BAA Comet Section : Comets discovered in 2011

Updated 2013 December 20


  • 2011 A1 (250P/Larson)
  • 2011 A2 (P/Scotti)
  • 2011 A3 (Gibbs)
  • 2011 A4 (249P/LINEAR)
  • A/2011 AF3 [Catalina]
  • A/2011 BX59 [PanSTARRS]
  • 2011 C1 (McNaught)
  • 2011 C2 (P/Gibbs)
  • 2011 C3 (Gibbs)
  • 2011 CR42 (P/Catalina)
  • 2011 E1 (P/SOHO)
  • A/2011 ED78 [Mt Lemmon]
  • 2011 F1 (LINEAR)
  • 2011 FR143 (P/Lemmon)
  • 2011 G1 (McNaught)
  • A/2011 GO44 [Catalina]
  • 2011 H1 (Mt Lemmon) = 2002 VQ94 (LINEAR)
  • 2011 J1 (251P/LINEAR)
  • 2011 J2 (LINEAR)
  • 2011 J3 (LINEAR)
  • 2011 JB15 (P/Spacewatch-Boattini)
  • 2011 K1 (Schwartz-Holvorcem)
  • 2011 KP36 (Spacewatch)
  • 2011 L1 (McNaught)
  • 2011 L2 (McNaught)
  • 2011 L3 (McNaught)
  • 2011 L4 (PanSTARRS)
  • 2011 L5 (252P/LINEAR)
  • 2011 L6 (Boattini)
  • 2011 M1 (LINEAR)
  • A/2011 MT [Mt Lemmon]
  • A/2011 MC2 [Mt Lemmon]
  • 2011 N1 (P/ASH)
  • 2011 N2 (McNaught)
  • 2011 N3 (SOHO)
  • 2011 NO1 (P/Elenin)
  • 2011 O1 (LINEAR)
  • A/2011 OR17 [Siding Spring]
  • 2011 P1 (P/McNaught)
  • 2011 P2 (PanSTARRS)
  • 2011 Q1 (PanSTARRS)
  • 2011 Q2 (McNaught)
  • 2011 Q3 (P/McNaught)
  • 2011 Q4 (SWAN)
  • A/2011 QD23 [ISON-NM]
  • 2011 R1 (McNaught)
  • 2011 R2 (253P/PanSTARRS)
  • 2011 R3 (P/Novichonok-Gerke)
  • 2011 S1 (P/Gibbs)
  • 2011 S2 (Kowalski)
  • A/2011 SP25 [PanSTARRS]
  • 2011 U1 (P/PanSTARRS)
  • 2011 U2 (P/Bressi)
  • 2011 U3 (PanSTARRS)
  • 2011 UA134 (P/Spacewatch-PanSTARRS)
  • A/2011 UF256 [Mt Lemmon]
  • 2011 UF305 (LINEAR)
  • A/2011 UR402 [PanSTARRS]
  • 2011 V1 (P/Boattini)
  • 2011 VJ5 (P/Lemmon)
  • 2011 W1 (P/PanSTARRS)
  • 2011 W2 (P/Rinner)
  • 2011 W3 (Lovejoy)
  • A/2011 WS41 [PanSTARRS]
  • A/2011 XO3 [Catalina]
  • 2011 Y1 (255P/Levy)
  • 2011 Y2 (P/Boattini)
  • 2011 Y3 (Boattini)
  • A/2011 YU75 [Steward Observatory]

  • 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 new comets are given in ICQ format. More recent ones may be available in TA format from the main page.

    Full details of recently discovered objects will not appear until they are available on the CBAT web pages, which is usually a fortnight after the publication of the IAUC.


    Kracht Group SOHO comets
    2011 E1 (P/SOHO)(IAUC )
    was discovered with the SOHO LASCO coronographs and has not been observed elsewhere. It was a sungrazing comet of the Kracht group. IAUC 9201 [2011 March 21] gives an orbit by Gareth Williams linking 2011 E1 with 2000 O3 and 2005 W4. The orbital solution requires non gravitational parameters. There is a possibility that the comet might be visible to ground based telescopes during late March and early April, though it would certainly be fainter than 20th magnitude.

    For further information on the discovery of these objects see this year's SOHO discoveries.


    Marsden Group SOHO comets
    2011 Cn (SOHO)(IAUC )
    were discovered with the SOHO LASCO coronographs and have not been observed elsewhere. They were sungrazing comets of the Marsden group.

    Rainer Kracht suggests that the comet discovered by Rob Matson on February 15 (SOHO-2024) may be a return of either 2005 W1 or 2005 W5, with the latter slightly more likely, but still giving large residuals. Further investigation by Rainer suggested that there is a promising link between the comet and 1995 N5 and 2005 G2, though this required non gravitational forces. This would be the second three apparition linkage of a Marsden comet.

    On 2011 July 17 Alan Watson reported a Marsden group comet in real time C3 images. Rainer Kracht computed an orbit and then linked the object to 2000 C4 == 2005 W1. A non-gravitational parameter was required to match the perihelion dates.

    Karl Battams has put together a probable family tree for the fragments.

    For further information on the discovery of these objects see this year's SOHO discoveries.


