THE COMET’S TALE
Newsletter of the Comet Section of the British Astronomical Association
Volume 6, No 1 (Issue 11), 1999 April
INTERNATIONAL WORKSHOP ON COMETARY ASTRONOMY
The BAA Comet Section is very at the meeting will lead to some photometry), Charles Morris pleased to be hosting the second conclusions that further improve (possibly on web issues), International Workshop on our observing standards. Mahendra Singh (comet Cometary Astronomy. This will However, observers generally spectroscopy). be held at New Hall Cambridge have very fixed views so expect from August 14 to 16. The some heated arguments! The college bar will be open in the meeting aims to bring together evenings for informal discussion. professional and amateur Although many amateurs observe If it is clear there will be observers and as many comet comets for their own satisfaction, opportunity to use the two historic discoverers as possible. it can add enjoyment if you know refractors at the University that your observations are Observatory. The first IWCA was held at contributing to the scientific Selvino, Italy in February 1994 understanding of comets. To this Cambridge has many sites of and details appeared in the end a number of leading astronomical interest and there Comet's Tale for 1994 May. Four professionals will be at the will be free time for participants to previous American Workshops on meeting, explaining how our explore at their leisure. Many Cometary Astronomy had been observations are used and what famous scientists with comet held in the U.S.A., but had not additional observations would connections studied at Cambridge attracted much attention in help with their research. including Newton, Herschel, Europe. Challis and more recently Bearing all this in mind the Lyttleton. The 1994 meeting marked the 15th meeting has three main goals: 1) anniversary of the ICQ and improving the acquisition of To conclude the meeting I have attracted a good attendance of cometary information. 2) arranged a trip to Stonehenge on active observers. Presentations on increasing understanding as to the Monday evening, when we the work of various national what science can be gained will be allowed in to the inner observing groups were given, through observing comets by both circle to view the stones close up. along with talks by individuals on amateurs and professionals. 3) There have been some suggestions their own particular programs. Of providing a forum in which that Stonehenge was first greater importance were sessions cometary astronomers can meet constructed as either a comet or which focussed on observing others from distant geographical meteor observatory! Numbers for methodologies and these lead to locations and discuss various this visit have to be restricted and significant improvements in the issues. those attending the meeting will quality of observations. have priority. The format of the meeting will be Since then we have had two very to have selected invited talks, A registration form is enclosed, so bright comets which presented open panel discussions, take the time to fill it in now and new problems in observation. contributed talks and poster come and enjoy what should be a There has been a huge growth in sessions. Speakers scheduled to very interesting meeting. The the Internet, enabling rapid appear include Doug Biesecker latest details will be posted on the dissemination of observations and (SOHO comets), Nicolas Biver Section web page. the suspicion that this may bias (visual magnitudes and CO observers. Planetarium programs outgassing beyond 3 AU), Contents using the Guide Star Catalogue Stephane Garro (French archival now give observers precise finder observations), Dan Green (comet Comet Section contacts 2 charts enabling them to observe photometry), Eleanor Helin Section news 2 much fainter comets than in the (comet searching/discovery at Tales from the Past 3 past. Palomar and with NEAT), Gary Professional Tales 4 Kronk (Cometography), Brian Review of observations 6 These new problems need new Marsden (amateur contributions), Comet hunting notes 8 solutions and hopefully discussion Herman Mikuz (CCD Comet History (Part 1) 9 BAA COMET SECTION NEWSLETTER 2 THE COMET’S TALE
Comet Section contacts
Director: Jonathan Shanklin, 11 City Road, CAMBRIDGE. CB1 1DP, England. Phone: (+44) (0)1223 571250 (H) or (+44) (0)1223 221400 (W) Fax: (+44) (0)1223 362616 (W) E-Mail: [email protected] or [email protected] WWW page : http://www.ast.cam.ac.uk/~jds/
Assistant Director (Observations): Guy Hurst, 16 Westminster Close, Kempshott Rise, BASINGSTOKE, Hampshire. (and also Editor of RG22 4PP, England. The Astronomer magazine) Phone & Fax: (+44) (0)1256 471074 E-Mail: [email protected] or [email protected]
CCD Advisor: Nick James, 11 Tavistock Road, CHELMSFORD, Essex. CM1 5JL, England. Phone: (+44) (0)1245 354366 E-mail: [email protected] or [email protected]
Photographic Advisor: Michael Hendrie, Overbury, 33 Lexden Road, West Bergholt, COLCHESTER, Essex, CO6 3BX, England Phone: (+44) (0)1206 240021
Subscription to the Section newsletter costs £5 for two years, extended to three years for members who contribute to the work of the Section in any way. Renewals should be sent to the Director and cheques made payable to the BAA. Those due to renew should receive a reminder with this mailing.
Section news from the Director
Dear Section member, Panther, 504 from Tony Tanti, On passage I was able to complete 370 from Guy Hurst, 351 from I returned from my 11th visit to the drafts for papers on the comets of Werner Hasubick, 225 from Antarctic in March. It was a very 1995, 1996 and 1997 and an Melvyn Taylor, 224 from Michael busy stay at Halley station where I outline of 1998 which will appear Gainsford, 171 from Gabriel was forecasting for our aircraft in the Journal in due course. I Oksa, 151 from Michael Hendrie, operations in addition to my also entered another 2267 136 from Frank Ventura, 125 from expected tasks of installing a new observations into the Section Sally Beaumont, 104 from George automatic weather station and database, this time of the long Alcock and 98 from James Fraser. carrying out an inspection and period comets of the 1980s. This Over the years many non and calibration of the instrument task is now almost completed and former BAA Members have also which measures ozone. The I only have to enter the contributed observations, in forecasting was quite successful observations of these long period particular TA contributors and the and we had no aborted flights comets which solely appeared in Australian comet section, during the 8 weeks of operations. TA. I have not typed up all the including Andrew Pearce (1187), observations in the files because John Bortle (989), Martin Lehky On the flight down to Antarctica I some had already been sent to the (697), Herman Mikuz (625), had a window seat (thanks to a ICQ by Michael Hendrie and I did Alexandr Baransky (621), Bjorn kindly RAF airman) and was able not want to duplicate his typing. I Granslo (481), David Seargent to see the spectacular return of the suspect, however, that I may not (475), Graham Keitch (460), Leonids. At its best we saw one hold all the observation forms Vittorio Zannotta (410), Graham fireball every 10 seconds and I from some observers and that they Wolf (406), Jose Aguiar (375), logged over 300 meteors. The may have gone missing before I Reinder Bouma (364), Atilla peak was much earlier than took over as Director. If anyone Kosa-Kiss (334), Chris Spratt predicted by the experts so who wants a list of magnitude (316) and Paul Camilleri (281). knows where the best location for observations that I hold, please let For most observers these are not the 1999 return will be. me know. the full total that they have made as it excludes those sent to the I saw a number of other interesting The computer archive currently ICQ prior to the commencement phenomena during my stay: a has over 26,000 visual magnitude of the archive. If any readers brilliant halo display which observations by 617 observers at would like to add to their totals by included Hevelius’ parhelia, the 338 cometary apparitions. 