Comet Prospects for 2006

 

2006 sees the possible return of 26 periodic comets and several of these are likely to come within range of visual observation with moderate apertures.  Potentially, the most exciting is the close passage of 73P/Schwassmann-Wachmann in May.

 

Theories on the structure of comets suggest that any comet could fragment at any time, so it is worth keeping an eye on some of the fainter periodic comets, which are often ignored.  This would make a useful project for CCD observers.  As an example 51P/Harrington was observed to fragment in 2001.  Ephemerides for new and currently observable comets are published in the Circulars, Comet Section Newsletters and on the Section, CBAT and Seiichi Yoshida's web pages.  Complete ephemerides and magnitude parameters for all comets predicted to be brighter than about 21m are given in the International Comet Quarterly Handbook; details of subscription to the ICQ are available from the comet section Director.  The updated section booklet on comet observing is available from the BAA office or the Director.

 

Hervé A Faye discovered 4P/Faye in 1843 during a visual search with a small telescope at the Paris Observatory.  It reached 5m, though this has never been reached at subsequent returns.  It is possible that this was a one off caused by a slight reduction in perihelion distance from 1.8 to 1.7 AU following a close encounter with Jupiter in 1841.  Several authors have suggested that the absolute magnitude of the comet is declining rapidly, but it reaches a similar magnitude at all favourable apparitions.  This return is very similar to the 1991 return, when it reached 10th magnitude.  We should be able to pick it up in the morning sky in July, and it reaches opposition on the border of Cetus and Pisces in late October.  It is at its brightest in early November and slowly fades.

 

29P/Schwassmann-Wachmann is an annual comet that has outbursts, which in recent years seem to have become more frequent and were more or less continuous in 2004.  At many recent outbursts it has reached 12m.  It spends the first half of the year in Aries, reaching opposition in late November as it retrogrades on the borders of Taurus and Perseus.  The comet is an ideal target for those equipped with CCDs and it should be observed at every opportunity.  It is well placed this year and UK based observers should be able to follow it until the end of March, and it should be possible to recover it again in July.

 

Horace Tuttle was the first discoverer of 41P/Tuttle-Giacobini-Kresak in 1858, when he found a faint comet in Leo Minor.  Nearly 50 years later, Professor Michael Giacobini discovered a 13m object whilst comet hunting, which was observed for a fortnight.  Andrew C D Crommelin linked the apparitions in 1928 and made predictions for future returns, but the comet wasn't recovered and it was given up as lost.  In 1951, Lubor Kresak discovered a 10m comet in 25x100 binoculars whilst participating in the Skalnate Pleso Observatory's program of routine searches for comets.  After further observations the comet was identified with the lost comet and a better orbit computed.  At the 1973 return, which was similar to the 1907 return, it underwent a major outburst and reached 4m, before fading and then undergoing a second outburst.  Alternate returns are favourable and this, its 10th, is one of them.  At the last two returns the comet has reached around 8th magnitude and it could do a little better this time.  The comet could be visible from the UK from the beginning of the year until August.  It begins the year retrograding in Orion, then swings northward and through Taurus, Gemini, Cancer, Leo and Virgo.  It should be at its best in June, when it is in Leo, but could be a binocular object from April.

 

45P/Honda-Mrkos-Pajdusakova makes its 11th observed return since discovery in 1948 (it was missed in 1959).  It has had several close encounters with Jupiter, the most recent in 1983 which made dramatic changes to w and W.  The perihelion distance has steadily decreased and is now the smallest it has been for the last 200 years.  It can approach quite closely to the Earth and will do so in 2011 (0.06 AU) and 2017 (0.09 AU).  At present the MPC only lists eight approaches closer than 0.06 AU out of 20 passes closer than 0.102 AU, and five of these are by periodic comets.  It can also pass close to Venus and does so on June 4th, when it passes at 0.083 AU.  It was well observed in 1995/96, when it reached 7th magnitude, but in 2001 it was fading from 9th magnitude.  This is not a favourable return for UK observers, but it may be seen from further south during May and June when it is a morning object on its way in to perihelion.

 

52P/Harrington-Abell was discovered on a plate taken for the Palomar Sky Survey by Robert G Harrington and George O Abell.  This is the eighth observed return of the comet since its discovery in 1955 and it never became brighter than 17th magnitude until 1998.  It was not expected to get brighter than 15th magnitude at that return, however it was found in outburst at 12th magnitude in 1998 July, which was seven magnitudes brighter than expected.  After the outburst it faded, and it is unclear how bright it will get this time around.  In any case, it is not a favourable return and is poorly placed for observation from the UK.

