Comet Hale-Bopp (1995 O1), the great comet of 1997, is fading slowly and could still be 11m at the beginning of the year, fading to 13m by the year's end. It is only observable from Southern Hemisphere locations as it loops round the Large Magellanic Cloud.
Comet LINEAR (1998 M5) is at perihelion in January at around 10th magnitude and moves north from Lyra, passing very close to the pole in mid March. Heading south it passes through Camelopardalus and Lynx, reaching Cancer mid year when it will have faded to 13th magnitude. It will then be too faint and close to the sun for further observation.
21P/Giacobini-Zinner will still be visible at the beginning of the year in Cetus and Eridanus as it fades from 10th magnitude. It fades quite rapidly and will be lost by the end of February. It is not well placed for observation from the UK, but will be visible from further south.
29P/Schwassmann-Wachmann 1 is an annual comet which has frequent outbursts and seems to be more often active than not at the moment, though it rarely gets brighter than 12m. In the first half of 1998 it was in outburst on several occasions. The randomly spaced outbursts may be due to a thermal heat wave propagating into the nucleus and triggering sublimation of CO inside the comet. This year it is at opposition in May on the borders of Hydra and Libra. It is in solar conjunction in November, passing into Scorpius. This comet is an ideal target for those equipped with CCDs and it should be observed at every opportunity. Unfortunately opportunities for UK observers may be limited as its altitude does not exceed 15? from this country.
10P/Tempel 2 makes its 20th observed return since its discovery by William Tempel (Milan, Italy) as a 9th magnitude object in 1873. Several unfavourable returns were missed in the earlier years. The orbit is very stable, which is one reason why it is a favoured target for planned spacecraft missions. In 1983 the IRAS satellite detected an extensive dust trail behind the comet. Normally the light curve is highly asymmetric with a late turn on. There is a rapid rise in brightness as perihelion approaches, which continues more slowly for a couple more weeks after perihelion, followed by a slow decline until activity switches off. With a 5.5 year period alternate returns are favourable and this is one of them. The comet may be picked up in large telescopes in April when it is in Ophiuchus and it should reach 10th magnitude in June. It is closest to the Earth in July (0.65 AU) when it could be 9th magnitude and UK observers should be able to follow it until August, but it then moves too far south. More southerly observers may be able to observe it until the end of the year as it fades.
Donald Machholz discovered P/Machholz 2 (1994 P1) with his 0.25-m reflector at 10m in August 1994. It proved to have multiple components, first reported by Michael Jager (Vienna, Austria). The four secondary components could all be described by the same orbit, but with perihelion delayed by up to half a day from the primary. At times there seemed to be a faint trail of material linking the components. The comet has a short period of 5.2 years with a perihelion distance of 0.75 AU and aphelion just inside the orbit of Jupiter. The orbit has been slowly evolving, with progressive changes occurring about every 50 years, thanks to approaches to Jupiter. The most recent close approach was in 1982. With a relatively stable perihelion distance, which is slowly increasing, it is perhaps surprising that the comet was not discovered earlier. There was a favourable return in autumn 1978 when it might have reached 8th magnitude and very favourable returns in the autumns of 1920, 1937 and 1957 when it might have reached 6th magnitude. The fact that it was not discovered at any of these returns suggests either that the orbital evolution is slightly inaccurate, or that the absolute magnitude at the 1994 return was not typical. At present the earth passes about 0.25 AU outside the descending node and the orbital evolution will slowly decrease this distance, raising the possibility of meteor shower from the comet in a few hundred years time.
This return is moderately favourable with the comet moving rapidly eastwards through Serpens (October), Scutum and Aquila (November), Aquarius and Capricornus (December) as it brightens from 14th to 7th magnitude. The date of perihelion is uncertain by up to a day and more accurate ephemerides will be available when the comet is recovered. UK observers should be able to observe it from November at 10th magnitude, though more southerly observers may find it a month earlier.
52P/Harrington-Abell reaches perihelion and opposition in late January. This is the seventh observed return of the comet since its discovery in 1954 and it has never became brighter than 17th magnitude at previous returns. Normally it would not be expected to get brighter than 15th magnitude at this return, however it was found in outburst at 12th magnitude in July 1998 and was 7 magnitudes brighter than expected. It will be well placed for UK observation, and if the outburst continues it could be visible in binoculars.