117 sending me observations in ICQ parhelic circle and a observers have made only one format either via email or on circumzenithal arc with observation, 376 fewer than 11 floppy disc I’ll be very pleased to supernumery colours, a fogbow, and only 54 have made more than include them. miraging, iridescence on clouds, a 100. Major contributions include 40 knot blizzard and a very weak 2433 from myself, 884 from As described on the front page, we aurora. Albert Jones, 549 from Roy are hosting the International BAA COMET SECTION NEWSLETTER 1999 April 3
Workshop on Cometary from the following BAA Bopp (1995 O1), Spacewatch Astronomy in August, and I hope members: Sally Beaumont, David (1997 BA6), Meunier-Dupouy to see as many of you there as Briggs, Denis Buczynski, David (1997 J2), Mueller (1998 K1), possible. Don’t miss it, who Clegg, Werner Hasubick, Guy LINEAR (1998 K5), LINEAR knows where the next one will be! Hurst, Nick James, John Lewis, (1998 M2), Larsen (1998 M3), John Mackey, Gabriel Oksa, LINEAR (1998 M5), Williams Visitors who have indicated that Jonathan Shanklin, David Strange, (1998 P1), LONEOS-Tucker they will be coming include Jose Melvyn Taylor and Alex Vincent (1998 QP54), P/LINEAR-Mueller Aguiar (Brazil), Alexandr (1998 S1), LINEAR (1998 T1), Baransky (Ukraine), Doug and also from: Alexandr P/Mueller 6 (1998 U2), P/Jager Biesecker (USA/UK), Giuseppe Baransky, Sandro Baroni, John (1998 U3), LINEAR (1998 U5), Canonaco (Belgium), Jose Bortle, Reinder Bouma, Stephen Spahr (1998 W1), LINEAR (1998 Carvajal (Spain), Tim Cooper Getliffe, Roberto Haver, Aymen W3), P/ODAS (1998 X1), (South Africa), Stephane Garro Mohamed Ibrahem, Andreas P/LINEAR (1998 Y1), P/Li (1998 (France), Dan Green (USA), Kammerer, Heinz Kerner, Atilla Y2), Tilbrook (1999 A1), Werner Hasubick (Germany), Kosa-Kiss, Martin Lehky, Jean- Hermann (1999 D1) and Li (1999 Michael Jager (Austria), Gary Claude Merlin, Herman Mikuz, E1). Kronk (USA), William Liller Andrew Pearce and Seiichi (Chile), Don Machholz (USA), Yoshida (apologies for any Many of the fainter comets were Brian Marsden (USA), Herman omissions or miss-classifications). observed only by Seiichi Yoshida Mikuz (Slovenia), Charles Morris who is using a CCD camera on an (USA), Andrew Pearce Comets under observation were: 18 cm reflector to very good (Australia), James Scotti (USA), 4P/Faye, 10P/Tempel 2, effect. I hope to see many more David Seargent (Australia), Chris 21P/Giacobini-Zinner, CCD observations from UK Spratt (Canada), Patrick 29P/Schwassmann-Wachmann 1, observers in the next edition, Stonehouse (USA), Kesao 37P/Forbes, 52P/Harrington- though I can't set an example as Takamizawa (Japan). Abell, 59P/Kearns-Kwee, my camera has been 'borrowed' to 60P/Tsuchinshan 2, 65P/Gunn, help test equipment for Gemini! Since the last newsletter (which 74P/Smirnova-Chernykh, was incorrectly numbered volume 88P/Howell, 93P/Lovas 1, Jonathan Shanklin 6 instead of 5) observations or 95P/Chiron, 139P/Vaisala- contributions have been received Oterma, 140P/Bowell-Skiff, Hale- Tales from the Past
This section gives a few excerpts rather than the meteors forming appeared in Bulletin No 283 of the from past RAS Monthly Notices, from comets. At the New South Wales branch. Details BAA Journals and Sky & Conversazione (an evening of this also appeared in Sky & Telescope. exhibition meeting) Mr Telescope. The March Journal Crommelin gave a lecture on has a report of a lecture given by 150 Years Ago: Francis De Vico comets and recommended more Dr J G Porter to the Newcastle-on- died on 1848 November 15. He use of photography in the Tyne Astronomical Society. At discovered 6 comets and was observation and discovery of this time the 'sandbank' theory of awarded the King of Denmark's comets. In the intervals between comets was popular and he lectures, the Blue Anglo- suggested that Halley's comet Gold Medal four times in 1846 for 13 his telescopic discoveries. He Hungarian Band played music and might consist of 3x10 tons of died of typhus on a visit to there was the chance to view the blocks of meteoric material England and was buried in the exhibits. A note on comet seeking scattered over a space about 20 cemetery of the Roman Catholic recommends the use of one eye for miles in diameter. [Giotto showed chapel in Chelsea. solar observing and the other for that the comet was a single comets and nebulae, and never nucleus x miles long, weighing 100 Years Ago: An interim looking at strong light such as the some x tons]. Sky & Telescope report on Brooks' comet 1898I sun or electric arcs. was running a series of articles appears in the December Journal. entitled 'Terminology Talks'. It was conspicuous in early 50 Years Ago: The November Several of these focussed on November and the reports suggest meeting had several reports on the comets. In December there was a that it was a little fainter than eclipse comet, which was one of short article on the great comet of M13. [only Messier objects were the brightest of the century 1882, including some used for comparisons, a practice (further reports appeared in Sky & recollections from Americans who that is not recommended today.]. Telescope). Next month, Dr had seen it. [Perhaps older In the January Journal Mr Merton gave a talk on comets. In readers would like to contribute Crommelin reported that plates response to a question he recollections of the Eclipse comet, taken to determine the Leonid commented "We do need careful or other bright comets seen over radiant had also revealed a new observations of its magnitude. 25 years ago]. An explanation of comet. Ten comets were observed Most of those who sent the first comet terminology again likened in 1898, a record, beating that of reports appear to have been so the comet's nucleus to a swarm of 1858 when eight were observed. moved at the splendid sight this meteorites extending over a few In March a review of "Remarkable comet made that they omitted to thousand miles, with considerable Comets" by W T Lynn, noted that record precise information of space between the individual comets were probably attracted physical details." The January particles. Finally 1948 equaled into the orbit of meteor swarms, Journal contains an abstract of a the record number of comets with paper on cometary statistics which 14. BAA COMET SECTION NEWSLETTER 4 THE COMET’S TALE
Professional Tales
