuel Oschin Schmidt on Mount Palomar
Dynamically old long-period comet with orbital period of 5560 years
Orbit (from Syuichi Nakano, Nakano Note NK 4449)
C/2020 T2 (Palomar)
Epoch 2021 July 5.0 TT = JDT 2459400.5
T 2021 July 11.14758 TT Nakano
q 2.0546863 (2000.0) P Q
z +0.0032038 Peri. 150.38316 -0.53887199 +0.70302914
+/-0.0000009 Node 83.04827 -0.83514131 -0.37375209
e 0.9934172 Incl. 27.87301 -0.11025416 -0.60502843
From 682 observations 2019 Dec. 11-2021 Apr. 2, mean residual 0".37.
(1/a)org.= +0.002916, (1/a)fut.= +0.003827 (+/-0.000001), Q= 8.
The comet will pass 3.10 AU from Jupiter on 2022 June 7 UT.
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)
C/2020 T2 (Palomar) Max El
(deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Oct-01 16 17 -23 59 2.272 2.622 58E Sco 10.8 9 39
2021-Oct-06 16 27 -25 07 2.298 2.692 56E Sco 11.0 8 36
2021-Oct-11 16 38 -26 10 2.324 2.763 54E Sco 11.1 7 34
2021-Oct-16 16 49 -27 08 2.352 2.833 51E Sco 11.3 6 32
2021-Oct-21 17 00 -28 01 2.381 2.904 49E Oph 11.4 5 29
2021-Oct-26 17 11 -28 50 2.410 2.975 47E Oph 11.6 4 26
2021-Oct-31 17 22 -29 34 2.441 3.045 44E Oph 11.7 4 24
2021-Nov-05 17 33 -30 13 2.472 3.114 42E Sco 11.9 3 21
Comet Magnitude Formula (from fit to ALPO and COBS data)
m1 = 0.6 + 5 log d +24.7 log r(t-34)
C/2020 T2 (PANSTARRS) peaked between magnitude 9.5 and 10.0 brightness in July. Though some months after perihelion, it has only faded by a magnitude or two. Chris Wyatt visually observed PANSTARRS on September 6 and 8 at magnitude 10.9 on both dates. Aperture correction yielded a brightness of 10.4 on the 6th and 10.1 on the 8th. The different amount of aperture correction was due to Chris using a 0.25-m (10”) reflector on one night and a 0.40-m (16”) on another. The larger aperture instrument requiring a larger aperture correction. Both observations found a moderately condensed (DC = 5-6) 3.7’ to 3.9’ coma. Michael Lehmann reported an imaging observation to the COBS site on September 15th which found the comet at magnitude 10.9 with a 7.5’ coma.
C/2020 T2 should fade by another magnitude during October. Due to the comet’s location in Scorpius (Oct 1-17) and Ophiuchus (17-31), it will be well-placed for southern hemisphere observers, but a rather low object for northern observers.
Photo Op Alert: C/2020 T2 will pass in front of the photogenic nebulosity of the Antares/Rho Ophiuchi area during the first week of October. Later in the month on the 27th, it will pass within 20-25’ of 9th mag globular cluster NGC 6304.
4P/Faye
Discovered visually on 1843 November 23 by the Herve Faye
Orbit (from Syuichi Nakano, Nakano Note NK 4500)
4P/Faye
Epoch 2021 Sept. 23.0 TT = JDT 2459480.5
T 2021 Sept. 8.83079 TT Nakano
q 1.6188553 (2000.0) P Q
n 0.13183220 Peri. 206.99673 +0.76783984 -0.63988277
a 3.8234467 Node 192.93148 +0.61006246 +0.74517843
e 0.5765979 Incl. 8.00830 +0.19556526 +0.18777418
P 7.48
From 4264 observations 2006 Aug.-2021, mean residual 0".76.
Nongravitational parameters A1 = +0.64 +/- 0.01, A2 = -0.0389 +/- 0.0003.
The comet has passed 0.63 AU from Jupiter on 2018 Mar. 7 UT.
