BAA Comet Section : Comets discovered in 2021

Updated 2021 August 3


  • 2014 UN271 (Bernardinelli-Bernstein)
  • 2021 A1 (Leonard)
  • 2021 A2 (NEOWISE)
  • 2021 A3 (414P/STEREO)
  • 2021 A4 (NEOWISE)
  • 2021 A5 (P/PanSTARRS)
  • 2021 A6 (PanSTARRS)
  • 2021 A7 (NEOWISE)
  • 2021 A8 (416P/Scotti)
  • 2021 A9 (PanSTARRS)
  • 2021 A10 (NEOWISE)
  • 2021 A11 (419P/PanSTARRS)
  • 2021 A12 (P/Lemmon)
  • 2021 B1 (417P/NEOWISE)
  • 2021 B2 (PanSTARRS)
  • 2021 B3 (NEOWISE)
  • 2021 C1 (Rankin)
  • 2021 C2 (P/PanSTARRS)
  • 2021 C3 (Catalina)
  • 2021 C4 (ATLAS)
  • 2021 C5 (PanSTARRS)
  • 2021 C6 (Lemmon)
  • 2021 CT3 [A/PanSTARRS]
  • 2021 D1 (SWAN)
  • 2021 D2 (ZTF)
  • 2021 E1 (420P/Hill)
  • A/2021 E2 (A/Lemmon)
  • 2021 E3 (ZTF)
  • A/2021 E4 (A/Lemmon)
  • 2021 F1 (A/PanSTARRS)
  • 2021 G1 (Leonard)
  • A/2021 G2 (ATLAS)
  • 2021 G3 (PanSTARRS)
  • 2021 J1 (Maury-Attard)
  • 2021 J2 (PanSTARRS)
  • 2021 J3 (P/ATLAS)
  • 2021 K1 (ATLAS)
  • 2021 K2 (MASTER)
  • 2021 K3 (Catalina)
  • 2021 L1 (P/Christensen)
  • 2021 L2 (P/Leonard)
  • 2021 L3 (Borisov)
  • 2021 L4 (P/PanSTARRS)
  • 2021 L5 (P/La Sagra)
  • 2021 LB18 [A/PanSTARRS]
  • 2021 N1 (P/ZTF)
  • 2021 N2 (P/Fuls)
  • 2021 N3 (PanSTARRS)
  • 2021 O1 (Nishimura)
  • 2021 O2 (P/Kowalski)
  • 2021 O3 (PanSTARRS)

  • When observing a comet please try to forget how bright you think the comet should be, what it was when you last viewed it, what other observers think it is or what the ephemeris says it should be.

    The equations for the light curves of comets that are currently visible use only the raw observations and should give a reasonable prediction for the current brightness. If the comet has not yet been observed or has gone from view a correction for aperture is included, so that telescopic observers should expect the comet to be fainter than given by the equation. The correction is about 0.033 per centimetre. Values for the r parameter given in square brackets [ ] are assumed. The form of the light curve is either the standard m = H0 + 5 log d + K0 log r or the linear brightening m = H0 + 5 log d + L0 abs(t - T + D0) where T is the date of perihelion, t the present and D0 an offset, if L0 is +ve the comet brightens towards perihelion and if D0 is +ve the comet is brightest prior to perihelion.

    Observations of comets in 2021 are given in ICQ format. 

    Full details of recently discovered objects will not appear until they are available on the CBAT web pages. The actual accuracy of preliminary orbits is often (nearly always) much worse than the published accuracy implies.  In part this is because each orbital solution is treated as a mathematical construct and does not take account of observational error.  JPL does publish the errors, whereas the MPECs do not.