Many of the scientific magazines the model infers the dust-loss rate clearly between the signal from have articles about comets in them over a limited size range, up to 1 the nucleus and that from the and this regular feature is intended mm sized grains, and because the coma. The lightcurve of the to help you find the ones you've power-law index of the differential nucleus indicates that it is a highly missed. If you find others let me size distribution ranges between - elongated body rotating with a know and I'll put them in the next 3.5 and -4.0, so that most of the synodic period of 25.0 +/- 0.5 hr. issue so that everyone can look dust mass was ejected in the Assuming that the nucleus has a them up. largest boulders that Hale-Bopp geometric albedo of 4% and is a was able to eject. The dust prolate spheroid with a rotational Jonathan Shanklin ejection velocity close to the axis pointing in the direction observations, between 7 and 4 determined by Sekanina (1979), The following abstracts (some AU, was close to 100 m s(-1) for we derive that its semi-axes are shortened further for publication) grains 10 mu m in size, much 4.4 +/- 0.3 km and 1.8 +/- 0.15 are taken from the Cambridge higher than that predicted by R. F. km. The corresponding fractional Conference Network (CCNet), Probstein's theory, thus confirming active area of similar to 8% which is a scholarly electronic previous results of Neck-Line suggests a moderately active network devoted to catastrophism, photometry. This result is an comet. The highly anisotropic but which includes much indicator of CO superheating with coma is dominated by a strong information on comets. To respect to a free sublimating CO sunward fan, and the dust subscribe, contact the moderator ice, in agreement with the high production rate exhibited signs of Benny J Peiser at observed CO velocity. The temporal variability throughout
The information in this report is a April when it is in Ophiuchus and worth monitoring with CCD synopsis of material gleaned from it should reach 10th magnitude in cameras on a regular basis. IAU circulars 7030 – 7138 and June. It is closest to the Earth in The Astronomer (1998 October – July (0.65 AU) when it could be 37P/Forbes will be 13m between 1999 March). Note that the 9th magnitude and UK observers April and June. Andrew Pearce figures quoted here are rounded should be able to follow it until picked up the comet at 13.5 in the off from their original published August, but it then moves too far second half of March. accuracy. Lightcurves for the south. More southerly observers brighter comets are from may be able to observe it until the 52P/Harrington-Abell was observations submitted to The end of the year as it fades. discovered in outburst at 12th Astronomer and the Director. A magnitude by Alain Maury, full report of the comets seen 21P/Giacobini-Zinner, the parent Observatoire de la Cote d'Azur, on during the year will be published comet of the October Draconid CCD images taken on July 21.1. in the Journal in due course. meteors, remained visible until It slowly faded, but then March, though most observers lost underwent a second outburst in 4P/Faye was observed several it in December. Observations October that peaked some 29 days times over the winter as it slowly show the comet brightened very before perihelion, which was in brightened to around 13th mag. rapidly with distance from sun and late January. This is the seventh Perihelion is not until May, but earth changing in step. The 214 observed return of the comet since this is a poor return and further observations give a light curve of its discovery in 1954 and it has observations are unlikely, though 8.3 + 5 log d + 11.4 log r. never became brighter than 17th observers with large apertures may magnitude at previous returns. glimpse it in the autumn. Normally it would have been Comet 21P/Giacobini-Zinner expected to get no brighter than 10P/Tempel 2 makes its 20th 8 15th magnitude at this return, but th observed return since its discovery 9 peaked near 10 magnitude at the by William Tempel (Milan, Italy) turn of the year. as a 9th magnitude object in 1873. 10 Several unfavourable returns were 11 Observations received so far (90) missed in the earlier years. The 12 give an uncorrected preliminary orbit is very stable, which is one 13 light curve for the second outburst reason why it is a favoured target magnitude Observed of 10.9 + 5 log d + 0.0299 abs(t - for planned spacecraft missions. 14 T + 28.5) In 1983 the IRAS satellite 15 detected an extensive dust trail 16 Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Comet 52P/Harrington-Abell behind the comet. 1998 - 1999 9
Traditionally the light curve is 10 regarded as highly asymmetric 29P/Schwassmann-Wachmann 1 11 with a late turn on. There is a has frequent outbursts and over rapid rise in brightness as the past couple of years seems to 12 perihelion approaches, which be more often active than not, 13 continues more slowly for a though it rarely gets brighter than 14 couple more weeks after magnitude Observed 12m. It is possible that its pattern 15 perihelion, followed by a slow of behaviour is changing. This decline until activity switches off. year Andrew Pearce detected a 16 An alternative view is that the 17 major outburst at the end of Aug Sep Oct Nov Dec Jan Feb Mar Apr May light curve is linear with a peak March. 1998 - 1999 about a month after perihelion, which at this return occurs in early It is at opposition in May on the September. borders of Hydra and Libra and 59P/Kearns-Kwee was observed reaches solar conjunction in by Werner Hasubick in January at With a 5.5 year period alternate November. Observers are 15th mag. This is rather brighter returns are favourable and this is encouraged to check the comet at than expected and it could reach one of them. A CCD observation every opportunity over the 12th mag towards the end of the by Seiichi Yoshida in late March th apparition, although it will remain year. put it at 18 mag. The comet may at low altitude for UK observers be picked up in large telescopes in for several years to come. It is BAA COMET SECTION NEWSLETTER 1999 April 7
60P/Tsuchinshan 2 is yet another Hale-Bopp (1995 O1) is now a far suggest a preliminary light faint object imaged by Seiichi telescopic object, but still well curve of 5.1 + 5 log d + 5.8 log r. Yoshida at 16th mag, which is as placed for Southern Hemisphere bright as it will get. observers as it loops round the Large Magellanic Cloud. Comet Meunier-Dupouy (1997 J2) 65P/Gunn remains on view to Somewhat to my surprise I was 9 CCD observers, although it is only able to glimpse it in 20x80 17th mag. binoculars from the Falkland 10
Islands in mid November at 10.5 11 Another faint object is but it will reach 13th mag by the 74P/Smirnova-Chernykh which end of this year. The observed arc 12 doesn't reach perihelion until now covers 1349 days with January 2001 but has already been observations made on 734 days. magnitude Observed 13 th imaged by Seiichi Yoshida at 16 The equation -0.69 + 5 log d + 14 mag. 7.66 log r fits daily means very well, but there are long period 15 MayJunJulAugSepOctNovDecJanFebMarAprMayJunJulAugSepOctNovDec 88P/Howell reached a peak variations about this mean light 1997 - 1998 magnitude of around 10 in the curve of around a magnitude, autumn, but was essentially a which are shown plotted with an southern hemisphere object. The offset of -2. It is currently a little Mueller (1998 K1) was imaged 33 observations received so far brighter than indicated by the by Seiichi Yoshida over the give a preliminary light curve of equation. winter, but is now fainter than 18th 8.8 + 5 log d + 0.0319 abs(t - T - mag. 27.8) Comet Hale-Bopp (1995 O1) LINEAR (1998 K5) was a little -4 fainter and a little more diffuse in Comet 88P/Howell -3 -2 mid October compared to the early 9 -1 autumn. By the end of October it 0 1 was still 14th mag, but becoming 10 2 larger and more diffuse and faded 3 11 4 rapidly in November. The light 5 12 6 curve is very unusual and the 7 comet's absolute magnitude seems 8