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-Sep-01 04 48 +18 49 1.621 1.352 85M Tau 10.8 54 29
2021-Sep-06 05 01 +18 36 1.619 1.318 87M Tau 10.7 56 29
2021-Sep-11 05 14 +18 17 1.619 1.285 89M Tau 10.7 58 29
2021-Sep-16 05 26 +17 54 1.620 1.254 90M Tau 10.6 60 29
2021-Sep-21 05 38 +17 25 1.623 1.224 93M Tau 10.6 61 30
2021-Sep-26 05 49 +16 52 1.628 1.194 95M Ori 10.6 62 30
2021-Oct-01 06 00 +16 14 1.634 1.166 97M Ori 10.6 63 31
2021-Oct-06 06 10 +15 34 1.642 1.139 100M Ori 10.6 64 32
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. Since then, it has only peaked at 9th magnitude even during its best returns (as in 1991 and 2006).
This year’s apparition is Faye’s 22nd observed return with the comet having been missed at its 1903 and 1918 returns. 2021 is a moderately good, but not great, apparition with perihelion on 2021 September 8 at 1.62 au. October should see Faye at its brightest at around magnitude 10.6. 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.
Visual observations submitted by J. J. Gonzalez, Christian Harder, Uwe Pilz, and Chris Wyatt found Faye to be a moderately condensed object with a coma diameter between 1.2’ and 5’. Pilz and Wyatt reported a tail up to 5’ in length. The tail is a major feature in images taken of Faye. Images continue to show an asymmetric coma with a persistent anti-sunward jet-like feature.
Faye is a morning object observable from both hemispheres as its moves through Orion (Oct 1-13), Gemini (13-30), and Monoceros (30-31).
Photo Op: Faye passes in front of the large emission nebula Sh2-261 on October 3-5. Sh2-261 is located in the club of Orion. [Editor’s Note: I mistakenly called this nebula to the Rosette Nebula in last month’s Comet News. Embarrassing!].
6P/d’Arrest
Discovered on 1851 June 28 by the Heinrich Ludwig d'Arrest
Orbit (from Syuichi Nakano, Nakano Note NK 4445)
6P/d'Arrest
Epoch 2021 Sept. 23.0 TT = JDT 2459480.5
T 2021 Sept. 17.78204 TT Nakano
q 1.3546116 (2000.0) P Q
n 0.15061475 Peri. 178.10208 +0.73305041 +0.64381249
a 3.4985739 Node 138.93551 -0.62836543 +0.76449697
e 0.6128103 Incl. 19.51238 -0.26037278 -0.03240149
P 6.54
From 1865 observations 2008-2021, mean residual 0".66.
Nongravitational parameters A1 = +0.35 +/- 0.01, A2 = +0.1180 +/- 0.0005.
The comet has made 21 appearances since AD 1678 (IAUC 5283).
Comet will pass 0.97 AU from Jupiter on 2039 Apr. 1 UT.
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-Oct-01 18 43 -27 25 1.363 0.892 91E Sgr 10.4 21 68
2021-Oct-06 19 02 -28 51 1.371 0.920 91E Sgr 10.3 20 68
2021-Oct-11 19 21 -30 00 1.381 0.951 90E Sgr 10.3 19 67
2021-Oct-16 19 41 -30 52 1.393 0.985 89E Sgr 10.2 19 66
2021-Oct-21 20 01 -31 26 1.408 1.022 88E Sgr 10.2 18 65
2021-Oct-26 20 20 -31 44 1.424 1.061 87E Sgr 10.2 18 64
2021-Oct-31 20 40 -31 47 1.443 1.103 86E Mic 10.2 18 62
2021-Nov-05 20 59 -31 35 1.463 1.148 85E Mic 10.2 18 60
Comet Magnitude Formula (from fit to ALPO and COBS data, seasonal offset fixed at T+60 days)
m1 = 6.6 + 5 log d + 24.8 log r(t-60)
Heinrich Louis d’Arrest discovered 6P visually in June 1851. We now know that it had also been observed by Phillipe la Hire in 1678. Long-time comet watchers may remember this comet’s excellent apparition in 1976 when it passed 0.15 au from Earth and reached 5th magnitude. d’Arrest’s perihelion distance is larger now (1.35 au) so such close approaches are no longer possible. This year, closest approach to Earth was on August 2 at 0.75 au and perihelion on September 17.
d’Arrest usually possesses an asymmetrical lightcurve with respect to perihelion. In d’Arrest’s case, it means the comet is at its brightest nearly a month after perihelion. If this is true this return, it should peak in brightness this month at around magnitude 10.2. Last month we received magnitude estimates from Chris Wyatt, original mag 13.6, aperture corrected mag 13.0, on September 8 and J. J. Gonzalez, original mag 11.1, aperture corrected mag on 10.8, on September 8. COBS CCD observations by Michael Lehmann are more in line with the brightness reported by Gonzalez. The difference in brightness may be a function of the observed coma diameter. Gonzalez and Lehmann reported coma diameters on the order of 5’ while Wyatt saw a much smaller coma (0.8’).
d’Arrest should peak in brightness later this month at around magnitude 10.2 as it moves through the evening constellations of Sagittarius (Oct 1-27) and Microscopium (27-31).