 

71P/Clark Michael Clark of Mount John Observatory, New Zealand discovered this comet on a variable star patrol plate in June 1973.  At discovery the magnitude reached 13, but alternate returns are unfavourable and it is then 5 magnitudes fainter, though it hasn’t been missed.  An encounter with Jupiter in 1954 put it into its present orbit, which is such that it can approach quite closely to Mars, passing within 0.09 AU in 1978.  This is the comet’s 7th return since discovery and it could reach 10th magnitude.  As might be expected from the discovery, it is best seen from the Southern Hemisphere and will not be visible from the UK.

 

Professor Arnold Schwassmann and Artur A Wachmann of Hamburg Observatory discovered their third periodic comet on minor planet patrol plates taken on 1930 May 2.  Initially of magnitude 9.5 it brightened to nearly 6m, thanks to a very close approach to Earth (0.062 AU) on June 1.  The initial orbit was a little uncertain and the comet wasn’t found at the next or succeeding apparitions until 1979.  The comet passed within 0.9 AU of Jupiter in 1953, and 0.25 AU in 1965.  In August 1979, Michael Candy reported the discovery of a comet on a plate taken by J Johnston and M Buhagiar while searching for minor planets; this had the motion expected for 73P/Schwassmann-Wachmann, but with perihelion 34 days later than in a prediction by Brian Marsden.  Missed again at the next return, it has been seen at the last three returns.  At the 1995 return the comet underwent a major outburst near perihelion, reaching 5m when it was only expected to be 12m.  Subsequently four components were observed, though calculations by Sekanina suggested that the fragmentation occurred after the outburst.  Three fragments were recovered in 2001, but only a few visual observations were reported as the comet was poorly placed and the absolute magnitude had clearly faded a little from the previous return.  The components have now separated in the date of perihelion by roughly a day. 

 

The comet's 1930 approach to Earth is currently ninth on the list of well-determined cometary approaches to our planet.  In May the fragments will make another close approach, when the brightest one could again reach 7m or brighter, possibly even becoming visible to the naked eye.  The encounter circumstances are favourable for the UK.  At closest approach the fragments will be racing across the sky at around 4.5° a day, though they are separated by around ten degrees from each other.  Their exact paths across the sky will only be determined after recovery due to uncertainties in the non-gravitational parameters for each fragment and the extremely close approach.  The main fragment (C) is currently predicted to pass at 0.073 AU on May 13.22 when it is in Vulpecula.  The other fragments (B and E) will follow it, approach closer and be further north in the sky (May 14.60, 0.065 AU; May 17.32, 0.052 AU); the pass of fragment E will replace the 1930 pass as the 9th closest cometary encounter and the other two will be 12th and 14th closest.  After the encounter they rapidly head south and will be difficult to observe a week later. 

 

With the orbit approaching so closely to the Earth, an associated meteor shower might be expected, and the comet has been linked to the Tau Herculid shower, though the radiant now lies in the Bootes - Serpens region.  Strong activity was reported in 1930 by a lone Japanese observer, but little has been seen since then.  It is likely that any future activity would be in the form of a short-lived outburst, confined to years when the comet is at perihelion. 

 

There are several close cometary approaches in the 2nd decade of the 21st century.  Three feature comets at perihelion this year, with 41P/ approaching to 0.135 AU in 2017, in addition to the approaches of 45P/ already mentioned.  There are five others, with 2000 G1 passing at only 0.032 AU in 2016 (4th closest) and 2004 CB passing at 0.051 AU in 2014 (9th closest).  The brightest pass is that of 46P/Wirtanen, which may be a circumpolar object of 3rd magnitude over Christmas 2018, when it passes 0.076 AU at mid month.

 

76P/West-Kohoutek-Ikemura was discovered in 1975 following a very close encounter with Jupiter in 1972 which produced one of the largest reductions of perihelion distance on record, reducing q from 5.0 to 1.4 AU.  Lubos Kohoutek was actually taking a confirmation plate for a second comet (75P/Kohoutek) discovered 18 days earlier and then lost.  Although 12m at the discovery apparition, it is another comet that has not done so well on subsequent returns and it may not trouble visual observers this time round.