13 mean) (daily magnitude Observed 9 to have peaked some 73 days after
Observed magnitude Observed 10 14 perihelion. The combination of 11 12 changing distance from earth, with 15 SepDecMarJunSepDecMarJunSepDecMarJunSepDecMar 1995 - 1999 the late peak in brightness kept the 16 magnitude nearly constant from Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar 1998 - 1999 July to October. Spacewatch (1997 BA6). The orbit of this comet is very The 71 observations analysed give 93P/Lovas 1 was quite well a preliminary light curve of 13.1 + th eccentric, with a period near 4500 observed and faded from 13 mag years and a semi-major axis of 5 log d + 0.0298 abs(t - T - 73.0). at the turn of the year. The 53 several hundred AU. Currently it observations give a preliminary th is 13 mag and is at high southern Comet LINEAR (1998 K5) light curve of 9.3 + 5 log d + 13.8 declination. It is heading for log r perihelion at 3.4 AU in 1999 11 December when it may be around 12 12th mag. 13 Comet 93P/Lovas 1 14 12
Comet Spacewatch (1997 BA6) 15 13
12 16 Observed magnitude Observed
14 17 13 18 15 14 19 Jun Jul Aug Sep Oct Nov Dec Jan
Observed magnitude Observed 16 15 1998 - 1999
17
Observed magnitude Observed 16
18 LINEAR (1998 M2) was imaged Aug Sep Oct Nov Dec Jan Feb Mar Apr May 17 1998 - 1999 a couple of times by Seiichi
18 Yoshida over the winter, but was Dec Jan Feb Mar Apr May too faint for most other observers. 1998 - 1999 Comet/Asteroid 95P/Chiron will be 16m when at opposition in late Larsen (1998 M3) was also imaged by Seiichi Yoshida, this May in Libra. Seiichi Yoshida Meunier-Dupouy (1997 J2) th imaged it near 17th mag in the first faded away and no observations time at 18 mag. quarter of the year. were received after December. The 359 observations received so
BAA COMET SECTION NEWSLETTER 8 THE COMET’S TALE
LINEAR (1998 M5) was at recorded it visually at near 15th 7038, 1998 October 25]. Nick perihelion in January at around mag earlier in the autumn. James imaged the comet on 10th magnitude and moved north October 26. I observed it on from Lyra, passing very close to P/LINEAR-Mueller (1998 S1) October 29.1, making it around the pole in mid March. At this faded from 14th mag in November 12.5 in the Northumberland point its motion effectively to 16th mag in February. refractor x105, DC s3 and cancelled out the earth's rotation diameter around 1'. It reached a and imaging was possible with a LINEAR (1998 T1) was very broad peak of 10th mag fixed mounting. Heading south it discovered during survey work between December and February. passes through Camelopardalus whilst still a long way from and Lynx, reaching Cancer mid perihelion. Several observers Observations received so far (94) year when it will have faded to recorded it over the winter whilst give a preliminary light curve of 13th magnitude. It will then be near 14th mag. The light curve is 9.8 + 5 log d + 0.0201 abs(t - T + too faint and close to the sun for not very well defined yet, but it 27.8). This suggests that it will further observation. should reach 9th magnitude when it now fade quite rapidly. is at perihelion in June, though it Observations received so far (225) will not be visible from the UK. give a preliminary light curve of Comet Jager (1998 U3) 6.2 + 5 log d + 7.4 log r LINEAR (1998 U1) is yet another 8 comet discovered by LINEAR. The object, discovered on October 9 Comet LINEAR (1998 M5) 18, was reported as asteroidal and 10 9 fast-moving, and a request for further observations was placed on 11 10 The NEO Confirmation Page.
Observed magnitude Observed 12 11 From the confirmatory
observations, made at four 13 12 observatories on October 20 and 21, it quickly became clear that 14
Observed magnitude Observed 13 Nov Dec Jan Feb Mar Apr May the object had a retrograde, nearly 1998 - 1999
14 parabolic orbit. Referring to the observations made with the 0.65- 15 m f/3.6 reflector at the Ondrejov Aug Sep Oct Nov Dec Jan Feb Mar Apr May P/Spahr 1 (1998 U4) was 1998 - 1999 Observatory on October 20.9 UT, discovered by Timothy B Spahr of P. Pravec noted that a faint tail the University of Arizona on was visible on individual 3-min October 27.4 on CCD images Williams (1998 P1) was exposures with a clear filter. The taken with the Catalina Sky recovered after perihelion by tail, extending 16" in p.a. 60 deg, Survey 0.41-m f3 Schmidt. It was Andrew Pearce in late November was confirmed on co-addition of 17th mag and was confirmed by but its rapid fade had already six frames. [IAUC 7033, 1998 Spacewatch Telescope images. begun and it was nearly 10th mag. October 21]. The comet is faint [IAUC 7042, 1998 October 29]. This fade continued, though some and distant and past perihelion. The preliminary orbit is a distant observers reported surprisingly elliptical one and the comet did bright magnitudes as late as P/Mueller 6 (1998 U2) was not become any brighter. March. discovered by Jean Mueller on plates taken by herself on Oct 21.3 LINEAR (1998 U5) was another The 82 observations received so (and with K. Rykoski on Oct. 22) object discovered by LINEAR that far give a light curve of 5.1 + 5 with the 1.2-m Oschin Schmidt was later identified as a comet. log d + 15.5 log r. Telescope in the course of the [IAUC 7044, 1998 October 31]. Palomar Outer Solar System On November 1.18 I estimated it Ecliptic Survey. The comet had a at 12.3, rather brighter than 1998 Comet Williams (1998 P1) strong condensation and a short, U3. It brightened explosively and th 6 faint tail to the southeast. [IAUC reached 8 mag just over a 7035, 1998 October 22]. 7 fortnight later. Prediscovery images from 8 September 14 were found in 9 LONEOS data and the comet is an Comet LINEAR (1998 U5) 10 intrinsically faint periodic object 7 11 found at a favourable opposition. 8
Observed magnitude Observed 12 Seiichi Yoshida made a single 9 13 observation in December when it th 10 14 was 17 mag. 11
15 12 Aug Sep Oct Nov Dec Jan Feb Mar Apr May P/Jager (1998 U3) was 13
1998 - 1999 Observed magnitude Observed discovered by TA correspondent 14
Michael Jager on 16- and 9-min 15
Technical Pan film exposures with 16 LONEOS Tucker (1998 QP54) a 0.25-m f/2.8 Schmidt camera. was another target for Seiichi 17 th The comet had a 1'-2' coma with Nov Dec Jan Feb Mar Apr Yoshida, and was recorded at 16 condensation and a tail several 1998 - 1999 mag in December. Martin Lehky arcmin long in p.a. 275-281 deg and Werner Hasubick also and was around 12th mag. [IAUC BAA COMET SECTION NEWSLETTER 1999 April 9