    SOHO Kreutz group comets
    2011 N3 (SOHO)(IAUC )
    were discovered with the SOHO LASCO coronographs and have not been observed elsewhere. They were sungrazing comets of the Kreutz group and were not expected to survive perihelion. Some of these comets show no tail at all and it is possible that some supposed observations of Vulcan were actually tiny Kreutz group comets. This particular comet was caught by the SDO AIA instrument. Details of the SOHO Kreutz comets discovered or announced this year are listed here, with an abbreviated list here.
    2011 A1 (250P/Larson)
    A 19th magnitude comet was discovered by Steve Larson on Catalina Sky Survey images taken with the 0.68-m Schmidt telescope on January 10.44. Confirming images were taken with the Mt. Lemmon 1.5-m reflector and also following posting on the NEOCP. The comet has a period of 7.3 years and was at perihelion at 2.2 AU in 2010 November.

    Images of the comet were found in Spacewatch images from 1995 and 2004 (identified by S Nakano) and NEAT images from 2002 (identified by Maik Meyer). The comet was then numbered.


    2011 A2 (P/Scotti)
    Jim Scotti discovered a 20th magnitude comet in Spacewatch images taken with the 0.9-m f/3 reflector at Kitt Peak on January 11.46. The preliminary orbit suggests that the comet was near perihelion at 1.8 AU.

    Gareth Williams notes on MPEC 2011-A65 [2011 January 14] that it is probable that this is a short-period comet and that further [astrometric] observations of this comet are desirable.

    Further observations confirm the short period orbit, and Hirohisa Sato gives a period of around 6.5 years with perihelion at 1.6 AU in 2010 December.


    2011 A3 (Gibbs)
    Alex Gibbs discovered an 18th magnitude comet on Catalina Sky Survey images taken with the 0.68-m Schmidt telescope on January 15.51. The comet was at perihelion at 2.3 AU in December.   Visual observers picked up the comet in August when it was already 11th magnitude and it was about 10th magnitude as it headed towards conjunction in October.

    9 observations received so far suggest a preliminary light curve of m = -3.9 + 5 log d + 28.6 log r, though this is likely to change once the comet is recovered after conjunction.


    2011 A4 (249P/LINEAR)
    Leonid Elenin (Lyubertsy, Russia) recovered 2006 U1 (P/LINEAR) using the ISON-NM Observatory near Mayhill, New Mexico, USA. The indicated correction to the prediction by S. Nakano (2010/2011 Comet Handbook) is Delta(T) = +0.24 day.
    A/2011 AF3 [Catalina]
    This unusual asteroid was discovered by the Catalina Sky Survey with the 0.68m Schmidt on January 4.38. It has a period of 19 years and perihelion is at 0.39 AU in mid February 2011. [MPEC 2011-A18, 2011 January 4, 0.05-day orbit]. In the current orbit it can approach to around 0.4 AU of Jupiter and 0.01 AU of the Earth. Aphelion is at 13.6 AU. The orbit has a Tisserand criterion of 1.50 with respect to Jupiter. The object is very small, with an absolute magnitude of 25.1. It was found around the time of closest approach whilst almost at opposition.
    A/2011 BX59 [PanSTARRS]
    This unusual asteroid was discovered by the Pan-STARRS 1 1.8m Ritchey-Chretien reflector on January 30.47. It has a period of 5 years and perihelion is at 1.05 AU in mid March 2011. [MPEC 2011-D12, 2011 February 19, 8-day orbit]. In the current orbit it can approach to around 0.4 AU of Jupiter and 0.07 AU of the Earth. The orbit has a Tisserand criterion of 2.94 with respect to Jupiter.
    2011 C1 (McNaught)
    Rob McNaught discovered a 17th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on February 10.72. The comet will reach perihelion inside the Earth's orbit in mid April. Calculations by Hirohisa Sato suggest that the comet is in a very long period orbit.

    The comet has brightened rapidly as it approached perihelion and reached 11th magnitude by the equinox. It will brighten a little further, but never becomes well placed for viewing from the UK. Despite the rapid initial brightening, the overall curve has a rather low magnitude parameter.

    34 observations received so far suggest a preliminary light curve of m = 9.4 + 5 log d + 4.3 log r


    2011 C2 (P/Gibbs)
    Alex Gibbs discovered a 20th magnitude comet on February 12.29 on CCD images taken with the Mt Lemmon 1-5m reflector. The comet has a period of around 20 years and reaches perihelion at 5.4 AU in 2012 January.
    2011 C3 (Gibbs)
    Alex Gibbs discovered a second comet on February 12.50. It was also of 20th magnitude. It is due to reach perihelion at 1.5 AU in early April. Calculations by Hirohisa Sato suggest that a long period orbit.
    2011 CR42 (P/Catalina)
    This main belt asteroid was discovered by the Catalina Sky Survey with the 0.68m Schmidt on February 10.47 and was followed until June. Hints of cometary activity were given on a CBET that was issued on 2011 September 23. It was at perihelion at 2.5 au in 2011 November, but was then poorly placed for observation.

    Cometary activity was finally confirmed in 2013, when it was observed from August to October. [MPEC 2013-U85, 2013 October 30]. The comet has a period of 6.6 years.