    2014 UN271 (Bernardinelli-Bernstein)
    Pedro Bernardinelli and Gary Bernstein of the Dark Energy Survey team using the Cerro Tololo 4.0 m reflector discovered a 22nd magnitude asteroid in images taken between 2014 October 20.29 and 2018 November 8.24. Sam Deen was able to find pre-discovery images taken with the CFHT at Mauna Kea on 2014 August 28. It is in a near parabolic, high inclination orbit with perihelion at 10.9 au in 2031 January. [MPEC 2021-M53, CBET 4983 2021 June 19/21]. Luca Buzzi reported that cometary activity was detected on June 22 in images taken with the 0.51 m SkyGems Remote Telescope in Namibia. It was then quickly re-designated as a comet. [MPEC 2021-M83, CBET 4989, 2021 June 24] It is a comet from the inner edge of the Oort cloud and has an absolute magnitude of 2.5, which may translate into a diameter of over 100 km.
    2021 A1 (Leonard)
    Gregory Leonard discovered a comet of 19th magnitude in images taken with the 1.5m reflector of the Mt Lemmon Survey on 2021 January 3.54. It was placed on the PCCP as C4AGJ62. There were prediscovery observations from Catalina Sky Survey (2020 December, 2021 January), Mt Lemmon Survey (2020 April, November), PanSTARRS (2020 April, May, June, August) and the Szeged Asteroid Program, Hungary (2020 November). [CBET 4907, MPEC 2021-A99, 2021 January 10]. The comet is at perihelion at 0.6 au in 2022 January. The comet will pass 0.23 au from the earth on 2021 December 12 and 0.0286 au from Venus on 2021 December 18.  The comet could come within visual range in 2021 October and reach 4th magnitude in December during its approach to Earth.  It then goes into solar conjunction and becomes poorly placed for northern observers.  Southern hemisphere observers will see it fading from 5th magnitude after conjunction later in December.
    2021 A2 (NEOWISE)
    An approximately 15th magnitude comet was discovered from the NEOWISE satellite on 2021 January 3.02. It was posted on the PCCP as N00ht7m. Ground-based observers confirmed the cometary nature, with Michael Mattiazzo reporting it as bright as 12th magnitude in his 0.2 m reflector. [CBET 4908, MPEC 2021-A100, 2021 January 10] It is at perihelion at 1.4 au in 2021 January. A southern circumpolar object at discovery, it is rapidly moving north and could brighten by a further magnitude.  For some reason the MPC leave it un-named in MPEC 2021-B143 [2021 January 31]
    2021 A3 (414P/STEREO)
    An object was discovered by the Zwicky Transient Factory on January 5.1 and posted on the PCCP as ZTF01on. It was summarily removed on January 8 and noted to be P/2016 J3. The previous evening Maik Meyer had discovered the identity, computed a linked orbit and informed the MPC and CBAT.  Maik's linked orbit shows that the period is 4.67 years, with perihelion at 0.53 au on January 25.  Despite this it has not been designated 2021 A1.  Michael Jaeger has imaged it, finding it to be around 14th magnitude.

    Sam Dean notes:

    It's caught in a Kozai resonance with Jupiter that it's currently on the higher-e, lower-i leg of. I think that'll peak around 2400-2500 before cycling back. Like plenty of Earth-crossing Kozai oscillating objects, its orbit also crosses Earth sometimes, creating a potential for meteor showers. It last crossed Earth's orbit within 0.1 au in the 1300s, coming as close as 0.07 au - and it will next do so in the 2200s/2300s, coming less than 0.01 au around 2300, where it should create a fairly regular and impressive meteor shower considering that it would be even more active than it is now.
    Sam also suggests that the absolute magnitude is very faint, around 23 and that it brightens rapidly, perhaps at 20 log r.

    Rather belatedly the CBAT issued CBET 4911 on January 11, with a revision coming 15 minutes later.  This gives a similar account to that given above and notes that the comet will pass Jupiter at 0.9 au in 2031 December.  It also hints that either the comet shows strong non-gravitational forces or that the 2016 positions are somewhat out. The MPC finally issued MPEC 2021-A157 on January 12. This does not give elements for 2016, although the published elements do use observations from 2016, so it may just be an oversight.  Perhaps because of the delays it also briefly appeared on the PCCP as P11c5Dk.