Observations received so far (119) perihelion. [IAUC 7057, 1998 observing in poor conditions at give a preliminary light curve of November 23] Klet on Dec. 7.9, remarked on a 6.1 + 5 log d + 28.9 log r. possible 6" coma. Although it faded quite quickly, LINEAR (1998 W3) The very few observations were made LINEAR Team discovered an The object's cometary nature after December object that had unusual motion on seems now reasonably assured and November 25.3 and placed the it has a period of 9.55 years P/LINEAR (1998 VS24). On information in The NEO [IAUC 7064, 1998 December 7]. Confirmation Page. On reporting Seiichi Yoshida was able to further examining the Nov. 10-11 th observations, published on MPS astrometric follow-up, G. Hug, observe it at 18 mag shortly after 3154, of an apparently Farpoint Observatory, Eskridge, discovery. unremarkable asteroidal discovery KS, noted the object's appearance from the LINEAR program, G. V. was probably cometary, a point P/ODAS (1998 X1) The Williams made identifications confirmed by other observers on Observatoire de la Cote d'Azur- with isolated sets of observations request from the Central Bureau, Deutsches Zentrum fur Luft und from Visnjan on Oct. 24, 28 (the and by the near-parabolic Raumfahrt Asteroid Survey latter having been published on retrograde orbit, which showed it (ODAS) discovered an 18th MPS 2894 as one of two objects to be a distant object. [IAUC magnitude comet on December that were both erroneously 7063, 1998 November 28]. 15.17 with the 0.90-m Caussols identified with 1998 UD19) and Seiichi Yoshida was able to image Schmidt camera. The orbit is of Nov. 26. The resulting orbit was it on several occasions and Martin short period (6.8 years), with Lehky also recorded it visually perihelion having occurred in July. very cometary in form, with a th period of 9.6 years. Furthermore, near 15 mag. [IAUC 7067, 1998 December 17]. he recognized that the object had Once again Seiichi Yoshida made an extremely close approach 139P/Vaisala-Oterma (1998 successfully imaged it. (< 0.01 AU) to Jupiter in Oct. WG22) Precise positions of 1939 1971, with additional approaches TN, an apparently asteroidal 140P/Bowell-Skiff (1998 X2). G. to 0.5-0.7 AU in both 1983 and object discovered by Y. Vaisala at V. Williams, Minor Planet Center, 1995. It is a distant intrinsically Turku on 1939 Oct. 7 and rediscovered comet P/1983 C1 (= faint object, so of no concern for observed by him and L. Oterma on 1983c = 1983 II) in the course of the moment. three more nights over a 35-day his processing of two-night arc, were published in 1979 in "asteroid" data obtained by the P/Spahr 2 (1998 W1) Timothy B Turku Obs. Report R10 and on LINEAR program on Dec. 14 and Spahr of the University of Arizona MPC 4811. The orbit 17. The indicated correction to discovered another comet on computation by Oterma suggested the prediction on MPC 27081 November 16.4 on CCD images to her that the object was a comet, (ephemeris on MPC 32547) was taken with the Catalina Sky and in a communication to the Delta T = +17.3 days. [IAUC Survey 0.41-m f3 Schmidt. It was Minor Planet Center in 1981 she 7076, 1998 December 28]. 16th mag but there was no visible remarked that a careful Seiichi Yoshida has again been reexamination of the plates successful at imaging it, at around tail, with the round coma 18" in th diameter [IAUC 7052, 1998 suggested that the object was 16 mag and it could brighten a November 17]. It reached perhaps somewhat diffuse. The little further. perihelion in January and was no introduction to the 1982 edition of brighter than 15th mag on CCD the Catalogue of Cometary Orbits D/LINEAR (1998 Y1) LINEAR images, but visual observers made quotes her conclusion that the discovered another faint periodic it as bright as 14th mag. object was probably a comet, but comet on December 22.31 [IAUC the object was not actually listed 7072, 1998 December 24]. as one. On MPEC 1998-X19, the Perihelion occurred a month Comet P/Spahr 2 (1998 W1) object is identified by S. Nakano, earlier and it is not due to return 12 Sumoto, with 1998 WG22, a 19th for over 100 years. Because it is a mag apparently asteroidal object one apparition comet with a period 13 observed by the LINEAR program which is a substantial fraction of
14 on Nov. 18.26 and 21: the notional upper limit of 200 years it has been given a D/ 15 Fortuitously, this object was designation. Seiichi Yoshida was located only 4' from the result of able to observe it on several Observed magnitude Observed 16 integrating forward from 1939 the occasions between discovery and
17 orbital elements by Brian Marsden early February. on MPC 6815. Further LINEAR 18 observations were made on Nov. P/Li (1998 Y2) Weidong Li, Dec Jan Feb Mar Apr 1998 - 1999 24. On observing the object with Department of Astronomy, the 1.8-m reflector at the University of California at Dominion Astrophysical Berkeley, reported his discovery P/Hergenrother (1998 W2) C W Observatory on Dec. 6.3 UT, D. of a comet in the course of the Hergenrother found a comet on Balam noted (in FWHM 3".1 Lick Observatory Supernova CCD images obtained by Timothy seeing) an 8" coma and a tail Search (cf. IAUC 6627; with the B. Spahr on Nov. 22.10 in the extending 18" in p.a. 260 deg. On participation of M. Papenkova, E. course of the Catalina Sky Survey. Dec. 7.1 W. Offutt, Cloudcroft, Halderson, M. Modjaz, T. Shefler, The comet was 17th magnitude observing between clouds, also J. Y. King, R. R. Treffers and A. and will fade. The comet was a remarked on a tail (or antitail) V. Filippenko). The object was short period one, almost at extending 17" in p.a. 257 deg, but found automatically by the no coma was noted. M. Tichy, Katzman Automatic Imaging BAA COMET SECTION NEWSLETTER 10 THE COMET’S TALE
Telescope in the field of NGC SOHO was quickly disabled again shows an apparent tail in p.a. 1041, but it was immediately by gyro failures. Ground about 120 deg. It is in a distant recognized as a comet by Li, who controllers managed to get round parabolic orbit and will fade, then used the equipment to make a the problems and it returned to the though Seiichi Yoshida imaged it deliberate confirmatory fray in early February when it at 15th mag just over a week after observation, as well as follow-up quickly discovered another Kreutz discovery. observations on the following group fragment. night. [IAUC 7075, 1998 P/Machholz 2 has not yet been December 28]. The comet is Hermann (1999 D1) S M recovered, though recovery is not periodic with a period of about Hermann of the LONEOS team really expected until late spring. It 15.2 years. Seiichi Yoshida has discovered a comet on images may reach 7th magnitude in the imaged it on several occasions at taken on February 20.4 [IAUC late autumn. This comet split into around 16th mag. Martin Lehky 7111, 1999 February 20]. It is an several fragments at its discovery observing visually made it over intrinsically faint short period return in 1994 and both the two magnitudes brighter. comet. It faded after discovery, ephemeris and expected but not before it had been imaged magnitude are a little uncertain. Tilbrook (1999 A1) Justin by Seiichi Yoshida. The date of perihelion is uncertain Tilbrook (Clare, South Australia ) by up to a day and more accurate discovered a second comet on Li (1999 E1) Weidong Li and M. ephemerides will be published January 12.49 with his 0.2-m f6 Modjaz, Department of when the comet is recovered. UK reflector x70. [IAUC 7084, 1999 Astronomy, University of observers should be able to January 13]. Although it had California at Berkeley discovered observe it from November at 10th perihelion inside the earth's orbit a 17th mag comet in the course of magnitude, though more southerly and was relatively close, it was the Lick Observatory Supernova observers may find it a month intrinsically quite faint and faded Search on March 13.18 [IAUC earlier. after discovery. Andrew Pearce 7126, 1999 March 16]. The made some early observations, object was found automatically by For the latest information on reporting it at a little fainter than the Katzman Automatic Imaging discoveries and the brightness of 10th magnitude. Moving south, it Telescope (KAIT), recorded by comets see the Section www page: will not be visible from the Modjaz as a supernova candidate, http://www.ast.cam.ac.uk/~jds Northern Hemisphere. and recognized by Li as a comet. or the CBAT headlines page at Li then used the equipment to http://cfa-www.harvard.edu/ SOHO (1999 C1). Having been make confirmatory observations cfa/ps/Headlines.html restored to operation in October three nights later. The comet Comet Hunting Notes Don Machholz
