Comet Prospects for 2003

 

2003 sees the return of 16 periodic comets. The brightest of the year is predicted to be 2P/Encke, which is making its 59th predicted return at the end of the year and may reach 6th magnitude. 2001 Q4 (NEAT) reaches perihelion in 2004 and may reach binocular visibility at the end of the year. Several other long-period comets discovered in previous years are still visible. 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 18m are given in the International Comet Quarterly Handbook; details of subscription to the ICQ are available from the comet section Director. The section booklet on comet observing is available from the BAA office or the Director.

 

This year sees comet 2P/Encke's 59th observed return to perihelion since its discovery by Mechain in 1786. The orbit is quite stable, and with a period of 3.3 years apparitions repeat on a 10-year cycle. This year the comet is well seen from the Northern Hemisphere prior to perihelion, which is in late December. The comet tracks through Andromeda during October and early November, then accelerates southwards through Cygnus and begins December in Ophiuchus. The comet might be observable from October until early December, when it could be 6th magnitude. This magnitude may however be optimistic as observations from the SOHO spacecraft in 2000 showed that it suddenly brightened after perihelion, by which time it will be at a poor elongation. A possible explanation of this behaviour is that Encke has two active regions, an old one with declining activity, which operates prior to perihelion and a recently activated one present after perihelion. There is, however, little evidence for a secular fading in the archive of BAA observations of the comet. The comet is the progenitor of the Taurid meteor complex and may be associated with several Apollo asteroids.

 

22P/Kopff reached perihelion at the end of 2002 and although it is near its brightest, the solar elongation is poor and it is unlikely to be seen this year.

 

29P/Schwassmann-Wachmann 1 is an annual comet that has frequent outbursts and seems to be more often active than not at the moment, though it rarely gets brighter than 12m. It begins the year in Capricornus, but spends most of the year in Aquarius, reaching opposition at the beginning of September. The comet is an ideal target for those equipped with CCDs and it should be observed at every opportunity. UK based observers should be able to follow it throughout the second half of the year.

 

30P/Reinmuth 1 was at perihelion last year, and is a little brighter at the start of this year, although only 14th magnitude. Best seen in the morning sky, it reaches opposition in March, but by then is fading quite rapidly. The comet was discovered during the course of a regular photographic asteroid survey by Karl Reinmuth at Heidelberg Observatory on a photograph exposed on 1928 February 22.96. If the comet gets as bright as predicted this could be the best return since the comet's discovery.

 

43P/Wolf-Harrington does not reach perihelion until 2004, but it gets to 14th magnitude in September and should be 13th magnitude at the end of the year. It is favourably placed in the evening sky and CCD observers should certainly have a go at following the comet. This will be its tenth observed return, which was discovered in 1924, then lost until 1951. The comet is in a chaotic orbit, and made a close approach to Jupiter in 1936 which reduced its perihelion distance from 2.4 to 1.6 AU. It made an exceptionally close (0.003 AU) approach to Jupiter in 1841, which switched its previous perihelion distance into the new aphelion distance.

 

53P/van Biesbroeck is an interesting object. George van Biesbroeck discovered it at Yerkes observatory in September 1954. Stan Milbourn and George Lea calculated the best recovery orbit and the comet was duly recovered in May 1965. Back calculating the orbit shows that it made a moderately close approach to Jupiter in 1850, which reduced q from 2.7 to 2.4 AU and reversed the nodes. The pre 1850 orbit is very similar to that of 42P/Neujmin 3 and it is likely that they are fragments of the same parent. The comet has a relatively favourable return and just reaches 14th magnitude, however it lies south of the equator and will be difficult to observe from the UK.

 

65P/Gunn was discovered in 1970 after a perturbation by Jupiter in 1965 had reduced the perihelion distance from 3.39 to 2.44 AU. In 1980 two pre-discovery images were found on Palomar plates taken in 1954. The comet can be followed all round the orbit as it has a relatively low eccentricity of 0.32. At the last return in 1996 it reached 13th magnitude and it will do a little better this time, as it is at opposition when at perihelion. It will be at moderate southern declination throughout the apparition and is essentially unobservable from the UK.

 

66P/du Toit has only been observed at alternate returns and its last return in 1988 was about the worst possible. It was discovered by Daniel du Toit at the Boyden Observatory in South Africa on 1944 May 16. The discovery return was a good one, with the comet approaching to within 0.5 AU of the Earth, and the comet reached 10th magnitude. It was not found at the 1959 return, nor was it initially found in 1974, however in January 1975 a further inspection of search plates taken ten months previously revealed a diffuse image of the comet. This return is moderately favourable, and the comet could reach 13th magnitude, however, as at the discovery return, it will essentially be a Southern Hemisphere object.

 

81P/Wild 2 is a new comet that made a very close (0.006 AU) approach to Jupiter in September 1974. Prior to this it was in a 40-year orbit that had perihelion at 5 AU and aphelion at 25 AU. The comet was discovered by Paul Wild with the 40/60-cm Schmidt at Zimmerwald on 1978 January 6. The Stardust spacecraft is due to visit the comet in 2004 and recover material for return to earth in 2006. The comet reaches perihelion in September, but unfortunately the elongation is very poor and the comet will be difficult to observe at this return.

 

95P/Chiron is an unusual comet in that it is also asteroid 2060. It reaches 17m when at opposition in July in Sagittarius. CCD V magnitudes of Chiron would be of particular interest as observations show that its absolute magnitude varies erratically. It was at perihelion in 1996 when it was 8.5 AU from the Sun and will be nearly 19 AU from the Sun at aphelion in around 50 years time.