A number of fainter comets may be of interest to CCD observers. These include: Meunier-Dupouy (1997 J2) (fading from 13m in January), 37P/Forbes (13m between April and June), 88P/Howell (fading from 13m in January), 93P/Lovas 1 (fading from 13m in January), 95P/Chiron (16m at opposition in late May in Libra) and 114P/Wiseman-Skiff (brightening from 14m in November). Ephemerides for these can be found on the CBAT WWW pages. CCD V magnitudes of Chiron would be of particular interest as observations show that its absolute magnitude varies erratically.
Several other comets return to perihelion during 1999, however they are unlikely to become bright enough to observe or are poorly placed. 4P/Faye, 9P/Tempel 1, 50P/Arend, 59P/Kearns-Kwee, 63P/Wild 1, 84P/Giclas and 102P/Shoemaker 1 have unfavorable returns. Spacewatch (1997 BA6), 60P/Tsuchinshan 2, 105P/Singer Brewster, 106P/Schuster, 135P/Shoemaker-Levy 8, 136P/Mueller 3, P/Bowell-Skiff, P/Shoemaker-Levy 6, P/Ge-Wang and D/Skiff-Kosai are intrinsically faint or distant comets. D/Schorr and D/Denning have not been seen for many years and are unlikely to be recovered.
Looking ahead, 2000 sees favourable returns of comets 2P/Encke, which may reach 9th magnitude and 73P/Schwassmann- Wachmann 3. The expected magnitude of 73P is uncertain because it outburst at the last return, but it could reach 7th magnitude.
Comets reaching perihelion in 1999
Comet T q P N H1 K1 C/LINEAR (1998 M5) Jan 24.5 1.74 5.5 10 52P/Harrington-Abell Jan 27.9 1.76 7.53 6 13.5 15 60P/Tsuchinshan 2 Mar 08.2 1.77 6.79 5 10.5 15 D/Skiff-Kosai (1977 C1) Mar 09.1 2.79 7.45 1 8.5 15 102P/Shoemaker 1 Mar 15.4 1.98 7.24 2 8.0 15 136P/Mueller 3 Mar 20.5 3.01 8.71 1 11.0 10 D/Schorr (1918 W1) Apr 03.6 2.85 8.5 1 10.0 15 105P/Singer Brewster Apr 06.4 2.03 6.44 2 12.5 15 P/Bowell-Skiff Apr 27.6 1.97 16.1 1 11.5 15 P/Shoemaker-Levy 6 May 02.4 1.13 7.55 1 10.5 10 37P/Forbes May 04.2 1.45 6.13 8 10.5 10 4P/Faye May 06.1 1.66 7.52 19 6.0 20 P/Ge-Wang Jun 26.9 2.50 11.2 1 11.0 10 50P/Arend Aug 03.8 1.92 8.24 6 9.5 15 84P/Giclas Aug 25.1 1.85 6.96 4 8.7 15 10P/Tempel 2 Sep 08.4 1.48 5.47 19 5.0 25 59P/Kerns-Kwee Sep 16.3 2.34 9.45 4 7.5 15 D/Denning (1894 F1) Nov 20.3 1.08 7.2 1 10.5 15 C/Spacewatch (1997 BA6) Nov 27.7 3.44 5.0 10 P/Machholz 2 Dec 07.5 0.75 5.21 1 12.5 30 135P/Shoemaker-Levy 8 Dec 10.6 2.72 7.49 1 6.5 20 106P/Schuster Dec 16.2 1.55 7.29 2 10.0 15 63P/Wild 1 Dec 27.4 1.96 13.2 2 10.5 15The 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
1. Taylor, G. E., The Handbook of the British Astronomical
Association for 1999, (1998).
2.
http://www.info.waseda.ac.jp/muraoka/members/seiichi/index.ht
ml
3. Nakano, S. and Green D. W. E., Eds, International Comet
Quarterly 1999 Comet Handbook, (1998).
4. Shanklin, J. D., Observing Guide to Comets, (1996).
5. Marsden, B. G. Catalogue of Cometary Orbits, 12th
edition, IAU CBAT, (1998).
6. Kronk, G. W., Comets A Descriptive Catalogue, Enslow,
(1984).
7. Ridley, H. B., Prospects for Comets (Annual series).
Jonathan Shanklin