JULY 1998: At what declination The discovery may be made by discoverers to five, this is now (number of degrees north or visual, photographic, or electronic half the number of Americans (10) south of the equator) do means. The amount an individual who have visually found comets amateur astronomers visually receives depends upon the number since 1975. There are only two discover comets? The finds range of comet finds during the year. other Southern Hemisphere comet from +72 degrees to -62 degrees. For example, in the past twenty discoverers: Austin of New From 1975 to the present, of the years, any individual who found a Zealand and Campos of South 43 comets found in the Northern comet would have received Africa. All 24 comets found by Hemisphere, seven were found between $1500 and $20,000 for these seven men were discovered north of +45 degrees. Sixteen that comet find. south of the celestial equator, 23 were between +20 and +45 being found by only one degrees and the remaining 20 were SEPTEMBER 1998: While comet discoverer. Peter Williams is the found between the celestial hunting I've always recorded the first person to qualify for the equator and +20 degrees. As for number of meteors I happen to Edgar Wilson Award: a cash sum the 34 southern comets, five were observe passing through my field of about $20,000 to be divided up found south of -45 degrees while of view. On June 16 of this year I among all the amateurs who 16 more were between -20 and -45 recorded my 10,000 telescopic discover comets before June 11, degrees. The remaining 13 meteor. The span of time was 1999. Southern Hemisphere comets were 6314 hours over the course of 23 found between the celestial years. The number of meteors I NOVEMBER 1998: As seen from equator and -20 degrees. see per hour in the morning sky the earth, how far are comets averages 1.9 while the evening sky from the sun when first AUGUST 1998: The Edgar averages 0.9. I also record the discovered? This angle, called Wilson Award has been number of artificial satellites I see. elongation, has been calculated for announced for amateurs who The hourly rates for these has the 78 comets found visually by discover comets. A cash award of increased, and now exceeds the amateurs since 1975. It ranges about $20,000 will be distributed meteor rates. I made my 10,000 from 22 to 171 degrees. Over half each June 12 among those finding satellite sighting about a year ago. of the comets have been found comets during the previous year. within 58 degrees of the sun. The rules are few. The comet OCTOBER 1998: Williams' Seventy of the seventy-eight were must be named after you and you comet discovery on August 10 found within 92 degrees of the must be using your own brings the total number of sun. Why are they found at such equipment in an amateur capacity. Australian visual comet small elongations? Not only do BAA COMET SECTION NEWSLETTER 1999 April 11 comet hunters concentrate their in January. In last place is both searches on areas near the sun, but February and April with three Don's Comet Hunting Hours: comets generally become brightest finds each. in those regions. Comet Hunting Hours 1975-1998: MARCH 1999: Five of the last 6468.00 DECEMBER 1998: Williams, seven visual discoveries (covering Jager and Tucker are all now 2.5 years) have been made by Hours January through February eligible for the Wilson Comet Southern Hemisphere observers, 1999: 26.25 award. Each amateur used a all from Australia, and all five different methods to find "their" comets being found south of the Total hours at last discovery (10- comets: visual, photographic and celestial equator. Two were 8-94): 5589.00 CCD. accidental finds (by Williams and Tilbrook), with Tilbrook then Least hours in any month since he JANUARY 1999: Father Leo finding one more and Tabur began comet hunting on 1/1/75: Boethin of the Philippines passed finding two. 4.00 (02/98), 4.50 (01/86), 5.50 away on Sept.15. He was the (02/80) discoverer of Periodic Comet APRIL 1999: Of the 79 visual Boethin (85P/) on Jan. 4, 1975. It comet discoveries since 1975, 30 Most hours in any month since he orbits the sun every eleven years. (38%) have been made in the first began comet hunting: 69.25 half of the year, with 49 finds in (05/76), 63.00 (05/78) FEBRUARY 1999: In which the second half. Subdividing the month do amateur astronomers year into quarters, the first quarter These notes are taken from Comet visually discover the most has 18 discoveries, the second has Comments by Don Machholz, comets? Of the 79 comets found 12, the third has 26 and the last which is published on the Internet. in the past 24 years, 12 were three months of the year yields 23 found in July while 10 were found finds. A Brief History of Comets I (until 1950)
The following text is taken from physics was inaugurated, in sphere in his system of spherical the ESO web page and is adapted particular by the passage of shells and described them as `dry from a major review on Comets, P/Halley in 1835. The next major and warm exhalations' in the upper prepared by Michel C. Festou step forward occurred in 1950 atmosphere. There is no mention (Observatoire Midi-Pyrenees, with the sudden emergence of the of comets in Ptolemy's Almagest, Toulouse, France), Hans Rickman modern picture of comets as being presumably because they were not (Astronomiska Observatoriet, essentially very old solar system considered of celestial origin, but Uppsala, Sweden) and Richard M. objects made of primordial ice and he described them in astrological West (European Southern dust, generally in unstable orbits terms in his Tetrabiblos. The Observatory, Garching, Germany) and intensively interacting with Aristotelian view on comets was and published in the review the solar electromagnetic and dogmatically upheld during the journal Astronomy & corpuscular radiation. Finally, the following millennium; the first Astrophysics Reviews (A&AR) space missions to P/Giacobini- doubts seem to have been (Part I, Vol. 4 pp. 363-447, 1993) Zinner in 1985 and especially to expressed by Thomas Aquinas and P/Halley in 1986 provided the first also by Roger Bacon in his Opus The present account deals with the in situ observations of comets and Tertium from 1267, but like their period up to around 1950. It dramatically widened our predecessors they strongly includes some references to major scientific horizon, but also posed believed comets to be evil omens. papers in this period (by author of many new questions which are yet year of publication), but the to be answered. original version of this review in Astronomy & Astrophysics Before 1950: The main events Reviews must be consulted for the The word comet, now used in all full details about these. European languages, comes from Greek (kometes= `the hairy one'), Introduction The history of but the earliest extant records of cometary astronomy is naturally cometary observations date from divided into five major periods, around -1000 in China and the transitions being marked by probably from about the same Comet 1664 W1 illustrated by important new insights. Before time in Chaldea (on the territory of Stanislaw Lubieniecki in the 1600, comets were essentially present-day Iraq). Ideas about the Theatrum Cometicum, published considered to be heavenly omens true nature of comets are available in 1667. Observations of it lead and were not yet clearly from the time of the