Photo Op Alert: 6P passes within 10’ of bright globular cluster M55 on October 15 and within 10’ of 11th mag galaxy NGC 6925 on the 29th.
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-S45)
19P/Borrelly
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5
T 2022 Feb. 2.01452 TT Rudenko
q 1.3064503 (2000.0) P Q
n 0.14398101 Peri. 351.91587 +0.38679938 -0.79274184
a 3.6052266 Node 74.24796 +0.87108982 +0.14643746
e 0.6376232 Incl. 29.30738 +0.30263636 +0.59170638
P 6.85
From 1655 observations 2000 May 2-2017 Mar. 30, mean residual 1".3.
Nongravitational parameters A1 = +0.20, A2 = -0.0380.
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-Oct-01 23 29 -58 49 1.910 1.235 116E Tuc 13.0 0 71
2021-Oct-06 23 21 -58 23 1.873 1.225 114E Tuc 12.8 0 72
2021-Oct-11 23 15 -57 41 1.837 1.216 111E Tuc 12.5 0 72
2021-Oct-16 23 10 -56 43 1.801 1.209 109E Tuc 12.3 0 73
2021-Oct-21 23 07 -55 31 1.765 1.203 106E Gru 12.1 0 75
2021-Oct-26 23 04 -54 04 1.730 1.198 103E Gru 11.8 0 76
2021-Oct-31 23 04 -52 25 1.696 1.194 101E Gru 11.6 0 78
2021-Nov-05 23 04 -50 34 1.662 1.190 98E Gru 11.4 0 79
Comet Magnitude Formula (from Seiichi Yoshida)
m1 = 5.5 + 5 log d + 25.0 log r
2021 has seen a few low numbered short-period comets come within range of typical backyard telescopes. Tough perihelion isn’t till next February 2nd, 19P/Borrelly should become brighter than 10th magnitude this December on its way to a peak around magnitude 9.0.
Alphonse Borrelly discovered 10 comets and 18 Main Belt asteroids from the Marseille Observatory. In addition to his discovery of periodic comet 19P/Borrelly in 1904, Borrelly also discovered C/1873 Q1 (Borrelly), C/1874 O1 (Borrelly), C/1874 X1 (Borrelly), C/1877 C1 (Borrelly), C/1889 X1 (Borrelly), C/1900 O1 (Borrelly-Brooks), C/1903 M1 (Borrelly), C/1909 L1 (Borrelly-Daniel), C/1912 V1 (Borrelly).
The current apparition marks the comet’s 16th observed return. 19P’s orbit has been stable since discovery with perihelion staying between 1.30 and 1.46 au (this year it is at 1.31 au so nearly as close as it’s been since discovery). The comet approached within 1 au of Earth during its first 4 observed returns (1904, 1911, 1918 and 1925) and peaked between 8th and 10th magnitude. There was a stretch of 6 perihelion passages between 1938 and 1974 when the comet arrived at perihelion almost directly behind the Sun at ~2.3 to 2.5 au from Earth. Returns in 1987 and 1994 were much better with approaches to 0.48 and 0.62 au of Earth and peaks at magnitude 7 and 7.5, respectively. 2022 starts a new cycle of good apparitions. Though still a distant 1.18 au from Earth at its closest this time around, it will come closer in 2028 (0.41 au) and 2035 (0.62 au). The 2028 will be Borrelly’s best observed return.
October sees 19P limited to observers in the southern hemisphere as it moves through the southern constellations of Tucana (Oct 1-17) and Grus (17-31). It should begin the month around magnitude 13.0 and end the month close to 11.5. A peak brightness of magnitude 9 or so should be reached in January and February.