 

80P/Peters-Hartley.  This will be the fifth observed return of the comet, which was discovered in 1846, then lost until it was accidentally recovered in 1982.  At its first apparition the comet was quite bright, 8-9m, which suggests that its absolute magnitude may have faded over the past 150 years.  No visual observations were reported at the last return when it was expected to reach 13th magnitude, though it was observed in 1990.

 

102P/Shoemaker.  The comet was discovered at the very favourable return in 1984, following a close approach to Jupiter in 1980 which reduced the perihelion distance from 3.8 to 2.0 AU.  In 1984 it reached 11m however no further visual observations have been reported to the Section.  This apparition is a little better than the last one, but it will probably not be until the next apparition, which is similar to that of the discovery, that we will visually observe it again.

 

1991 V1 (P/Shoemaker-Levy) was discovered by the Shoemaker-Levy team with the Palomar Schmidt on 1991 November 7 at photographic magnitude 13.  Prior to discovery it was at high southern declinations and could potentially have been discovered by amateur comet seekers.  It wasn’t seen last time round, but the circumstances this time are similar to that of discovery.  It will initially be a Southern Hemisphere object, but moves north after perihelion, so that UK observers may pick it up in late November.  It could be 11th magnitude, but many one-apparition comets disappoint the next time they are recovered.

 

Comet 2005 E2 (McNaught) was discovered by BAA Member Rob McNaught on March 12.75 with the 0.5m Uppsala Schmidt, during the course of the Siding Spring Survey. It reaches perihelion at 1.52 AU in late February 2006, when it could reach 9th magnitude. It should become visible to UK observers in December and will remain visible at 9 - 10 magnitude until April, when it enters solar conjunction.  Next best of recently discovered objects is comet 2004 B1 (LINEAR), which may get to 13th magnitude.  Sebastian Hoenig has predicted that 2002 R5 (SOHO) may return in August.  If his prediction holds, the object could become visible to Southern Hemisphere observers prior to perihelion, but is unlikely to be brighter than 12th magnitude.

 

Several other periodic and parabolic comets are at perihelion during 2006, however they are unlikely to become brighter than 13th magnitude or are poorly placed.  Ephemerides for these can be found on the CBAT WWW pages.  3D/Biela, and 5D/Brorsen have not been seen since the 19th century, whilst D/Skiff-Kosai and D/Lovas were only seen once, and for all four the likely perihelion dates and magnitudes are extremely uncertain.

 

Looking ahead to 2007, the two brightest comets are 2P/Encke and 96P/Machholz and there may be more than two dozen fainter ones.  2P/Encke puts on a brief showing in the evening sky just before perihelion, when it may be a binocular object.  After perihelion it may be visible in the SOHO LASCO field or that of its successor.  96P/Machholz is also best seen in the coronagraph field, when it reaches 2nd magnitude.  UK observers may pick it up after perihelion, but it will be a fading telescopic object.  8P/Tuttle is really a comet for 2008, however it could be a binocular or even naked eye object at the close of 2007 as it makes a close pass of the Earth at 0.25 AU at the beginning of the New Year.

 

Comets reaching perihelion in 2006

 

Comet

   T

 q

  P

 N

 H1

  K1

Peak mag

3D/Biela

 Jan 23

 0.8

 6.7

6

 8.1?

 10.0

?

 

170P/Christensen (2005 M1)

 Jan 26.8

 2.93

 8.63

1

12.0

 10.0

18

 

LINEAR (2002 VQ94)

 Feb  6.7

 6.80

3000

0

9.5

  5.0

18

 

LINEAR (2004 B1)

 Feb  7.9

 1.60

 

0

10.5

  5.0

13

 

NEAT (2004 D1)

 Feb 10.8

 4.97

 

0

11.5

  5.0

18

 

132P/Helin-Roman-Alu

 Feb 15.0

 1.92

 8.28

2

10.1

 10.0

15

 

P/Catalina (2005 JY126)

 Feb 21.3

 2.13

 7.27

0

11.5

 10.0

17

 

McNaught (2005 E2)

 Feb 23.5

 1.52

 

0

 5.5

 10.0

9

 

Christensen (2005 B1)

 Feb 23.6

 3.20

 

0

 6.5

 10.0

14

 

LINEAR (2005 G1)

 Feb 27.3

 4.96

 

0

 8.0

 10.0

18

 

98P/Takamizawa

 Mar  6.5

 1.66

 7.40

3

11.5

 15.0

16

 

83P/Russell

 Apr  7.7

 2.17

 7.62

2

12.0

 10.0

16

 

LINEAR (2003 WT42)

 Apr 10.8

 5.19

 

0

 9.2

  5.0

16

 

P/LONEOS (1999 RO28)

 May 11.8

 1.23

 6.61

1

18.0

  5.0

20

 

71P/Clark

 June  7.2

 1.56

 5.52

6

 8.6

 15.0

10

 

102P/Shoemaker

 June  7.3

 1.97

 7.23

3

 8.0

 15.0

14

 

73P/Schwassmann-Wachmann (C)

 June  7.4

 0.94

 5.36

5

 5.5?

