Comet Prospects for 2005

2005 sees the possible return of 27 periodic comets. None are particularly bright, but several are like to come within range of visual observation with moderate apertures. Three long period comets are likely to be easily visible in binoculars. 2003 K4 (LINEAR) may be fading from 6^th magnitude after its perihelion in October 2004, though at the time of writing there are hints that it may be coming to a premature end. 2003 T4 (LINEAR) should reach 6^th magnitude in the spring. 2004 Q2 (Machholz) could be a naked eye object. 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 21^m 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.

9P/Tempel was first observed in 1867, but was lost between 1879 and 1967 following an encounter with Jupiter in 1881, which increased the perihelion distance from 1.8 to 2.1 AU. Further encounters in 1941 and 1953 put q back to 1.5 AU and calculations by Brian Marsden allowed Elizabeth Roemer to recover it in 1967. Alternate returns are favourable, but an encounter with Jupiter in 2024 will once again increase the perihelion distance to 1.8 AU. The 2000 return was an unfavourable one and no observations were reported. It is an important comet to observe, as it is the target for the Deep Impact mission. It may come within visual range as early as 2005 February, when it is visible in the morning sky in Virgo and remains in the constellation until July. It should be at its best in May and June, when it may reach 10^th magnitude in the evening sky, but it heads south as it fades and UK observers will loose it after mid-summer, although elsewhere it should remain visible until October. The impactor of the Deep Impact spacecraft is expected to hit the comet on July 4^th with a variety of possible outcomes. Observers who want to witness the event should head south of around 50°N because the object will be rather too low from the UK unless there is a spectacular outburst.

21P/Giacobini-Zinner is the parent comet of the October Draconid meteors. On this occasion we pass just inside the comet’s orbit 92 days after the comet, with any shower taking place on October 8.7. The comet was first discovered by Michael Giacobini at Nice observatory in December 1900 and was thought to have a period of 6.8 years. The next two returns were expected to be difficult to observe, but in October 1913, Ernst Zinner, of Bamberg, Germany, discovered a comet whilst observing variable stars in Scutum. This turned out to be the same comet, but the period had been incorrectly determined and was actually 6.5 years. The comet was missed at three unfavourable returns, so the 1998 return was the thirteenth apparition of the comet. This is another mediocre apparition and the closest the comet will get to the Earth is 1.42 AU. It will come within visual range in 2005 March, but is not well placed for the UK until April, when it may be 12^th magnitude. It is a morning object, and draws back into the Sun, so that we will lose it again in May, by which time it may have brightened to 10^th magnitude. For most of this period it is in Pegasus.

29P/Schwassmann-Wachmann 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 12^m. Initially in Pisces, it spends most of the year in Aries, reaching opposition at the end of October. The comet is an ideal target for those equipped with CCDs and it should be observed at every opportunity. It is quite well placed this year and UK based observers should be able to follow it during January and February, when it is in Pisces and throughout the second half of the year when it is in Aries.

37P/Forbes was discovered by A F I Forbes during a visual search with a 20-cm reflector at Hermanus, South Africa on 1929 August 1 at a favourable opposition. It has undergone several encounters with Jupiter, most recently to within 0.38 AU in 1990 and 0.58 AU in 2001. These have pushed out the perihelion distance a little, however this will be the best opposition for the next 50 years. It may come within visual range in 2005 April, but is a southern hemisphere object throughout the apparition, reaching its best (12^th magnitude) in June and July as it passes from Lupus to Scorpius.

62P/Tsuchinshan The comet was discovered at Purple Mountain Observatory, Nanking, China in 1965, following a close approach to Jupiter in 1960, which reduced the perihelion distance from 2 to 1.5 AU. Another encounter in 2020 will reduce it further to 1.3 AU giving an excellent apparition in 2023/24. The inclination is decreasing, combined with a rapid regression of the node and rotation of the orbital plane. Unusually, the comet's name derives from that of the observatory rather than those of the discoverers. At a good apparition such as in 1985 it can reach 11^m and as the perihelion distance will continue to decrease future returns may be even better. At the last return the comet was recorded at around 13^th magnitude and this time it could do a magnitude or more better. It was at perihelion at the end of 2004 and will slowly fade from 11^th magnitude. It will remain visible in the evening sky until April or May as it completes a retrograde loop in Coma.