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-S45)
29P/Schwassmann-Wachmann
Epoch 2021 July 5.0 TT = JDT 2459400.5
T 2019 Mar. 26.66253 TT Rudenko
q 5.7691447 (2000.0) P Q
n 0.06642072 Peri. 49.15125 +0.99219414 -0.03308628
a 6.0385641 Node 312.37551 -0.03076331 +0.86941959
e 0.0446165 Incl. 9.36679 +0.12084872 +0.49296539
P 14.8
From 9998 observations 2018 June 18-2021 Aug. 11, 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-Oct-01 04 57 +31 53 5.918 5.488 110M Aur 82 18
2021-Oct-06 04 57 +31 59 5.919 5.417 115M Aur 82 18
2021-Oct-11 04 57 +32 04 5.921 5.350 120M Aur 82 18
2021-Oct-16 04 56 +32 08 5.922 5.286 125M Aur 82 18
2021-Oct-21 04 55 +32 11 5.923 5.227 130M Aur 82 18
2021-Oct-26 04 54 +32 14 5.925 5.172 135M Aur 82 18
2021-Oct-31 04 52 +32 15 5.926 5.123 140M Aur 82 18
2021-Nov-05 04 50 +32 16 5.928 5.079 146M Aur 82 18
29P/Schwassmann-Wachmann was discovered photographically on 1927 November 15 by German observing team Arnold Schwassmann and Arno Arthur Wachmann. The duo discovered 4 comets together, three short-period comets (29P/Schwassmann-Wachmann, 31P/Schwassmann-Wachmann, and 73P/Schwassmann-Wachmann) and a long-period comet shared with Leslie Peltier [C/1930 D1 (Peltier-Schwassmann-Wachmann)].
29P is one of the more enigmatic comets. It is always active and rarely fainter than 17th-18th magnitude. Multiple times per year outbursts occur resulting in a peak brightness that can reach 10th magnitude though most peaks fall in the 11th to 14th magnitude range. Richard Miles (Director of the British Astronomical Society’s Asteroids and Remote Planets Section) has published a series of papers on 29P and its outbursts. He found that as many as 6 active areas are producing outbursts on a nucleus with a rotation period of ~57-58 days.
29P is also considered a member of the Centaur population. Different organizations have different definitions for what constitutes a member of the Centaurs. The two most common definitions are from the Minor Planet Center (perihelion beyond the orbit of Jupiter and semi-major axis within the orbit of Neptune) and the Jet Propulsion Laboratory (semi-major axis between the orbits of Jupiter and Neptune). Both definitions would classify 29P as a Centaur.
29P has experienced a rare quadruple outburst on the nights of September 25 and 27. As a result, visual observations reported to the COBS site are reporting the comet to be as bright as magnitude 10.7. The comet is a morning object in Auriga and observable from both hemispheres. If you observe 29P, please consider contributing to two pro-am efforts to better understand this object: the British Astronomical Society’s (BAA) Mission 29P monitoring program coordinated by Richard Miles. ( https://britastro.org/node/18562 & https://britastro.org/node/25120 ) and the University of Maryland’s 29P Observation campaign (https://wirtanen.ast...P/29P_obs.shtml).
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 Syuichi Nakano, Nakano Note NK 4448)
C/2017 K2 (PANSTARRS)
Epoch 2022 Dec. 7.0 TT = JDT 2459920.5
T 2022 Dec. 19.67178 TT Nakano
q 1.7969443 (2000.0) P Q
z -0.0004734 Peri. 236.19715 +0.01818315 +0.04923207
+/-0.0000004 Node 88.23537 -0.18094861 +0.98245608
e 1.0008506 Incl. 87.56309 -0.98332445 -0.17987844
From 4213 observations 2013 May 12-2021 May 3, mean residual 0".44.
(1/a)org.= +0.000028, (1/a)fut.= +0.001121 (+/-0.000000), Q= 9.
The comet will pass 2.66 AU from Jupiter on 2024 Oct. 15 and
7.88 AU from Uranus on 2029 Oct. 16 UT.
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-Oct-01 16 59 +26 25 5.204 5.430 71E Her 12.0 53 10
2021-Oct-06 17 01 +25 26 5.160 5.437 68E Her 12.0 50 7
2021-Oct-11 17 02 +24 27 5.117 5.443 65E Her 12.0 48 5
2021-Oct-16 17 05 +23 30 5.074 5.448 63E Her 11.9 45 1
2021-Oct-21 17 07 +22 35 5.030 5.450 60E Her 11.9 43 0
2021-Oct-26 17 09 +21 42 4.987 5.451 57E Her 11.9 40 0
2021-Oct-31 17 12 +20 50 4.943 5.449 54E Her 11.8 37 0
2021-Nov-05 17 15 +20 01 4.899 5.444 52E Her 11.8 35 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. For comparison Uranus has a semi-major axis of 19.2 au.