    A/2011 ED78 [Mt Lemmon]
    This unusual asteroid was discovered by the Mt Lemmon Survey with the 1.5m reflector on March 9.38. It has a period of 5.9 years and perihelion is at 1.19 AU in early August 2011. [MPEC 2011-G02, 2011 April 1, 22-day orbit]. In the current orbit it can approach to around 0.3 AU of Jupiter and 0.2 AU of the Earth. Aphelion is at 5.3 AU. The orbit has a Tisserand criterion of 2.81 with respect to Jupiter.
    2011 F1 (LINEAR)
    LINEAR discovered an 18th magnitude object on March 17.28, which was seen to show a coma by astrometrists, including Peter Birtwhistle, Roger Banks and other European based observers. The comet was over 7 AU from the Sun at discovery and does not reach its 1.8 AU perihelion until January 2013, when it may be around 10th magnitude.  Visual observations in the first half of 2012 show it brightening to around 11th magnitude.  UK observers will loose it in 2012 October.  

    93 observations received so far suggest a preliminary light curve of m = 6.0 + 5 log d + 6.9 log r


    2011 FR143 (P/Lemmon)
    An object discovered during the Mt Lemmon Survey with the 1.5m reflector on 2011 March 29.41 was given an asteroidal designation, though the orbit was quite unusual. It was therefore added to the T3-observing project and almost exactly a year later Luca Buzzi and Sergio Foglia observed it from the "G.V.Schiaparelli" Astronomical Observatory in Italy. He noted a coma and tail, which was quickly confirmed by other observers. The comet has a period of nearly 18 years and was at perihelion at 3.7 AU in 2011 March.
    2011 G1 (McNaught)
    Rob McNaught discovered a 17th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on April 5.74. The comet reached perihelion at 2.2 AU in September.
    A/2011 GO44 [Catalina]
    This unusual asteroid was discovered by the Catalina Sky Survey with the 0.68m Schmidt on April 5.35. It has a period of 5.6 years and perihelion was at 1.32 AU in mid March 2011. [MPEC 2011-G47, 2011 April 6, 1-day orbit]. In the current orbit it can approach to around 0.5 AU of Jupiter and 0.4 AU of the Earth. The orbit has a Tisserand criterion of 2.88 with respect to Jupiter. It was found around the time of its closest approach to the Earth whilst almost at opposition.
    2011 H1 (Mt Lemmon) = 2002 VQ94 (LINEAR)
    Alex Gibbs reported an asteroidal object of 20th magnitude discovered at Mt Lemmon on April 26.30, which he suspected might show some diffuseness. Subsequent images by astrometrists also showed a slightly diffuse object. MPEC 2011-H41 was issued on April 28, and gave the object the designation 2011 GK71 [An orbit with a 200 year period and perihelion at 7 AU with an inclination of 63 degrees, which I had noted as unusual, but which did not appear to show any planetary encounters]. Further deep astrometry showed a very faint tail and the object was designated 2011 H1 on May 5. The comet was at perihelion in 6.9 AU in 2006 January. The initial orbit is parabolic. The discovery was announced in IAUC 9206, which gives a not altogether clear account of the sequence of events.

    These problems were compounded on May 14, when Hidetaka Sato noted the similarities of the orbit with that of 2002 VQ94 (LINEAR), which had last been observed in October 2010. The comet was at perihelion at 6.8 AU in 2006 February and has a period of around 2500 years.

    On IAUC 9209 [2011 May 20] Dan Green notes "The name associated with C/2011 H1 on IAUC 9206 is being abandoned, due to the belated identification of this comet."


    2011 J1 (251P/LINEAR)
    Jim Scotti recovered 2004 HC18 (P/LINEAR) using the Spacewatch 1.8m reflector on May 1.47. The indicated correction to the prediction in the 2010/2011 Comet Handbook) is Delta(T) = -0.10 day.
    2011 J2 (LINEAR)
    LINEAR discovered a 20th magnitude object on May 4.19, which was seen to show a coma by astrometrists, including several amateur observers. The comet was over 8 AU from the Sun at discovery and does not reach its 3.4 AU perihelion until December 2013.  In 2014 September a secondary condensation was observed by several astronomers.  Zdenek Sekanina calculates that the nucleus split around two weeks after perihelion.

    10 visual and electronic observations received so far suggest a preliminary light curve of m = 5.1 + 5 log d + 9.5 log r


    2011 J3 (LINEAR)
    LINEAR discovered a 20th magnitude object on May 14.38, which was seen to show a coma by astrometrists, including several amateur observers. The comet is in a Halley-type retrograde orbit of around 75 years and was at perihelion at 1.4 AU in January.
    2011 JB15 (P/Spacewatch-Boattini)
    Andreas Boattini discovered a 19th magnitude comet on images obtained with the Mt Lemmon 1.5m reflector on May 28.33. After posting on the NEOCP the comet was identified with an apparently asteroidal object imaged by Spacewatch on May 8.39 and May 12. Follow up observations by other astrometrists confirmed the cometary nature. The comet has a period of around 20 years and was at perihelion at 5.0 AU in 2012 January.
    2011 K1 (Schwartz-Holvorcem)
    Michael Schwartz and Paulo Holvorcem discovered a comet in co-added images begun on May 26,26 taken with the Tenagra III 0.41-m astrograph. Other astrometrists confirmed the cometary nature. The comet is near perihelion at 3.4 AU.
    2011 KP36 (Spacewatch)
    This unusual asteroid was discovered at the Steward Observatory, Kitt Peak with the Spacewatch 0.9m reflector on 2011 May 21.33. It has a period of around 240 years and perihelion is at 4.9 AU in 2016 May. [MPEC 2011-L56, 2011 June 14; MPEC 2012-F43, 2012 March 19, MPEC 2012-K12, 2012 May 17]. The aphelion distance is nearly 100 AU. The orbit has a Tisserand criterion of 2.64 with respect to Jupiter and the object can pass within 0.3 AU of the planet.