  7.0

?

 

73P/Schwassmann-Wachmann (B)

 June  8.2

 0.94

 5.36

1

 5.5?

  7.0

?

 

73P/Schwassmann-Wachmann (E)

 June 9.6

 0.94

 5.36

1

 5.5?

  7.0

?

 

41P/Tuttle-Giacobini-Kresak

 June 11.3

 1.05

 5.42

9

 7.0

 15.0

7

 

45P/Honda-Mrkos-Pajdusakova

 June 29.8

 0.53

 5.25

10

11.0

 11.1

9

 

5D/Brorsen

 July 6

 0.6

 5.7

5

 9.3?

 10.0

?

 

P/Hug-Bell (1999 X1)

 July  6.7

 1.95

 7.06

1

13.5

 10.0

18

 

84P/Giclas

 Aug  7.5

 1.85

 6.97

5

 9.5

 20.0

16

 

SOHO

 Aug 8

 0.05

 3.93

1

14?

  5.0

7 ?

 

52P/Harrington-Abell

 Aug 14.8

 1.76

 7.54

7

 6.8

 15.0

13

 

D/Skiff-Kosai (1977 C1)

 Aug 31

 2.80

 7.47

1

 8.5

 15.0

?

 

114P/Wiseman-Skiff

 Sep 13.2

 1.58

 6.68

3

11.5

 15.0

16

 

80P/Peters-Hartley

 Sep 25.8

 1.63

 8.14

4

 8.5

 15.0

13

 

112P/Urata-Niijima

 Oct 29.6

 1.46

 6.67

3

14.0

 15.0

15

 

P/Hergenrother (2000 C1)

 Nov  6.9

 2.09

 6.62

1

14.0

 10.0

19

 

D/Lovas (1986 W1)

 Nov 23

 1.40

 6.61

1

10.0

 10.0

?

 

4P/Faye

 Nov 15.5

 1.67

 7.55

19

 6.0

 20.4

10

 

P/Shoemaker-Levy (1991 V1)

 Nov 17.0

 1.13

 7.53

1

10.5

 10.0

11

 

76P/West-Kohoutek-Ikemura

 Nov 19.6

 1.60

 6.48

4

 8.0

 30.0

14

 

P/LINEAR (2000 R2)

 Dec 15.1

 1.46

 6.13

1

18.0

 10.0

21

 

 

The date of perihelion (T), perihelion distance (q), period (P), the number of previously observed returns (N), the magnitude parameters H1 and K1 and the brightest magnitude are given for each comet.  The date of return of 3D/Biela and 5D/Brorsen must be regarded as highly uncertain, whilst both D/Skiff-Kosai and D/Lovas have only been seen once and missed at several returns.

 

Note: m1 = H1 + 5.0 * log(d) + K1 * log(r)

 

References and sources

 

Belyaev, N. A., Kresak, L., Pittich, E. M. and Pushkarev, A. N., Catalogue of short Period Comets, Bratislava (1986).

Hoenig, S. F.,  Identification of a new short-period comet near the Sun, A&A (in press).

Kozlov, E. A., Medvedev, Y. D., Pittichova, J., and Pittich, E. M. Catalogue of short Period Comets, 2nd edition, (http://astro.savba.sk/cat/) (2003).

Kronk, G. W., Cometographia, Cambridge University Press, (1999, 2004) and http://www.cometography.com.

Marsden, B. G.  Catalogue of Cometary Orbits, 15th edition, IAU CBAT, (2003).

Nakano Notes at http://www.oaa.gr.jp/~oaacs/nk/

Nakano, S. and Green D. W. E., Eds, International Comet Quarterly 2005 Comet Handbook, (2004).

Shanklin, J. D.,  Observing Guide to Comets, 2nd edition (2002)

 

Jonathan Shanklin