C/2017 K2 (PANSTARRS) is over a year from its 2022 December 19 perihelion at 1.80 au when it should reach 6-7th magnitude. Several visual observations were made in September by J. J. Gonzalez, Christian Harder and Chris Wyatt as well as a CCD measurement by Carl Hergenrother. The visual measurements ranged between 11.6 and 12.9 (corrected magnitudes between 11.2 and 12.8). All observers found a small slightly condensed coma of ~1.2-2.2’.
C/2017 K2 is an evening object in Hercules and is better placed for northern observers though it also visible from the southern hemisphere. The comet will continue to slowly brighten throughout the remainder of 2021 and all of 2022.
C/2021 A1 (Leonard)
Discovered 2021 January 3 by Greg Leonard of the Catalina Sky Survey with the 1.5-m on Mount Lemmon
Dynamically old long-period comet
Orbit (from Syuichi Nakano, private email)
C/2021 A1 (Leonard)
Epoch 2022 Jan. 21.0 TT = JDT 2459600.5
T 2022 Jan. 3.30335 TT Nakano
q 0.6152670 (2000.0) P Q
z -0.0000212 Peri. 225.09253 +0.63774456 +0.29160589
+/-0.0000016 Node 255.89525 +0.72790936 -0.53080844
e 1.0000131 Incl. 132.68634 -0.25185283 -0.79574393
From 1054 observations 2020 Apr. 11-2021 Sept. 29, mean residual 0".54.
(1/a)org.= +0.000524, (1/a)fut.= -0.000081 (+/-0.000002), Q= 8.
The comet will pass 0.23 AU from the Earth on 2021 Dec. 12.5 UT.
Also comet will pass 0.029 AU from Venus on 2021 Dec. 18.0 UT.
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)
C/2021 A1 (Leonard) Max El
(deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Oct-01 11 18 +37 43 1.858 2.445 43M UMa 12.8 21 0
2021-Oct-06 11 23 +37 12 1.784 2.319 46M UMa 12.5 24 0
2021-Oct-11 11 27 +36 42 1.710 2.187 49M UMa 12.3 27 0
2021-Oct-16 11 32 +36 14 1.635 2.049 51M UMa 12.0 31 0
2021-Oct-21 11 38 +35 47 1.560 1.904 54M UMa 11.6 34 0
2021-Oct-26 11 43 +35 22 1.484 1.753 57M UMa 11.3 37 0
2021-Oct-31 11 49 +34 57 1.407 1.597 60M UMa 10.9 40 0
2021-Nov-05 11 56 +34 34 1.330 1.435 63M UMa 10.5 43 0
Comet Magnitude Formula (from ALPO and COBS data)
m1 = 7.4 + 5 log d + 11.7 log r [through T-325 days, where T = date of perihelion]
m1 = 11.4 + 5 log d + 5.7 log r [T-325 to T-178 days]
m1 = 5.2 + 5 log d + 18.8 log r [T-178 to T-112 days]
m1 = 8.7 + 5 log d + 8.0 log r [from T-112 days onward]
While no comet as spectacular as C/2020 F3 (NEOWISE) is predicted to happen anytime soon, there is hope that C/2021 A1 (Leonard) will at least be a nice binocular or even faint naked eye comet this December. Catalina Sky Survey astronomer Greg Leonard found C/2021 A1 on 2021 January 3 with the Mount Lemmon 1.5-m reflector when the comet was around magnitude 19 and 5.1 au from the Sun at discovery. Pre-discovery observations from Mount Lemmon and PANSTARRS were found back to April 2020 (when the comet was 7.5 au from the Sun).
An analysis of magnitude estimates submitted to the Minor Planet Center (MPC) in 2020, Comet Observation Database (COBS) and the ALPO in 2021 finds an object that has changed its rate of brightening at least twice already. The 2020 MPC data showed a healthy brightening of 2.5n = 11.7. That rate slowed to dramatically to 2.5n = 5.7 for most of 2021 up till July. A 2.5n = 5 rate means steady state so for the first half of 2021, C/2021 A1 was experiencing little, if any, increase in dust production. Since July, the comet has kicked back into high gear brightening at a 2.5n = 18.8 rate.