    In May 2012 cometary features were detected by chance by Tomas Vorobjov, with follow-up observations by Sergei Foglia, Luca Buzzi (as described by Luca) and the object was then given a cometary designation.


    2011 L1 (McNaught)
    Rob McNaught discovered a 17th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on June 2.63. The comet was at perihelion at 2.4 AU in January.
    2011 L2 (McNaught)
    Rob McNaught discovered a 18th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on June 2.78. The comet reached perihelion at 1.9 AU in November.
    2011 L3 (McNaught)
    Rob McNaught discovered a 16th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on June 3.77. The comet reached perihelion at 1.9 AU in August.  A few visual observations between July and September suggest it was around 13 to 14 magnitude.
    2011 L4 (PanSTARRS)
    Richard Wainscoat, Institute for Astronomy, University of Hawaii, reported to the MPC that an object discovered on four CCD images taken with the 1.8-m "Pan-STARRS 1" telescope at Haleakala on June 6.39 appeared to show slight non-stellar appearance; three follow-up 30-s r-band exposures were then acquired by M. Micheli and Wainscoat with the Canada-France-Hawaii Telescope on Mauna Kea (queue observer Lisa Wells) on June 7.44 UT, showing that a coma is definitely visible with a subtle hint of a faint tail towards p.a. 60 deg. After posting on the NEOCP astrometrists confirmed the cometary nature. [IAUC 9215, 2011 June 8]. The preliminary orbit gave perihelion at 0.4 AU in March 2013, however the accuracy quoted in the IAUC was rather great for the short arc of only 15 days.  The comet has perihelion at 0.3 AU in 2013 March.  The comet could be a naked eye object from the UK in March 2013. 

    Visual observations began in 2012 March, when the comet was a stellar 14th magnitude, but by May it had developed a coma, and it was around 12th magnitude by mid year. It continued brightening relatively quickly and by September was 10th magnitude. Some observers reported an outburst in August, but this was not apparent in the mean light curve.  

    It was recovered after solar conjunction on December 24.3 by Alexander Amorim, when it was 8.1 in his 0.18m reflector.  It soon became clear that the rate of brightening had slowed.  By 2013 February it had reached 5th magnitude.  It continued brightening and by the end of the first week of March had reached 0th magnitude according to observations by Marco Goiato.  The comet was first observed from southern England on March 12.  I observed it from central Cambridge on March 13, when it was around 0th magnitude, with a 15' tail in 8x42B.  Clouds and cold temperatures prevailed for much of March, but on the 28th they parted for a short while at just the right time permitting a view of the comet from a nearby Common.  In 8x42B it was 4.3, with a 1 tail in pa 020.

    Nicolas Biver comments that it is one of the dustiest comets observed, with disproportionately high dust compared to its water vapour sublimation rate.

    231 observations received to April 30 suggested an aperture corrected preliminary light curve of m = 4.6 + 5 log d + 6.9 log r , however there is some evidence for a change in photometric behaviour when the comet was in solar conjunction between 2012 October 22 and 2012 December 24.  After this period the data is fitted by m = 5.4 + 5 log d + 9.5 log r , with the data prior to this period being about 2 magnitudes brighter than the curve.

    Note that a light curve only says how a comet has behaved - there is no guarantee that it will continue to behave in the same way.  