69P/Taylor A series of Jupiter encounters in the 19^th century reduced the perihelion distance from 3.1 to 1.6 AU and led to its discovery by Clement Taylor, with a 0.25-m reflector from Herschel View, Cape Town South Africa, in November 1915. It was quite bright, 9th magnitude at best, and shortly after perihelion, in 1916 February, E E Barnard found a double nucleus, each with a short tail. The secondary nucleus became brighter than the primary, but then rapidly faded and the primary also faded more rapidly than expected. The comet was then lost until 1977, when new orbital computations led to the recovery of the 'B' component by Charles Kowal with the Palomar Schmidt. The 'A' component was not found. The comet has had several encounters with Jupiter, the closest recent one being in 1925, and had very close (0.06 AU) encounters in 1807 and 1854. The comet was not expected to be brighter than 15^th magnitude at its last return, however it was discovered at around 12.5 in mid January 1998. The observations suggest that it suffered two outbursts. This makes it difficult to predict the likely brightness at this return, and it was recovered in mid October 2004 at 17^th magnitude. Unless it undergoes further outbursts it is unlikely to get within visual range in 2005, however it is worth monitoring the expected position of the comet, particularly by CCD. It retrogrades from Cancer to Lynx then resumes direct motion and reaches the border of Leo Minor and Major by the end of June, when it slips into the twilight.

78P/Gehrels Tom Gehrels discovered this comet at Palomar in 1973. Its perihelion distance is slowly decreasing and is currently around the lowest for 200 years. The eccentricity is slowly increasing, with a marked jump in both following a moderately close approach to Jupiter in 1995. This return is extremely favourable, with the comet reaching opposition and perihelion within a fortnight of each other. At the last return the comet reached 12^th magnitude and this time round it had reached 11^th magnitude in mid October. By 2005 it is well past its best, and it will be fading from 11^th magnitude, getting too faint and low in the evening twilight in April. It begins the year in Aries, but spends most of this period in Taurus.

95P/Chiron is an unusual comet in that it is also asteroid 2060. It will reach around 18^m 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 is currently around 6. It began an outburst in 2000/01 though it is likely to be fading again in 2005. 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 40 year's time.

101P/Chernykh was discovered by Nikolaj Chernykh at the Crimean Astrophysical Observatory whilst scanning routine minor planet survey plates taken on 1977 August 19 and 22. It was a fairly bright object of 14^th magnitude and at its best, at the end of September, it reached 12.5. The succeeding return was a little better, and this one is better again. The comet is an unusual one in playing celestial billiards with both Jupiter and Saturn and has made a number of approaches to both planets, most recently passing 0.35 AU from Jupiter in 1980, which reduced the period to 14 years. It comes into visual range in 2005 May, and reaches its brightest in the autumn, when it may get to 10^th magnitude. It parallels the ecliptic, running from Aquarius into Pisces and remains visible into 2006.

121P/Shoemaker-Holt was discovered by Carolyn and Eugene Shoemaker and Henry Holt with the Palomar 0.46-m Schmidt on 1989 March 9 and at its brightest reached around 13^th magnitude. It made a moderately close approach to Jupiter in 1984 and does not approach closer to the Earth than 1.7 AU. With a period of just over 8 years, circumstances do not change much from apparition to apparition so a similar performance is expected for the 2004 – 2005 apparition. It should remain within visual range for the first three months of the year as it retrogrades in Leo Minor.