So far, all magnitude measurements have been from CCD/CMOS cameras with no visual observations submitted to the COBS site or the ALPO. Hopefully with the comet becoming better placed in the morning sky and brighter, visual observers will be able to measure its brightness. Unfortunately, the comet is located far to the north in Ursa Major and only visible from the northern hemisphere. Southern observers will have to wait till mid-December to catch a glimpse of Leonard.
Assuming a conservative 2.5n ~ 8 brightening rate from here on out would see Leonard around magnitude 13 at the start of October and magnitude 11 at the end of the month. The comet could be even brighter if its recent rapid brightening trend continues. A conservative 2.5n value of 8 would result in a peak brightness around magnitude 4.5 when the comet approaches within 0.233 au from Earth on December 12. With a large phase angle reaching 160 degrees at that time, forward scattering of light by cometary dust may increase Leonard’s brightness by an additional 1-3 magnitudes. Working against it are very difficult observing circumstance due to a small solar elongation at the time of maximum brightness (minimum elongation of 15 deg) resulting in the possibility that the comet may be too faint to be seen while so close to the Sun. We should have a much better idea of how bright Leonard is getting by the end of October.
Fainter Comets of Interest (Fainter than 13.0)
C/2021 O3 (PANSTARRS)
Discovered 2021 July 26 by Pan-STARRS with the 1.8-m Pan-STARRS1 1.8-m on Haleakala
Orbit (from Syuichi Nakano, private email)
C/2021 O3 (PANSTARRS)
T 2022 Apr. 21.06633 TT Nakano
q 0.2875278 (2000.0) P Q
Peri. 299.96269 -0.56813846 -0.81232240
Node 189.06692 +0.64671103 -0.53970622
e 1.0 Incl. 56.70663 -0.50890425 +0.22101925
From 277 observations 2021 July 26-Sept. 24.
Ephemerides (produced with Seiichi Yoshida’s Comets for Windows program)
C/2021 O3 (PANSTARRS) Max El
(deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Oct-01 22 25 +22 33 3.527 2.665 144E Peg 17.6 73 27
2021-Oct-06 22 19 +21 25 3.465 2.631 140E Peg 17.5 71 29
2021-Oct-11 22 14 +20 13 3.402 2.605 136E Peg 17.4 70 30
2021-Oct-16 22 10 +18 57 3.338 2.586 132E Peg 17.4 69 31
2021-Oct-21 22 06 +17 40 3.274 2.573 127E Peg 17.3 68 32
2021-Oct-26 22 02 +16 22 3.210 2.566 122E Peg 17.2 66 33
2021-Oct-31 22 00 +15 04 3.145 2.564 117E Peg 17.1 65 33
2021-Nov-05 21 57 +13 47 3.079 2.567 112E Peg 17.1 64 33
Comet Magnitude Formula (based on data submitted to the COBS and the MPC)
m1 = 11.1 + 5 log d + 8 log r
New Discoveries, Recoveries and Other Comets News
15P/Finlay – After reaching magnitude 10.0-10.5 in July, short-period comet 15P/Finlay is now fainter than magnitude 13 and fading fast. A mystery surrounding Finlay is its lack of an associated meteor shower even though its orbit that comes within 0.01 au of Earth. CBET 5046 reports the detection of a newly recognized meteor shower on 2021 September 28 and 29 by CAMS video cameras in New Zealand and Chile and the Southern Argentina Agile MEteor Radar Orbital System (SAAMER-OS). A total of 13 meteors were detected though the CAMS team reports that the outburst is ongoing. The observed meteors were released during Finlay’s 1995 return. Two additional outbursts are predicted to occur on 2021 October 7 with activity centered at 00:35m UT (from its 2008 perihelion) and 03h55m (from its 2014 perihelion) though peak times could be .
Astronomical Telegram #14947 contains predictions for the 2021 October 6/7 activity from a number of different sources. While ZHR rates of 100s to 1000s are predicted, the shower is expected to consist mainly of meteors fainter than naked eye visibility. Still visual observers are encouraged to try and observe any activity.
The newly found shower is officially called the Arid meteor shower due to its radiant’s location at R.A. = 262.7 deg and Dec. = -57.8 deg in the southern constellation of Ara. The far southern radiant should make this a very difficult shower to observe from the northern hemisphere.