    2021 A4 (NEOWISE)
    An approximately 20th magnitude comet was discovered from the NEOWISE satellite on 2021 January 3.92. It was posted on the PCCP as N00htdm. The MPEC suggests that it was reported by NEOWISE as being cometary, however the CBET suggests that it was reported because of interesting motion and that ground-based observers confirmed the cometary nature. There were prediscovery observations from PanSTARRS on January 3.6. [CBET 4914, MPEC 2021-A207, 2021 January 15] It is at perihelion at 1.1 au in 2021 March. It appears to be an intrinsically faint object and if so won't come within visual range. Discovery magnitudes of NEOWISE objects are often fainter than seen by visual observers.  Alan Hale reported the comet as being 12.6 on February 6.16.
    2021 A5 (P/PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on January 6.30. It was placed on the PCCP as P11bxkC. There were prediscovery Mt Lemmon observations from 2020 December 16. [CBET 4915, MPEC 2021-A209, 2021 January 15] The comet was at perihelion at 2.6 au in 2020 November and has a period of 5.3 years.
    2021 A6 (PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on January 8.60. It was placed on the PCCP as P11bKhA. There were prediscovery Mt Lemmon observations from 2020 November 26 and December 22. [CBET 4916, MPEC 2021-A210, 2021 January 15] The comet was at perihelion at 7.9 au in 2021 April.
    2021 A7 (NEOWISE)
    An approximately 20th magnitude comet was discovered from the NEOWISE satellite on 2021 January 9.11. It was posted on the PCCP as N00hue0. [CBET 4917, MPEC 2021-A211, 2021 January 15/16] It is at perihelion at 2.0 au in 2021 July.  The CBET suggests that there is a possibility that it may be an intermediate period comet. It was posted as new object A10wPXq on April 29 and again as A10wXnm on May 2, probably as a result of the MPC supplying out of date elements.
    2021 A8 (416P/Scotti)
    Erwin Schwab recovered comet 2013 A2 as a nearly stellar object in images taken with the 0.8-m f/3 Schmidt reflector at Calar Alto, Spain, on January 14.01. [CBET 4919, MPEC 2021-B21, 2021 January 17]
    2021 A9 (PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on January 12.64. It was placed on the PCCP as P11bX5O. There were prediscovery Mt Lemmon observations from 2020 December 12 and 2021 January 9, and PanSTARRS 2 observations from 2020 December 24.  It may be an intermediate period comet.  [CBET 4922, MPEC 2021-B119, 2021 January 23] The comet is at perihelion at 7.7 au in 2023 November.
    2021 A10 (NEOWISE)
    An approximately 19th magnitude potential NEO was discovered from the NEOWISE satellite on 2021 January 12.16. It was posted on the PCCP as N00hurv. Subsequently astrometrists, including Peter Birtwhistle noted cometary features; Nick James also reported astrometry. [CBET 4930, MPEC 2021-C25, 2021 February 6] It is at perihelion at 1.3 au in 2021 March and has a long period, retrograde orbit. 
    2021 A11 (419P/PanSTARRS)
    Erwin Schwab recovered comet 2015 F1 as an apparently stellar object in images taken with the 0.8-m f/3 Schmidt reflector at Calar Alto, Spain, on January 13.06. Additional observations were made on February 10, 13 and 14. The comet was some 4' from the predicted position, implying a delta T of -0.2 days. The comet passed 0.46 au from Jupiter in 1975 December in an encounter that substantially reduced the perihelion distance. The comet is significantly fainter at this return than it was at the discovery return. [CBET 4933, MPEC 2021-D104, 2021 February 16/25].  It is not clear why there was such a long gap between the issue of the CBET and MPEC.