P/1983 V1 (Hartley-IRAS) John Davies and Simon Green of Leicester University reported the discovery of a fast moving object by IRAS (the Infra-Red Astronomy Satellite) on 1983 November 11. On being asked to confirm the object, Ken Russell of the UK Schmidt Telescope Unit reported that Malcolm Hartley had discovered a comet on a plate taken 6 days earlier, that was probably the same object, but due to moonlight it wasn’t captured on a confirming plate until November 23. The comet has a retrograde orbit (just) with a period of 21.5 years, and 2005 is its first return since discovery. It reached 10^th magnitude in 1984 January and should attain a similar magnitude this time round. It emerges sufficiently far from the Sun for observation from the UK in 2005 June, by which time it is nearing its brightest. Moving north from Andromeda, it rapidly becomes circumpolar, passing some 9° from the pole in July. It slowly fades and we should be able to follow it until September, by which time it has crossed into Canes Venatici. On its way out from perihelion at its next return it will pass fairly close to Jupiter in 2028, an encounter that will reduce the perihelion distance to 1.22 AU.

Three long period comets are likely to be binocular objects or better, and there are several fainter objects that should be within view during 2005. C/2001 Q4 (NEAT) was discovered at Palomar on 2001 August 24.40 when it was nearly three years from perihelion and over 10 AU from the Sun. It was a bright object in May 2004, but will be fading from 12^th magnitude during the first quarter of the year. C/2002 T7 (LINEAR) was also a bright object in May 2004 and will be fading from 12^th magnitude at the beginning of the year. It doesn’t become visible from the UK again until 2005 March, by which time it will probably be too faint for visual observation. C/2003 T3 (Tabur) will soon fade from 13^th magnitude, but may still be visible in Ursa Major at the beginning of the year. C/2004 L1 (LINEAR) may get to 13^th magnitude.

Two of the brighter comets of the year were both discovered by LINEAR. C/2003 K4 (LINEAR) could be fading from 6^th magnitude at the beginning of the year and will remain in view until the summer, at least for southern hemisphere observers. It was however, not as bright as expected as it passed through the SOHO LASCO C3 field, and its activity may be on the wane. C/2003 T4 (LINEAR) brightens from 10^th magnitude at the beginning of the year and is at its brightest, around 6^th magnitude, in March and April. Starting the year in Lyra, it rapidly heads south and will be observable from the Southern Hemisphere until the autumn. UK observers will be able to see it in the evening sky in January and in the morning sky until the end of March. The brightest expected comet for the year is C/2004 Q2 (Machholz). This is excellently placed for observation in the January evening sky, when it could be 3^rd magnitude. Starting the year in Taurus it rapidly moves north, passing some 5° from the pole in March. It remains well placed, and could be a binocular object until May, by which time it has reached Ursa Major.

Several other periodic comets are at perihelion during 2005, however they are unlikely to become brighter than 13^th magnitude or are poorly placed. 32P/Comas Sola, 49P/Arend-Rigaux and 60P/Tsuchinshan do not get brighter than 13^th magnitude. 10P/Tempel, 141P/Machholz, P/1998 W1 (Spahr) and P/1998 X1 (ODAS) have unfavourable returns. 56P/Slaughter-Burnham, 72P/Denning-Fujikawa, 91P/Russell, 105P/Singer Brewster, 107P/Wilson-Harrington, 117P/Helin-Roman-Alu, 119P/Parker-Hartley, 129P/Shoemaker-Levy, 138P/Shoemaker-Levy, P/1998 W2 (Hergenrother) and P/2000 G1 (LINEAR) are intrinsically faint or distant comets and will not come within visual range. Ephemerides for these can be found on the CBAT WWW pages. 3D/Biela, D/1884 O1, D/1886 K1 and D/1892 T1 have not been seen since the 19^th century and their likely perihelion dates and magnitudes are extremely uncertain.

Looking ahead to 2006, the main component of 73P/Schwassmann-Wachmann will pass 0.08 AU from the Earth, with closest approach on May 12 at 19:52. Exactly how bright it will get is anybody’s guess as it fragmented in 1995, but it could be visible to the naked eye. Other fragments pass from May 13 to 17 at distances between 0.052 to 0.074 AU. Although 45P/Honda-Mrkos-Pajdusakova may reach 9^th magnitude, it won’t be seen as it is too close to the Sun. At its next return in 2011 it will pass 0.06 AU from the Earth. Next best in 2006 is 4P/Faye, which may reach 10^th magnitude in the autumn.