 

116P/Wild 4 was discovered on 1990 January 21.98 by Paul Wild with the 0.40-m Schmidt at the Zimmerwald station of the Berne Astronomical Institute at a photographic magnitude of 13.5. At its brightest the comet only reached 12m, but it was surprisingly well observed. The comet was perturbed into its present orbit after a close approach to Jupiter in mid 1987. The comet is at perihelion in January, but is poorly placed for viewing from the UK. It brightens from 13th magnitude at the beginning of the year to 12th magnitude in April as it nears opposition but is a long way south. It remains brighter than 13th magnitude until July.

 

123P/West-Hartley was discovered by Richard West on an ESO survey plate taken on March 14 and independently by Malcolm Hartley on a UK Schmidt plate taken on May 28. The comet has made no recent close approaches to Jupiter. It reached between 13th and 14th magnitude at the last return in 1996. It should achieve a similar brightness this time round, but is at its brightest early in the New Year after its December perihelion.

 

P/Shoemaker 3 (1986 A1) reached perihelion last year, and is making its first return since discovery. It will be quite faint, around 14-13th magnitude when it is at opposition in February. It moves northwards in the sickle of Leo.

 

P/Brewington 2 (1992 Q1) makes its first return since its discovery in 1992. It was discovered by Howard J Brewington of Cloudcroft, New Mexico, as a small diffuse 10m object on August 28.41 using a 0.40-m reflector x55. This was his fourth discovery and his second periodic one. The comet is in a Jupiter crossing orbit, but has not approached the planet for several revolutions. At a favourable return it could reach 7m, but this return is not particularly favourable. It is an evening object, of around 10 - 11th magnitude, but its solar elongation decreases from 50 at the beginning of the year and we will loose it in the March twilight.

 

Several recently discovered parabolic comets will be visible during 2003. 2001 HT50 (LINEAR) will be a morning object of around 12th magnitude at the start of the year, but it quickly moves towards opposition. It brightens a little, but becomes poorly placed for observation after April. It reaches perihelion whilst in solar conjunction, but re-emerges towards the end of August at around 11th magnitude. The earth continues to approach it until October, when it is fractionally brighter, and it then fades slowly to the end of the year. 2001 Q4 (NEAT) doesn't reach perihelion until 2004, but will be brightening into visual range at the end of 2003. It is however a Southern Hemisphere object and UK observers will have to wait until it heads north in 2004. 2001 RX14 (LINEAR) will be around 10th magnitude at the start of the year. It is a fraction brighter in February, just after perihelion, and only fades slowly, so we will be able to follow it until it sinks into the twilight in June. Initially it is well placed on the borders of Ursa Major and Canes Venatici, then tracks southwards passing through Leo in April and May.

 

Several other comets return to perihelion during 2003, however they are unlikely to become bright enough to observe visually or are poorly placed. 94P/Russell 4, 100P/Hartley 1, 118P/Shoemaker-Levy 4 and 127P/Holt-Olmstead have unfavourable returns whilst 36P/Whipple and 79P/du Toit-Hartley are intrinsically faint or distant comets. Ephemerides for these can be found on the CBAT WWW pages. 25D/Neujmin 2 has not been seen since 1926 and P/Tritton has not been seen since 1978.

 

Looking ahead to 2004, the highlight will almost certainly be 2001 Q4, which may become brighter than 3rd magnitude at perihelion. Several periodic comets have favourable returns, but they will all be telescopic objects.

 

 

Comets reaching perihelion in 2003

 

Comet

T

q

P

N

H1

K1

2001 RX14 (LINEAR)

Jan 18.8

2.06

 

 

6.5

10.0

116P/Wild 4

Jan 21.6

2.17

6.48

2

1.2

25.3

79P/du Toit-Hartley

Feb 15.3

1.23

5.27

3

14.0

15.0

P/Brewington

Feb 18.8

1.59

10.66

1

8.5

13.5

P/Tritton

Mar 6.0

1.43

6.32

1

12.5

10.0

65P/Gunn

May 11.9

2.45

6.80

6

5.0

15.0

25D/Neujmin 2

May 26.4

1.27

5.38

2

10.5

10.0

127P/Holt-Olmstead

Jun 12.5

2.16

6.34

2

14.0

10.0

36P/Whipple

Jul 6.7

3.09

8.51

10

8.5

15.0

2001 HT50 (LINEAR-NEAT)

Jul 8.8

2.80

 

 

4.5

10.0

118P/Shoemaker-Levy 4

Jul 16.8

2.01

6.49

2

8.7

10.0

100P/Hartely 1

Aug 18.0

1.98

6.29

3

8.9

15.0

66P/du Toit

Aug 28.2

1.27

14.70

2

12.0

9.5

94P/Russell 4

Aug 29.2

2.23

6.58

3

9.0

15.0

81P/Wild 2

Sep 25.9

1.59

6.40

4

6.9

11.4

53P/Van Biesbroeck

Oct 9.4

2.42

12.52

4

8.0

15.0

123P/West-Hartley

Dec 9.1

2.13

7.58

2

11.5

10.0

2P/Encke

Dec 29.9

0.34

3.30

58

11.0

15.0

 

The date of perihelion (T), perihelion distance (q), period (P), the number of previously observed returns (N) and the magnitude parameters H1 and K1 are given for each comet.

 

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

 

 

References and sources

 

Nakano, S. and Green D. W. E., Eds, International Comet Quarterly 2002 Comet Handbook, (2001).

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

Marsden, B. G. Catalogue of Cometary Orbits, 14th edition, IAU CBAT, (2001).

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

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

 

Jonathan Shanklin