    2021 A12 (P/Lemmon)
    2008 CL94 was recovered in astrometry taken with the Gemini North 8.1 m telescope at Mauna Kea on January 9.27 and January 15. The comet passed 0.7 au from Jupiter in 1921 and 0.9 au from the planet in 1986. [MPEC 2021-M89 CBET 4992, 2021 June 26]. The MPEC does not say why there was such a long gap between the observations and announcement.
    2021 B1 (417P/NEOWISE)
    Erwin Schwab recovered comet 2015 J3 as a nearly stellar object in images taken with the 0.8-m f/3 Schmidt reflector at Calar Alto, Spain, on January 17.23. The comet passed 0.48 au from Jupiter in 1952 August and will pass 0.43 au from the planet in 2024 September in an encounter that will increase the perihelion distance from 1.49 to 1.57 au. [CBET 4920, MPEC 2021-B118, 2021 January 22/23]
    2021 B2 (PanSTARRS)
    PanSTARRS 1 discovered a 20th magnitude comet in images taken with the 1.8m Ritchey-Chretien on January 17.23. It was placed on the PCCP as P11cite. There were prediscovery Catalina Sky Survey observations from 2020 December 12 and PanSTARRS 1 observations from 2020 December 24. [CBET 4921, MPEC 2021-B120, 2021 January 23] The comet is at perihelion at 2.5 au in 2021 May.
    2021 B3 (NEOWISE)
    An approximately 19th magnitude comet was discovered from the NEOWISE satellite on 2021 January 22.25. It was posted on the PCCP as N00hwa7. [CBET 4929, MPEC 2021-C16, 2021 February 4] It is at perihelion at 2.2 au in 2021 March and has a period of around 150 years
    2021 C1 (Rankin)
    David Rankin discovered a comet of 20th magnitude in images taken with the 1.5m reflector on February 11.44 during the Mt Lemmon Survey. It was placed on the PCCP as C4WH682. [CBET 4934, MPEC 2021-D102, 2021 February 24/25]. The comet was at perihelion at 3.5 au in 2020 December.
    2021 C2 (P/PanSTARRS)
    PanSTARRS 1 discovered a 22nd magnitude comet in images taken with the 1.8m Ritchey-Chretien on February 12.53. It was placed on the PCCP as P11dgUs. There were prediscovery Mt Lemmon observations from 2021 January 17. [CBET 4935, MPEC 2021-D103, 2021 February 24/25] The comet was near perihelion at 4.9 au and has a period of around 30 years.
    2021 C3 (Catalina)
    An object of 19th magnitude was discovered in Catalina Sky Survey images taken with the 0.68m Schmidt on February 7.46. PanSTARRS 1 reported cometary features and it was placed on the PCCP as C1VUXJ1. There were pre-discovery Catalina images from January 16. [MPEC 2021-D112, CBET 4936, 2021 February 26]. The comet was near perihelion at 2.3 au and has a period of around 500 years in a retrograde orbit.
    2021 C4 (ATLAS)
    A 19th magnitude object was discovered in images taken with the 0.5m Schmidt at Haleakala on February 12.61 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) team. It was posted on the PCCP as A10vcA4 following reports of signs of cometary activity. [CBET 4937, MPEC 2021-D113, 2021 February 26]. The comet was at perihelion at 4.5 au in 2021 January.
    2021 C5 (PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on February 12.35. It was placed on the PCCP as P11dcTx. There were prediscovery PanSTARRS observations from 2020 December 22 2021 January 23 and February 6 and Mt Lemmon observations from 2021 January 18. [CBET 4941, MPEC 2021-E64, 2021 March 8] The comet is at perihelion at 3.2 au in 2023 February.
    2021 C6 (Lemmon)
    The Mt Lemmon Survey discovered a potential NEO of 21st magnitude in images taken with the 1.5m reflector on February 7.43. It was placed on the PCCP as C4V28F2. Confirmation astrometry showed cometary features and pre-discovery images from PanSTARRS were found from January 23. [CBET 4946, MPEC 2021-F63, 2021 March 21]. The comet is at perihelion at 3.3 au in 2021 November. It is in a hyperbolic retrograde orbit.