    Uwe Pilz generated a simulation of the possible tail appearance


    2011 L5 (252P/LINEAR)
    Jim Scotti recovered comet 2000 G1 (P/LINEAR) with the Spacewatch telescope on June 9.42, when it was 23rd magnitude. It was not recovered at its previous return in 2005. The most recemt perihelion was in November 2010. The indicated correction to the prediction on MPC 59601 is Delta(T) = -0.24 day.
    2011 L6 (Boattini)
    Andrea Boattini discovered a 20th magnitude comet in Mt Lemmon survey images taken on June 8.22. The comet was at perihelion in January at 6.8 AU.
    2011 M1 (LINEAR)
    LINEAR discovered a 19th magnitude asteroidal object on June 22.38, which was seen to show a coma by many amateur astrometrists, including Peter Birtwhistle and other European based observers. The comet was at perihelion at 0.9 AU in September, but was not particularly well placed for observation. It brightened from 13th magnitude in July to reach 9th magnitude by the time it was lost in September.
    A/2011 MT [Mt Lemmon]
    This unusual Amor asteroid was discovered by the Mt Lemmon Survey with the 1.5m reflector on June 22.35. [MPEC 2011-M33, 2011 June 25, 3-day orbit]. It has a period of 5.4 years and perihelion was at 1.30 AU in early June 2011. In the current orbit it can approach to within 0.5 AU of Jupiter and 0.3 AU of the Earth. The orbit has a Tisserand criterion of 2.93 with respect to Jupiter.
    A/2011 MC2 [Mt Lemmon]
    This unusual asteroid was discovered by the Mt Lemmon Survey with the 1.5m reflector on June 25.43. It has a period of 6.9 years and perihelion is at 1.31 AU in early July 2011. [MPEC 2011-43, 2011 June 27, 2-day orbit]. In the current orbit it can approach to within 0.1 AU of Jupiter. The orbit has a Tisserand criterion of 2.71 with respect to Jupiter.
    2011 N1 (P/ASH)
    Ignacio de la Cueva, Ibiza, Spain reported an asteroidal object on exposures taken by J. L. Ortiz, P. Santos-Sanz, N. Morales, and himself with a 0.40-m f/3.7 reflector at San Pedro de Atacama, Chile on July 1.36. Follow up images taken on July 3.4 and 4.4 UT, by de la Cueva, Morales, and Ortiz with a 0.45-m reflector at Cerro Burek (Chile) showed a tail extending about 10" and one of 55" in the anti-solar direction. Following posting on the NEOCP other observers confirmed the cometary nature. The comet is in a short period orbit of about 16 years and reaches perihelion at 2.9 AU in 2012 May.
    2011 N2 (McNaught)
    Rob McNaught discovered a 18th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on July 4.46. The comet reached perihelion at 2.6 AU in October.
    2011 NO1 (P/Elenin)
    An orbit for an unusual minor planet discovered by Leonid Elenin on July 3.0 using the remote 0.45m astrograph at ISON-NM Observatory, Mayhill, USA was published on MPEC 2011-O09 on July 18. The next MPEC published the following day gave a cometary designation. The object was at perihelion at 1.2 AU in January and has a period of about 13 years.
    2011 O1 (LINEAR)
    LINEAR discovered an 18th magnitude object on July 31.16, which was seen to show a coma by astrometrists. The comet reaches its 3.9 AU perihelion in 2012 August.
    A/2011 OR17 [Siding Spring]
    This unusual asteroid, a Cubewano or Scattered Disk Object, was discovered by the Siding Spring Survey with the 0.5m Uppsala Schmidt on July 29.50.[MPEC 2011-O62, 2011 July 30, 1-day orbit].  It has a retrograde orbit with a period of nearly 6000 years and perihelion was at 3.1 AU in August. In the current orbit it can approach to within 1.1 AU of Saturn. The orbit has a Tisserand criterion of -0.14 with respect to Jupiter.
    2011 P1 (P/McNaught)
    Rob McNaught discovered a 17th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on August 1.77. The preliminary elements were given to unreasonable precision given that Gareth Williams noted on MPEC 2011-P19 [2011 August 4]
    From 12 observations 2011 August 1-4. Very uncertain elements, continuing observation very desirable.
    Gareth further noted on MPEC 2011-Q34 [2011 August 26]
    The orbit for P/2011 P1 (McNaught) is given for the current standard epoch (2011 August 27.0 TT) rather than the traditional 40-day-epoch closest to the date of perihelion passage. This is due to the close approach (within 0.025 AU) that the comet had with Jupiter in 2010 December. Prior to this encounter (and based on the nominal orbit above), the comet was in an 11.8-year orbit with q = 3.9 AU, Incl = 5 deg and T = 2013 March.
    The current orbit has a period of 21 years with perihelion at 5.0 AU in 2010 July. Gareth Williams provides more background in The Daily Minor Planet
    2011 P2 (PanSTARRS)
    Pan-STARRS discovered a 21st magnitude comet on August 3.39. It was at perihelion at 6.1 AU in 2010 September and has a period of around 30 years.
    2011 Q1 (PanSTARRS)
    Pan-STARRS discovered a 21st magnitude comet on August 20.44. It was at perihelion at 6.8 AU in 2011 June.
    2011 Q2 (McNaught)
    Rob McNaught discovered a 15th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on August 26.40. The comet reaches perihelion at 1.3 AU in 2012 January. It is poorly placed at perihelion and may not get brighter than 13th magnitude.
    2011 Q3 (P/McNaught)
    Rob McNaught discovered a 19th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on August 29.74. The comet reached perihelion at 2.4 AU in August and has a period of 11 years.
    2011 Q4 (SWAN)
    Rob Matson and Vladimir Bezugly reported an object in SWAN imagery, which was then confirmed as a comet by Rob McNaught and Michael Mattiazzo. The comet was at perihelion at 1.1 AU near the September equinox. Although the comet was still approaching the Sun at discovery, it was receding from the Earth and expected to fade. Its discovery magnitude was 13, though visual observers made it a couple of magnitudes brighter. A few visual observations have continued into December, but do not produce a consistent light curve.  It has a long period orbit.
    A/2011 QD23 [ISON-NM]
    This asteroid was discovered with the ISON-NM Observatory, Mayhill 0.45m f/2.8 astrograph by Leonid Elenin on August 25.30.  [MPEC 2011-Q39, 2011 August 27]. It has a period of 4.1 years and perihelion was at 1.58 AU in late September 2011.  The orbit has a Tisserand criterion of 3.32 with respect to Jupiter.  This is not particularly unusual, and the asteroid was only listed on the basis of the preliminary orbit. 
    2011 R1 (McNaught)
    Rob McNaught discovered a 17th magnitude comet on CCD images taken with the 0.5-m Uppsala Schmidt telescope at Siding Spring on September 3.72. The comet reached perihelion at 2.1 AU in 2012 October, when it was around 11th magnitude.  It will begin to fade in April.