rise of to many advances in cometary established as celestial Hellenistic natural philosophy at science. It also presaged the (astronomical), rather than about -550 when the Pythagoreans plague of London. meteorological phenomena in the considered comets to be a kind of terrestrial atmosphere. Then (wandering) planets that were seen Finally, Paolo Toscanelli observed followed two centuries of mostly rather infrequently and mostly P/Halley in 1456 and several other positional measurements with near the horizon in the morning or comets between 1433 and 1472 emphasis on the motions and the evening sky. Aristotle in his with improved accuracy, orbits, lasting until the early 19th Meteorology (ca. -330) relegated inaugurating the renaissance of century, when the era of cometary comets to the lowest, `sublunar' European observational astronomy BAA COMET SECTION NEWSLETTER 12 THE COMET’S TALE after the long period of dormancy. vicinity of Jupiter's orbit or inside became the first comet in which The decisive demonstration was of it. As time passed, a detailed structures were delivered by Tycho Brahe (and concentration of comets moving in extensively observed, in particular confirmed by a few other similar orbits with fairly low by John Herschel, Bessel and observers, especially Michael inclinations and with aphelia close Friedrich G.W. Struve, who Mästlin), on the basis of extensive to Jupiter's orbit became more and described jets, cones and observations of the bright comet more obvious; this concentration streamers, cf. the Atlas by Donn et which first appeared in late 1577. became known as the Jupiter al. (1986). This led Bessel (1836) He showed that the horizontal family. It either called for a to postulate the ejection of parallax of this comet was continuing ejection from Jupiter or material in the direction of the Sun certainly smaller than 15 arcmin, for a mechanism of dynamical which was then somehow forced corresponding to a distance in evolution, called `capture', back in the opposite direction by excess of 230 Earth radii, or four whereby the comets would an unknown repulsive force. times the distance to the Moon. become concentrated into such Feodor A. Bredikhin (quoted by The question of how comets move orbits. It was realized that comets Jaegermann, 1903) further arose as a natural consequence and in general, and Jupiter family developed this interpretation into in 1610, the amateur Sir William members in particular, suffer by the Bessel-Bredikhin' mechanical Lower proposed that they do so in far the largest orbital perturbations model which remained in use until very elongated ellipses, while due to the action by Jupiter, and the late 1950's. Sir Arthur Robert Hooke and Giovanni the restricted three-body problem Eddington (1910), introduced the Borelli suggested that cometary (Sun-Jupiter-comet) therefore fountain model of particle ejection orbits may be parabolic. Georg offered an interesting in which the parabolas represent Dörffel was the first to specifically approximation for the study of the outer envelopes of particle state that the two bright comets their dynamical behaviour. trajectories emitted from the sunlit seen in 1680 and 1681 are one and hemisphere of the nucleus or the same before and after its After Halley, Johann F. Encke was surfaces of high density of matter. perihelion passage, and that it the second to successfully predict One of the repulsive forces acting moved along a parabola with the the return of a comet (in 1822) on the dust was identified by Sun in the focal point. Isaac which as a consequence now Svante Arrhenius (1900) as the Newton in Principia (1687), carries his name. It turned out to radiation pressure by sunlight. applied his new theory of have, and still has, the shortest The corresponding theory was gravitation to show that the 1680 period of all known comets, 3.3 further developed by Karl comet moved in an elliptical, years, and it was soon found to Schwarzschild (1901) and albeit very nearly parabolic orbit arrive systematically about 0.1 extended to molecules by Peter and that it passed only about days earlier at perihelion than Debye (1909). 0.0016 AU above the surface of predicted, even when taking all the Sun. Edmond Halley (1705) planetary perturbations into computed the orbits of a dozen account. Inspired by his well-observed comets and observations of an asymmetric demonstrated the periodical nature distribution of luminous matter in of the bright comet of 1682. the head of P/Halley in 1835, `Halley's Comet', as it was from Friedrich W. Bessel interpreted now on called, was telescopically this as a Sun-oriented asymmetric recovered in December 1758 by outflow and suggested that a non- Johann Palitzsch; this proved gravitational effect might arise due conclusively the validity of to the rocket-type impulse Newton's law of gravity out to the imparted by such an outflow. As a distance of the aphelion at 35 AU, consequence, such perihelion more than three times the distance shifts as observed for P/Encke of Saturn, the outermost planet might arise. known at that time. During the next decades, 18th century cometary astronomy progressively more sophisticated is characterised by the gradual instrumentation became available development of improved methods and the road was opened for a The Section archives contain for orbital computations and at the more physical approach to the many reprints, some dating back beginning of the 19th century, this study of comets. Comet tails were to the early 19th century. This had become a straightforward, if explained by Heinrich W.M. drawing of comet Donati was still somewhat arduous task, in Olbers (1812) and Bessel (1836) made by G P Bond on 1858 particular when planetary by assuming that they were made October 2 using the great perturbations were taken into of solid particles on which was refractor at Harvard Observatory account by means of iterative acting a repulsive force directed and is from the Mathematical corrections. Some basic features anti-sunward. The close Monthly of December 1858. of the orbital distribution of connection between comets and comets were established, e.g. the meteors was demonstrated by The first spectroscopic extremely broad range of orbital Giovanni Schiaparelli (1866, observations of comets were made periods, over which the different 1867) who found that the orbits of by Giovanni Donati (1864) and by objects are scattered. While some the Perseid and the Leonid meteor Sir William Huggins (1868) who comets turned out to have orbits streams coincide with those of visually compared the spectrum of virtually indistinguishable from comets P/Swift-Tuttle (1862 III) comet Winnecke (1868 II) with parabolas, others were confined to and P/Tempel-Tuttle (1866 I), flame spectra and found that the the inner solar system in the respectively. In 1835, P/Halley bands seen in the comet and in the BAA COMET SECTION NEWSLETTER 1999 April 13 flame, now known as the `carbon' suggested that, because the nature of the central source of gas or `Swan bands', were similar. observed cometary radicals and and dust in comets. Transits of Subsequent observations showed ions are not chemically stable, comets across the solar disk had that these bands were present in all these species must be created by never shown any dark silhouette, comet spectra and that carbon was pure photochemistry of more proving the absence of any therefore an important constituent stable molecules residing inside extended, optically thick object. of