    2021 CT3 [A/PanSTARRS]
    PanSTARRS 1 discovered an asteroid in images taken with the 1.8m Ritchey-Chretien on 2021 February 7.37. The object, classified by JPL as a Centaur, is at perihelion at 4.3 au in 2021 December and is in a retrograde orbit with a period of around 20 years. It briefly appeared on the PCCP as P11czUb.
    2021 D1 (SWAN)
    Michael Mattiazzo discovered a comet on February 25 in SWAN images taken since February 19 and this was confirmed in ground based images taken by Michael Jaeger on February 28.  The comet is currently poorly placed for visual observation, but is imageable.  The comet was near perihelion at 0.9 au and will fade.  Nick James, Denis Buczynski, Werner Hasubick and Richard Miles all made confirmatory images and astrometery of the comet. The MPC published an orbit and designated the comet in MPEC 2021-E19 [2021 March 4]. This gave an orbit with a period of around 75 years. CBET 4939 appeared five hours later on March 5 and gave a parabolic orbit based on a shorter arc with fewer observations, though with much more detail about the confirming observations.
    2021 D2 (ZTF)
    The Zwicky Transient Facility reported observations of a 19th magnitude possible NEO made on February 19.55 with the 1.2m Oschin Schmidt. This was placed on the PCCP as ZTF0KcP and subsequently found to show cometary features by astrometrists.  The CBET note that it is the same object as ZTF0Kii reported on March 13.7  [CBET 4947, 4948 (a correction), MPEC 2021-F67, 2021 March 22]. The comet is at perihelion at 2.9 au in 2022 February.
    2021 E1 (420P/Hill)
    Erwin Schwab recovered comet 2009 Q1 as a stellar object in images taken with the 0.8-m f/3 Schmidt reflector at Calar Alto, Spain, on March 11.13. The recovery was confirmed by Diana Abreu using the 1.0m reflector at the ESA Optical Ground Station, Tenerife on March 14. The comet was some 9' from the expected position and does not reach perihelion until 2022 May. When Syuichi Nakano computed a linked orbit the observations showed that non-gravitiational parameters were required. When these were included it was found that the 1996 observations reported by Rob Matson were of the comet, though his 1998 measurements did not fit so well. [CBET 4943, MPEC 2021-F07, 2021 March 16/17]
    2021 E2 (A/Lemmon)
    The Mt Lemmon Survey discovered an object of 21st magnitude in images taken with the 1.5m reflector on March 7.39. It was placed on the PCCP as C4ZL362. No evidence for cometary activity has been detected and the object has passed perihelion. [MPEC 2021-H143, 2021 April 28]. The object was at perihelion at 2.3 au in 2020 December. It is in a long-period retrograde orbit.
    2021 E3 (ZTF)
    The Zwicky Transient Facility reported observations of a 20th magnitude possible NEO made on March 9.53 with the 1.2m Oschin Schmidt. This was placed on the PCCP as ZTF0Kij and subsequently found to show cometary features by astrometrists.  [CBET 4960, MPEC 2021-J71, 2021 May 6/7]. The comet is at perihelion at 1.8 au in 2022 June.  It could reach 11th magnitude around the time of perihelion when it will be at high southern declination.
    2021 E4 (A/Lemmon)
    The Mt Lemmon Survey discovered an object of 21st magnitude in images taken with the 1.5m reflector on March 7.32. It was placed on the PCCP as C5DDQL2. There were pre-discovery images from PanSTARRS in 2020 December, 2021 January and February. No evidence for cometary activity has been detected but the object has not yet passed perihelion. [MPEC 2021-M78, 2021 June 23]. The object is at perihelion at 4.7 au in 2022 April. It is in a long-period retrograde orbit.