    32 observations received so far suggest a preliminary light curve of m = 5.9 + 5 log d + 10.5 log r


    2011 R2 (253P/PanSTARRS)
    Pan-STARRS discovered a 19th magnitude comet on September 4.51. It will be at perihelion at 2.0 AU in November.

    Subsequently S Nakano was able to identify the comet with LINEAR images of asteroid 1998 RS22 and then with 2005 observations by Spacewatch. The comet has a period of 6.5 years.


    2011 R3 (P/Novichonok-Gerke)
    MPEC 2011-R34 announced the discovery by Artyom Novichonok of a comet with the 0.4-m f/8 Ritchey-Chretien at Ka-Dar Observatory, TAU Station, Nizhny Arkhyz on images taken on September 7.02 by Vladimir Gerke. The comet has a period of 11 years with perihelion at 3.6 AU in 2012 April.

    Only the name Novichonok was originally given to the comet, however the discoverer was clear that it was a team effort with Gerke, and the name was later amended.

    Denis Denisenko notes

    As usual, there's a whole story behind the new discovery. This comet was caught just 63 (!!!) pixels from the edge of 1330x890 CCD image in 3x3 binning mode in the first night. Upon posting at NEO Confirmation Page most people (including myself) originally thought it to be identical to 111P (whose predicted position was less than 5' away, yet the magnitude was almost identical to the new object). But the direction of motion of the Comet Novichonok was totally different from Comet Helin-Roman-Crockett, and the new object was about twice slower.

    Congratulations to Artyom with the first Russian periodic comet since the breakup of USSR! If you remember, two Comets Elenin were discovered on the telescope installed in USA. This time the observation was made in southern Russia, in the Republic of Karachay-Cherkessia in northern Caucasus, not far away from the 6-meter BTA telescope.


    2011 S1 (P/Gibbs)
    Alex Gibbs discovered a 21st magnitude comet on September 18.27 on CCD images taken with the Mt Lemmon 1-5m reflector. The comet reaches perihelion at 6.8 AU in 2014 October and has a period of around 25 years.
    2011 S2 (Kowalski)
    A 17th magnitude comet was discovered by the Catalina Sky Survey on September 30.48. Gareth Williams notes on MPEC 2011-T12 [October 2]
    The orbit of this object is essentially indeterminate at the present time. It is possible that this is a short-period comet. Among the wide range of possible short-period orbits are orbits that appear similar to P/2006 T1 (Levy). Initial attempts to link the two apparitions have not been successful. Further observations are encouraged.
    Further observations show that the comet was at perihelion at 1.1 AU in late October and has a period of around 65 years.  A couple of visual observations in October suggested that the comet was a little fainter than 11th magnitude.
    A/2011 SP25 [PanSTARRS]
    This unusual asteroid was discovered by the Pan-STARRS 1 1.8m Ritchey-Chretien reflector on September 20.52. [MPEC 2011-S45, 2011 September 22, 2-day orbit]. It has a retrograde orbit with a period of nearly 90 years and perihelion was at 2.3 AU in November 2011. Aphelion is at 37 AU. The orbit has a Tisserand criterion of -0.12 with respect to Jupiter.
    2011 U1 (P/PanSTARRS)
    Pan-STARRS discovered a 21st magnitude comet on October 23.45. It will be at perihelion at 2.4 AU in June 2012 and has a period of around 8.1 years.  Maik Meyer has located NEAT images of the comet from 2004 February, so the comet should be numbered once a linked orbit is computed.  This may be waiting on additional Spacewatch images, as an orbit based on observations from 2004 to 2012 was published in MPC 78186 in 2012 February..
    2011 U2 (P/Bressi)
    Terry H Bressi discovered a 19th magnitude comet in Spacewatch images taken with the 0.9-m f/3 reflector at Kitt Peak on October 24.21. The comet will reach perihelion at 4.8 AU in May 2012 and has a period of around 13 years.
    2011 U3 (PanSTARRS)
    Pan-STARRS discovered a 22nd magnitude comet on October 24.54. It will be at perihelion at 1.1 AU in June 2012. Based on the discovery magnitude the comet will become no brighter than 14th magnitude, however it remains to be seen how much coma it will actually generate.
    2011 UA134 (P/Spacewatch-PanSTARRS)
    A 20th magnitude asteroid discovered by Spacewatch on October 24.43 was reported by Pan-STARRS as a 21st magnitude comet on October 25.43. It was at perihelion at 2.1 AU in December and has a period of around 13 years. This is the 50th discovery for Spacewatch.
    A/2011 UF256 [Mt Lemmon]
    This unusual Amor asteroid was discovered by the Mt Lemmon Survey with the 1.5m reflector on October 30.44.  [MPEC 2011-U117, 2011 October 31, 1-day orbit]. It has a period of 7.6 years and perihelion was at 1.2 AU in late November 2011.In the current orbit it can approach to around 0.4 AU of Jupiter and 0.3 AU of the Earth. The orbit has a Tisserand criterion of 2.31 with respect to Jupiter.
    2011 UF305 (LINEAR)
    This comet, originally classed as an unusual asteroid, a Cubewano or Scattered Disk Object, was discovered by LINEAR on October 31.08 with the 1-0m reflector.  [MPEC 2011-V16, 2011 November 3, 3-day orbit]. The slightly retrograde high inclination orbit has a very long period and perihelion is at 2.1 AU in 2012 July.  Aphelion is at over 2000 AU. The orbit has a Tisserand criterion value of 0.13.