Comets reaching perihelion in 2005

Comet	T		q	P		N		H1		K1	Peak mag
2004 F3 (P/NEAT)	Jan 4.3	4.31			8.04		0		9.0	10.0	15
56P/Slaughter-Burnham	Jan 15.0	2.54			11.55		4		8.0	15.0	16
2004 Q2 (Machholz)	Jan 24.9	1.21							6.1	7.5	4
3D/Biela	Feb 1.5	0.80			6.54		6		8.0	15.0	?
10P/Tempel	Feb 15.0	1.43			5.38		20		9.0	12.5	13
49P/Arend-Rigaux	Feb 24.6	1.37			6.61		8		11.3	11.0	14
141P/Machholz (A)	Feb 27.8	0.75			5.23		2		13.4	29.8	11 ?
141P/Machholz (D)	Mar 2.5	0.75			5.23		2		13.4	29.8	11 ?
2004 L1 (LINEAR)	Mar 30.1	2.05							10.0	10.0	13
32P/Comas Sola	Apr 1.3	1.83			8.78		9		6.5	20.0	13
2003 T4 (LINEAR)	Apr 3.6	0.85							6.0	10.0	6
1998 X1 (P/ODAS)	May 2.5	1.98			6.78		1		10.5	15.0	17
1892 T1 (D/Barnard)	May 3.2	1.56			7.02		1		8.0	15.0	?
119P/Parker-Hartley	May 24.3	3.04			8.89		2		9.0	8.0	15
1886 K1 (D/Brooks)	May 30.8	1.88			6.67		1		8.0	15.0	?
129P/Shoemaker-Levy	Jun 4.7	2.81			7.23		2		11.0	10.0	17
72P/Denning-Fujikawa	Jun 20.0	0.80			9.08		2		15.5	25.0	14
1983 V1 (P/Hartley-IRAS)	Jun 26.8	1.28			21.52		1		8.0	10.0	10
91P/Russell	Jun 26.8	2.60			7.67		3		7.5	15.0	15
21P/Giacobini-Zinner	Jul 2.8	1.04			6.62		13		8.5	10.6	10
2004 K1 (Catalina)	Jul 5.2	3.40							7.0	10.0	14
9P/Tempel	Jul 5.3	1.51			5.52		10		5.4	25.0	10
2000 G1 (P/LINEAR)	Jul 13.9	1.00			5.34		1		19.5	5.0	21
138P/Shoemaker-Levy	Jul 19.9	1.71			6.91		2		15.0	10.0	19
107P/Wilson-Harrington	Jul 10.7	0.99			4.29		6		15.0	5.0	15
37P/Forbes	Aug 1.7	1.57			6.35		9		10.5	10.0	12
1998 W1 (P/Spahr)	Sep 3.4	1.73			6.62		1		10.2	15.0	15
105P/Singer Brewster	Sep 11.3	2.04			6.45		3		12.5	15.0	19
1884 O1 (D/Barnard)	Sep 20.8	1.33			5.46		1		11.5	15.0	?
1998 W2 (P/Hergenrother)	Nov 2.2	1.43			6.92		1		14.5	10.0	15
2004 L2 (LINEAR)	Nov 15.0	3.78							10.0	10.0	18
117P/Helin-Roman-Alu	Dec 19.9	3.04			8.24		2		2.5	20.0	14
60P/Tsuchinshan	Dec 24.1	1.77			6.78		6		10.5	15.0	14
101P/Chernykh	Dec 25.0	2.35			13.92		2		3.3	15.0	10

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 brightest magnitude given for 29P is that typical of an outburst. Comet 141P/Machholz has experienced a number of fragmentations and the magnitude of the components is uncertain.

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

References and sources

Nakano, S. and Green D. W. E., Eds, International Comet Quarterly 2004 Comet Handbook, (2003).

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

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

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).

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

Jonathan Shanklin