    2021 F1 (A/PanSTARRS)
    PanSTARRS 1 discovered an asteroid in images taken with the 1.8m Ritchey-Chretien on 2021 March 19.41. It was placed on the PCCP as P11e2jE. There were fractionally earlier observations from Mt Lemmon. [MPEC 2021-H142, 2021 April 27] The object is at perihelion at 1.0 au in 2022 April and is in a retrograde orbit. It may well show cometary activity as it approaches perihelion.  Unfortunately it is a poor return with the object being in conjunction on the opposite side of the Sun at perihelion.
    2021 G1 (Leonard)
    Gregory Leonard discovered a comet of 21st magnitude in images taken with the 1.5 m reflector of the Mt Lemmon Survey on 2021 April 11.33. It was placed on the PCCP as C5EEGT2. [CBET 4959, MPEC 2021-J72, 2021 May 6]. The comet is at perihelion at 3.4 au in 2021 July and is in a long period orbit.  It passed 0.5 au from Saturn in 2018 March.
    2021 G2 (A/ATLAS)
    A 19th magnitude object was discovered by the ATLAS (Asteroid Terrestrial-impact Last Alert System) team in images taken with the 0.5m Schmidt at Mauna Loa on April 11.25. It was posted on the PCCP as A10wotD. No cometary activity has been detected (by professional observers) to date. [MPEC 2021-M79, 2021 June 23]. The object is at perihelion at 5.0 au in 2024 September. CBET 4988 [2021 June 24] suggests that cometary activity has been detected and the object is probably a comet.
    2021 G3 (PanSTARRS)
    PanSTARRS 1 discovered a 22nd magnitude potential NEO in images taken with the 1.8m Ritchey-Chretien on April 1.26. With the PanSTARRS group finding signs of cometary activity it was placed on the PCCP as P11ebKr. There were prediscovery Mt Lemmon observations from 2021 February and Catalina Sky Survey observations using the Kitt Peak Bok telescope in March. [CBET 4990, MPEC 2021-M86, 2021 June 25] The comet is at perihelion at 5.2 au in 2021 October.
    2021 J1 (Maury-Attard)
    Alain Maury and Georges Attard discovered a comet of 19th magnitude in images taken with the 0.28 m Schmidt of the MAP Observatory, San Pedro de Atacama, Chile (W94) on 2021 May 9.33. It was placed on the PCCP as 1581K01. [CBET 4972, MPEC 2021-K11, 2021 June 2]. The comet was at perihelion at 1.7 au in 2021 February and has a period of around 130 years. The MAP observatory is named for the initial letters of the last names of the amateur astronomers Alain Maury, Georges Attard and Daniel Parrot who own and run the observatory, which is dedicated to finding new asteroids and comets.
    2021 J2 (PanSTARRS)
    PanSTARRS 1 discovered a 22nd magnitude comet in images taken with the 1.8m Ritchey-Chretien on May 10.41. It was placed on the PCCP as P11g7TN. There were prediscovery PanSTARRS observations from 2021 March, April and May and Mt Lemmon observations from earlier on May 10. [CBET 4973, MPEC 2021-L24, 2021 June 2] The comet is at perihelion at 4.7 au in 2021 September.
    2021 J3 (P/ATLAS)
    A 19th magnitude object was discovered in images taken with the 0.5m Schmidt at Haleakala on May 13.55 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) team. It was posted on the PCCP as A10xbi7 following reports of signs of cometary activity in follow up images (and subsequently given as 2021 A3 on the list of previous NEO confirmations). [CBET 49xx, MPEC 2021-L26, 2021 June 3]. The comet was at perihelion at 4.9 au in 2019 June and has a period of around 25 years.
    2021 K1 (ATLAS)
    A 17th magnitude object was discovered in images taken with the 0.5m Schmidt at Haleakala on May 24.61 by the ATLAS (Asteroid Terrestrial-impact Last Alert System) team. It was posted on the PCCP as A10xB7g with an earlier discovery date of May 14.59 as this had been submitted to the MPC as an isolated tracklet. There were many PanSTARRS pre-discovery observations back to 2020 April. [CBET 4968, MPEC 2021-K89, 2021 May 27]. The comet was at perihelion at 2.5 au in 2021 May and has a period of around 45 years.