    As seemed possible from the orbit, the object eventually showed cometary characteristics, and was reclassified as a comet with an orbit published on MEPC 2011-Y51 [2011 December 28].

    The comet reached around 11th magnitude around the time of perihelion.

    19 observations received so far suggest a preliminary light curve of m = -3.9 + 5 log d + 37.8 log r


    A/2011 UR402 [PanSTARRS]
    This unusual asteroid was discovered by the Pan-STARRS 1 1.8m Ritchey-Chretien reflector on October 23.45. [MPEC 2011-X23, 2011 December 5, 40-day orbit].  It has an orbit with a period of around 80 years and perihelion is at 4.1 AU in May 2014. Aphelion is at 34 AU. The orbit has a Tisserand criterion of 2.44 with respect to Jupiter.
    2011 V1 (P/Boattini)
    Andrea Boattini discovered a 19th magnitude comet in Mt Lemmon survey images taken on November 1.30 and was then able to find pre-discovery images from October 22. The comet was at perihelion in May at 1.7 AU and has a period of around 7.5 years.
    2011 VJ5 P/Lemmon
    This object was discovered as an asteroid by the Mt Lemmon Survey with the 1.5m reflector on November 3.46. There was nothing particularly unusual about the preliminary orbit. Cometary characteristics were detetected by the Catalina Sky Survey on 2012 February 1.47, and the new orbit gives the comet a period of 6.2 years with perihelion at 1.5 AU in 2011 December.
    2011 W1 (P/PanSTARRS)
    Pan-STARRS discovered a 19th magnitude comet on November 26.54. It was at perihelion at 3.3 AU in January 2012 and has a period of around 10 years.
    2011 W2 (P/Rinner)
    Amateur observer Claudine Rinner discovered a comet from Oukaimeden Observatory, near Marrakech, Morocco on November 28.13 on CCD images taken by herself and Michel Ory with the 0.5-m f/3 reflector. The comet was at perihelion at 2.3 AU in November and has a period of around 7.4 years.
    2011 W3 (Lovejoy)
    Terry Lovejoy discovered an object on November 27.73, which was posted on the NEOCP as TLc001. As astrometry accumulated it became clear that it might be a Kreutz comet, and this was confirmed on December 2, when MPEC 2011-X16 gave a retrograde orbit with perihelion at 0.006 AU on December 16.0. The comet is intrinsically faint, and John Bortle opined that it would not survive perihelion. Orbit calculations by Hirohisa Sato suggest a periodic orbit, though I suspect that the period is not yet well determined. The comet looks as if it belongs to the group Kreutz I.  The consensus seems to be that this was the largest of the small sungrazers yet seen by SOHO.

    SOHO observations suggested that the comet reached a peak of around -4, but began fading before perihelion. It showed two tails, which were probably ion (or iron) and dust tails. SDO observations show that it survived perihelion, racing through the solar corona.  It then re-emerged into the SOHO field, brighter but minus the tail, which lagged behind on the other side of the sun.  It was imaged by Terry Lovejoy during daylight on December 17.0, when he estimated it at -1.2.  A visual observation by Alexandre Amorim on December 17.34 put the comet at -2.9. Marco Gioato observed it at 2.8 on December 22.3.  There have been many spectacular images of the tail taken from the Southern Hemisphere.  The comet will  be largely a Southern Hemisphere object.    Details of the SOHO story.

    The absolute magnitude of the comet was some 5 magnitudes brighter post-perihelion than it was pre-perihelion. A likely explanation is that a part of the comet's surface was inactive prior to perihelion, and that as the nucleus rotated through the solar atmosphere the inert surface was eroded away, exposing fresh material. It is possible that as the comet recedes from the Sun, parts of the fresh surface will choke off, resulting in a relatively quick fading.

    Terry provided the following background on the comets-ml

    Anyway to the discovery of C/2011 W3, it was the first comet I have found with my new equipment setup. I now use a C8 Schmidt-Cassegrain scope working at f2.1 with a QHY9 CCD camera. This gives me a field of view of a 4.5 square degrees which although only 1/8th of that of my previous DSLR camera, more than makes up for this in extra sensitivity. As a result I can cover the same amount of sky to perhaps a magnitude deeper. Despite this it has been over 4 years since my last discovery and I do hope the next one comes a lot sooner!

    The actually discovery images of W3 were made on November 27.7UT, 2011 (Wednesday morning local time). On that morning I imaged some 200 different fields with 3 images each, taking about 2 hours to fully process. After processing, I began searching and on one set of images I noticed a rapidly moving fuzzy object. As I was unsure this was real, I noted the positions and wrote a brief comment "Possible reflection" before proceedind to search more images. The next night I decided to investigate further the suspect since its position, shape and motion didn't appear consistent with an optical reflection and for this reason I decided to make a followup observation.