P/2021 R6 (Groeller) – Hannes Groeller of the Catalina Sky Survey used the Mount Lemmon 1.5-m to discover a new short-period comet on 2021 September 12 at 20th magnitude. Pre-discovery observations by Pan-STARRS were found from 2021 August 31 and September 4. P/2021 R6 has a 15.72-year orbital period and will arrive at perihelion on Halloween (2021 October 31) at 2.55 au. The comet is not likely to get any brighter. This is the 3rd comet to be named after Groeller. The other two also being short-period comets [P/2019 B2 (Groeller) and P/2019 V2 (Groeller)]. [CBET 5045, MPEC 2021-S113]
P/2021 R5 (Rankin) – Catalina Sky Survey observer David Rankin found his 8th comet (to be named for him) on 2021 September 9. Like P/2021 R6, P/2021 R5 was also discovered with the Mount Lemmon 1.5-m. Pre-discovery observations by Pan-STARRS and Catalina were found back to 2021 June 26. The newest Rankin comet was 19th magnitude at discovery and close to its peak in brightness. Perihelion will be on 2022 January 9 at 3.33 au. [CBET 5035, MPEC 2021-R257]
P/2021 R4 (Wierzchos) – The third Catalina short-period discovery of September was made by Kacper W. Wierzchos. Like the other two Catalina finds, this one was also found with the Mount Lemmon 1.5-m. P/2021 R4 was 20th magnitude at discovery on 2021 September 6. Pre-discovery observations by Pan-STARRS were found from two nights prior to discovery. The comet has a 13.4-year period and a perihelion on 2021 October 13 at 2.33 au. This is Kacper’s second amed comet after C/2020 H3 (Wierzchos). [CBET 5034, MPEC 2021-R256]
P/2021 R3 (PANSTARRS) – The Pan-STARRS1 1.8-m was used to discover this 21st magnitude comet on 2021 September 5. Pan-STARRS pre-discovery observations were found back to 2021 July 9. Syuichi Nakano’s orbit published on CBET 5033 found a possible close approach to Jupiter of 0.36 au in September 2002. The current orbit has perihelion on 2021 May 27 at 2.53 au. It is likely that the comet has already peaked in brightness. [CBET 5033, CBET 2021-R255]
C/2021 R2 (PANSTARRS) – On 2021 September 5, C/2021 R2 was found in three 45-s w-band images taken with the Pan-STARRS1 1.8-m. The comet was 20th magnitude at discovery which is likely as bright as it will get. Perihelion occurs on 2022 January 4 at 7.31 au. [CBET 5031, CBET 2021-R151]
P/2021 R1 (PANSTARRS) – Four 45-s w-band images taken on 2021 September 4 with the Pan-STARRS1 1.8-m were used to discover this 20th magnitude short-period comet. Perihelion occurs on 2021 December 17 at 4.89 au. The comet is likely as bright as it will get. Perhaps it will be brighter at its next return in 2045. [Ref: MPEC 2021-R150, CBET 5030]
C/2021 Q6 (PANSTARRS) – A new 21st magnitude comet was identified in four 120-s z-band images taken with the Pan-STARRS1 1.8-m on 2021 August 22. Numerous pre-discovery observations back to January 2021 were also found. C/2021 Q6 is another large perihelion object (T = 2024 March 24, q = 8.71 au). It should reach a peak brightness near magnitude 20 in 2023-2024. [Ref: MPEC 2021-R167, CBET 5032]
P/2021 HS (PANSTARRS) – Back on 2021 April 16, Pan-STARRS found 2021 HS, an apparently asteroidal 20th magnitude object. H. Sato was the first to notice cometary activity on images taken July 4 with a 0.51-m f/6.8 astrograph resulting in a new cometary designation of P/2021 HS (PANSTARRS). Perihelion occurred on 2021 August 6 at 0.80 au when it was near its peak brightness of 18th magnitude. With an 8.6-year period, it will be back at perihelion in 2030. [CBET 5043, MPEC 2021-S44]
As always, the Comet Section is happy to receive all comet observations, whether textual descriptions, images, drawings, magnitude estimates, or spectra. Please send your observations via email to the Comets Section < comets @ alpo-astronomy .org >, Comets Section Coordinator Carl Hergenrother < carl.hergenrother @ alpo-astronomy .org > and/or Comets Section Acting Assistant Coordinator Michel Deconinck < michel.deconinck @ alpo-astronomy .org >.
Thank you to everyone who contributed to the ALPO Comets Section!
Stay safe and enjoy the sky!
- Carl Hergenrother
Edited by Carl H., 04 October 2021 - 03:22 AM.