    2021 K2 (MASTER)
    The MASTER team reported the discovery of a 19th magnitude comet found using the MASTER (Mobile Astronomical System of the Telescope-Robots) auto detection system with the robotic 0.4m f/2.5 reflector at the SAAO, Sutherland, South Africa on May 22.98, with prediscovery images from earlier in May. It was confirmed by other observers. [CBET 4975, MPEC 2021-L89, 2021 June 9]. The comet will reach perihelion at 5.5 au in 2021 August. 
    2021 K3 (Catalina)
    A potential NEO of 22nd magnitude was discovered in Catalina Sky Survey images taken with the 2.25 m Bok telescope at Kitt Peak on May 20.42. PanSTARRS 1 reported cometary features and it was placed on the PCCP as C076EZ5. [MPEC 2021-M87, CBET 4991, 2021 June 25]. The comet is at perihelion at 5.2 au in 2022 February.
    2021 L1 (P/Christensen)
    Cristovao Jacques recovered comet 2006 S4 at the SONEAR observatory on 2021 June 5.32. Taras Prystavski independently recovered the comet on 2021 June 15.75 using the 0.5 m iTelescope at Siding Spring, some 9' from the ephemeris position. The recovery was reported on the comets-ml on June 15/16, with Jacques noting that he had sent the observations to the MPC 10 days previously. The MPC is a bit behind with processing comet observations and did not announce the recovery until June 17 [MPEC 2021-M34, CBET 4979]
    2021 L2 (P/Leonard)
    Gregory Leonard discovered a comet of 20th magnitude in images taken with the 1.5m reflector of the Mt Lemmon Survey on 2021 June 8.40. It was placed on the PCCP as C5QPCV2. There were prediscovery observations from the Mt Lemmon Survey and PanSTARRS in 2021 May. [CBET 4984, MPEC 2021-M74, 2021 June 22]. The comet is at perihelion at 1.9 au in 2021 July and has a period of 8.2 years.
    2021 L3 (Borisov)
    Gennady Borisov discovered an 20th magnitude comet in images taken with the MARGO 0.65-m f/1.5 astrograph at Nauchnij, Crimea on June 8.91. It was placed on the PCCP as gb00279 and quickly confirmed by other astrometrists. [CBET 4885, MPEC 2021-M75, 2021 June 22] The comet is at perihelion at 8.4 au in 2022 March.
    2021 L4 (P/PanSTARRS)
    PanSTARRS 1 discovered a 21st magnitude comet in images taken with the 1.8m Ritchey-Chretien on June 14.27. It was placed on the PCCP as P11h3rz. There were prediscovery Spacewatch and PanSTARRS observations from earlier in the month. [CBET 4986, MPEC 2021-M77, 2021 June 23] The comet was at perihelion at 2.8 au in 2019 September and has a period of 5.6 years. Given the long time since perihelion it might be in outburst.
    2021 L5 (P/La Sagra)
    Images of 2012 S2 were found in incidental PanSTARRS 1 asrometry taken with the 1.8m Ritchey-Chretien on June 6.53. It was independently found later in images from ATLAS at Mauna Loa. [CBET 4994, MPEC 2021-N47, 2021 July 8] The comet is at perihelion at 1.4 au in 2021 October and has a period of 9.3 years.
    2021 LB18 [A/PanSTARRS]
    PanSTARRS 1 discovered an asteroid in images taken with the 1.8m Ritchey-Chretien on 2021 June 7.48. The object, classified by JPL as a Centaur, was at perihelion at 3.4 au in 2021 March and is in a retrograde orbit with a period of around 130 years. It appeared on the PCCP as P11gO7R. [MPEC 2021-M97, 2021 June 28]
    2021 N1 (P/ZTF)
    The Zwicky Transient Facility reported observations of a 19th magnitude comet made on July 2.46 with the 1.2m Oschin Schmidt. This was placed on the PCCP as ZTF0LHw. [CBET 4999, MPEC 2021-N115, 2021 July 13]. The comet was at perihelion at 1.0 au in 2021 June and has a period of around 5.1 years. 