    On November 29.7 UT I began an imaging sequence around the estimated position of the object. However, if the object was real it was travelling very rapidly at 3 degrees per day so any uncertainty in the direction and speed would mean the estimated position could be in error by a couple of degrees. Furthermore cloud and haze hampered imaging that morning. Nonetheless, I was able to capture 6 images that showed a faint but definite fuzzy object near the expected position. Additionally the fuzzy object was consistent in both motion and appearance to the object found 2 mornings earlier. At this point I sent out a request for independent confirmation to a number of trusted observers.

    On November 30, all recovery attempts were thwarted for many reasons including weather and insufficient limiting magnitude. Interestingly though, Michael Mattiazzo made a comment that he felt the observed positions were similiar to that of a Kreutz sungrazer. Then, finally, on December 1 I recieved an email from Alan Gilmore stating that he and Pam Kilmartin had successfully imaged the comet with the 1 metre telescope at Mt John Observatory. A few hours later I also managed to get some followup images. The object was then published on the NEO confirmation page before being susequently officially announced in CBET 2930/2931 on December 2.

    Gareth Williams notes on MPEC 2011-Y16 [2011 December 22]
    Although a new orbit is being published, the December 19 STEREO observations were within about 1' of the previously-published orbit. The new observations were weighted 0.1 in the above orbit. Resolution of the issues surrounding the STEREO astrometry will probably have to await the acquisition of further ground-based astrometry.
    Gareth Williams notes on MPEC 2011-Y23 [2011 December 25]
    C/2011 W3 remains a difficult target for astrometry, as evidenced by the poor consistency of the latest observations. McNaught writes: "Star fit RMS 0.3", but measures are much less reliable than that. The positions are of the tip of the "spine" which lies pretty much on the front edge of the parabolic hood. It is rather less well defined than on Dec 23. For this reason I cannot be sure just how closely I am measuring the same point as on Dec 23."
    Sergei Schmalz reports from the Asteroids Comets Meteors 2012 conference held in Niigata, Japan in 2012 May:
    A presentation "A Multiwavelength Investigation of the Remains of the Sungrazing Comet Lovejoy (C/2011 W3)", was given by Matthew Knight. You can fread the abstract (PDF). It was interesting to see images of the comet's remains obtained by Hubble, Swift and Spitzer telescope, showing the absence of the nucleus and lots of dust.

    12 observations received to January 4 suggest a preliminary light curve of m = 10.8 + 5 log d + 15.8 log r


    A/2011 WS41 [PanSTARRS]
    This unusual asteroid was discovered by the Pan-STARRS 1 1.8m Ritchey-Chretien reflector on November 24.47. [MPEC 2011-W58, 2011 November 26, 1-day orbit].  It has a retrograde orbit with a period of around 20 years and perihelion was at 1.9 AU in June. The orbit has a Tisserand criterion of -0.57 with respect to Jupiter.
    A/2011 XO3 [Catalina]
    This unusual asteroid was discovered by the Catalina Sky Survey with the 0.68m Schmidt on December 1.28. It has a period of 5.8 years and perihelion is at 1.10 AU in April 2012. [MPEC 2012-A41, 2012 January 9, 1-month orbit]. In the current orbit it can approach to within 0.5 AU of Jupiter and 0.16 AU of the Earth. The orbit has a Tisserand criterion of 2.69 with respect to Jupiter.
    2011 Y1 (255P/Levy)
    P/2006 T1 was recovered by the Mt Lemmon Survey on December 17.06 and quickly confirmed by other astrometrists, including Peter Birtwhistle and Richard Miles. At 18th magnitude the comet is much fainter than expected (10 magnitudes) and 2.6 days from the expected perihelion. It was clearly in outburst at discovery in 2006, and there is always a chance that there will be repeat at this return. Unless this happens, or the light curve is unusual it will not get within visual range.
    2011 Y2 (P/Boattini)
    Andrea Boattini discovered a 19th magnitude comet in Mt Lemmon survey images taken on December 24.13 and was then able to find pre-discovery images from October 30. Further images from Spacewatch on October 16 and PanSTARRS on September 4 allowed a good preliminary orbit. The comet will be at perihelion in 2012 March at 1.8 AU and has a period of around 16 years.
    2011 Y3 (Boattini)
    Andrea Boattini discovered a 19th magnitude comet in Mt Lemmon survey images taken on December 25.24. The comet was at perihelion at 3.5 AU in August. 
    A/2011 YQ15 [Mt Lemmon]
    This unusual asteroid was discovered by the Mt Lemmon Survey with the 1.5m reflector on December 25.14.  [MPEC 2011-Y43, 2011 December 28, 3-day orbit]. It has a period of 5.7 years and perihelion is at 1.3 AU in March 2012. In the current orbit it can approach to within 0.3 AU of Jupiter. The orbit has a Tisserand criterion of 2.91 with respect to Jupiter.
    A/2011 YU75 [Steward Observatory]
    This unusual asteroid was discovered at the Steward Observatory, Kitt Peak with the 0.9m reflector on December 26.46. It has a period of around 20 years and perihelion is at 1.7 AU in late April. [MPEC 2012-C41, 2012 February 11, 46-day orbit]. The orbit has a Tisserand criterion of 2.17 with respect to Jupiter. The object has made no recent close approaches to Jupiter.
    Ephemerides of current comets are available on the CBAT ephemeris page and positions of newly discovered comets are on the NEO 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.
    Published by Jonathan Shanklin. Jon Shanklin - jds@ast.cam.ac.uk