    2021 N2 (P/Fuls)
    David Carson Fuls discovered an 18th magnitude comet in Catalina Sky Survey images taken with the 0.68-m Schmidt on July 9.44. It was placed on the PCCP as C266K41. There were pre-discovery Catalina images from June 27. [MPEC 2021-N137, CBET 5000, 2021 July 15/16]. The orbit is currently poorly constrained, but suggests that the comet is at perihelion at 3.8 au in late 2021 and may have a period of around 20 years, or be in a parabolic orbit. If periodic it may have passed 0.5 au from Saturn in 2015.
    2021 N3 (PanSTARRS)
    PanSTARRS 1 discovered a 22nd magnitude comet in images taken with the 1.8m Ritchey-Chretien on MJuly 13.52. It was placed on the PCCP as P11iNI. There were prediscovery PanSTARRS observations from 2021 June and July. [CBET 5003, MPEC 2021-O39, 2021 July 22/23] The comet was at perihelion at 5.7 au in 2020 August and may have a period of around 2000 years.
    2021 O1 (Nishimura)
    Japanese amateur Hideo Nishimura from Gansho-ji, Kakegawa discovered a comet with a digital camera (Canon EOS 6D + 200mm telephoto lens) on July 21.78. He originally thought that it might be an outburst of 8P/Tuttle.  Michael Jäger was amongst those confirming the object and he gives a total magnitude of 9.2. It was placed on the PCCP as HN002. [MPEC 2021-O47, CBET 5004, 2021 July 25]. The comet is at perihelion at 0.8 au in August. Unfortunately this timing is nearly as bad as it could be, putting the comet on the far side of the Sun and at poor elongation. The comet has been at less than 30 degrees elongation since February, which probably explains why it was not picked up previously by search programmes.
    2021 O2 (P/Kowalski)
    PanSTARRS 1 discovered a 20th magnitude comet in images taken with the 1.8m Ritchey-Chretien on July 20.60. It was identified as a return of 2005 W3 by the MPC. There were prediscovery PanSTARRS observations from 2020 September, October, November and December.  The comet was some 13' from the predicted position, corresponding to a delta T of around -1.0 days. [CBET 4506, MPEC 2021-O66, 2021 July 30] The comet is at perihelion at 2.9 au in 2021 September and has a period of 15.9 years. It made a distant encounter (1.1 au) with Saturn in 2014 July.
    2021 O3 (PanSTARRS)
    PanSTARRS 1 discovered a 20th magnitude comet in images taken with the 1.8m Ritchey-Chretien on July 26.48. It was placed on the PCCP as P11ibiE. [CBET 5009, MPEC 2021-P05, 2021 August 1/2] The comet is at perihelion at 0.3 au in 2022 April. The initial observations suggest a fairly faint absolute magnitude, so it may not survive perihelion. If it does it will become visible as a 6th magnitude object in the evening sky at the beginning of May and quickly become circumpolar. It will also quickly fade.
    Ephemerides of current comets are available on the CBAT ephemeris page and positions of newly discovered comets are on the Possible Comet Confirmation Page.
    More information on LINEAR. A list of comets discovered by selected search programs.
    The Northumberland refractor is the telescope that was used in the search for Neptune. It now has a 0.30-m f20 doublet lens which gives a stellar limiting magnitude of around 15 at the zenith on good nights. The Thorrowgood refractor was built in 1864 and has a 0.20-m f14 doublet lens; it is currently out of action as the dome has stuck.
    Published by Jonathan Shanklin. Jon Shanklin - jds@ast.cam.ac.uk