comets. Spectroscopy soon the nucleus, cf. for instance the Seeing-limited observations of became the standard technique for reviews by Wurm (1943) and comets passing near the Earth studying the light of comets and Swings (1943). In the 1940's, showed a central, unresolved light new emissions were discovered at Swings contributed significantly to source of dimensional upper limits an increasing rate; Baldet (1926) the development of ideas along in the 10-100 km range (Nicolaus published a detailed description of Wurm's line of thinking and his B. Richter, 1963). Upper limits to the spectra of about 40 comets, key role appears to have been cometary masses had been obtained since 1864, together with overlooked in the later literature. estimated for instance from the a complete bibliography of all The presence of CO, C2N2, CH4, absence of evidence for mutual comets observed until that time by CO2, N2 and NH3 was invoked gravitational attraction of the spectroscopy. Schwarzschild and on the basis that CO+, CN, CH, components of P/Biela in 1846 or Kron (1911) studied the intensity CO2+, N2+ and NH were of any influence on the Earth's distribution in P/Halley's straight identified in comet spectra, orbit at very close passages like tail during the 1910 passage and respectively. Swings proposed that of P/Lexell in 1770; in the suggested that the emission could many possible and reasonable end, masses in the 1012 - 1017 kg be explained by the effect of candidates as parent molecules, range were estimated (Whipple absorption of solar light, followed among others CH4 since CH2 was 1961). Comets were obviously by re-emission, i.e. fluorescence. held responsible for the emission small and light bodies, possibly Polydor Swings (1941) solved the recorded in the 4000-4100 A even without a solid nucleus at the long-standing problem of why the interval, as well as H2O, following center. At the end of the 1940's, violet CN bands (3875 A) in the discovery of the OH 3090 A the nature of the nucleus was still cometary spectra did not resemble ultraviolet emission in 1941 by a subject of much speculation and CN laboratory spectra and varied Swings, and despite the fact that no consensus had been reached. In in appearance: because of the the low vapor pressure of water an attempt to put together all crowding of absorption lines in the was considered a serious problem known facts about the cometary solar spectrum, the intensity at the when explaining the observed nucleus, and with particular exciting wavelengths critically presence of the OH emission far attention to the long-standing depends on the doppler shift from the Sun. In 1948, he came problem of explaining the non- caused by the comet's motion very close to actually proposing an gravitational perihelion shifts, relative to the Sun and so icy model for the nucleus by Whipple (1950, 1951) laid the determines the strength of the suggesting that the mentioned foundations for the model of an fluorescence emission lines in the molecules could exist in the solid icy conglomerate, solid nucleus. comet's spectrum; this is now state in the nucleus. Building on the idea dating back known as the Swings effect. to Pierre S. de Laplace (1813) and Swings (1942) also suggested that Bessel (1836), Whipple described 1950 - 1951: Two crucial years molecules similar to those found the nucleus as a mixture of ices A major revolution in cometary in meteorites were possibly stored from which the gases in the coma science took place in 1950-51, in the nucleus by occlusion. This are produced by sublimation in with the formulation within a short idea was quantitatively (and most increasing quantities as the comet time span of three fundamental probably, independently) explored approaches the Sun and the ideas: 1) the icy conglomerate by Boris Yu. Levin (1943), who nucleus surface temperature rises, (`dirty snowball') model of the developed the desorption theory of and meteoritic dust that is released cometary nucleus by Fred outgassing from the surface of from the nucleus when these ices Whipple (1950), 2) the meteoritic material to demonstrate evaporate. This model had the identification from kinematic that his sand bank model for the virtue of explaining at once studies of the existence of a distant nucleus had a solid basis. several observed features: 1) the reservoir of comets, now known as However, although the average large gas production rates, for the Oort cloud, by Jan Hendrik desorption heat, about 6000 which the desorption model was Oort (1950), and 3) the cal/mole, as deduced empirically totally inadequate, 2) the observed explanation of the motions in from the observed jet-like structures in the coma and cometary plasma tails as due to brightness/heliocentric distance the erratic activity, impossible to interaction with the solar wind by relation, was in agreement with the produce if the nucleus were a Ludwig Biermann (1951). laboratory values for the cometary cloud of particles, 3) the observed Interestingly, none of these ideas molecules mentioned above, the non-gravitational forces by means resulted directly from new amount of material that could be of momentum transfer by the observational evidence, and desorbed from a sand bank with an outflow of gas from the nucleus, important parts of them had been expected cometary mass fell far the net effect on the orbital motion proposed earlier, but it was the short of explaining the persistence being dependent, among others, first time that the known facts of comae over several months at on the sense of the nuclear spin were effectively combined to single passages, or indeed, the and the direction of the spin axis, reveal the new picture. survival of comets like P/Halley or 4) the fact that most comets which P/Encke for many apparitions. pass extremely close to the Sun, The icy conglomerate nucleus e.g. the Kreutz sungrazing group, Karl Wurm, in a series of Since the mid-19th century, a apparently may survive such enlightening papers published great deal of research had approaches intact and with little between 1932 and 1939, concentrated on understanding the change after perihelion, and 5) the BAA COMET SECTION NEWSLETTER 14 THE COMET’S TALE fact that comets are the sources of perturbations were carried out at these appendices that make comets meteor streams. Items 2-4 gave several observatories during the so impressive to the layman, and particularly strong arguments for a first decades of the 20th century. astronomers of all times have been solid nucleus rather than a sand They were naturally followed by struck by the fact that the tails may bank structure. statistical considerations about the vary so dramatically from one distribution and dynamical origin object to another. In the early 20th of comets, including the question century, perhaps the strangest of whether or not some comets characteristic was the enormous have `original' hyperbolic orbits repulsive force found to act on (reciprocal semi-major axis straight comet tails in the anti- 1/aorig < 0) and are therefore of solar direction. interstellar origin. The work at the Copenhagen Observatory by Elis Already in 1859, Richard Strömgren (beginning in about Carrington (1859) suspected a 1910) and his associates is typical physical connection between the of such studies and showed the major solar flare observed in the absence of originally hyperbolic morning of Sept. 1, and enhanced orbits, all observed orbits of this magnetic activity on the Earth type having been caused by some hours thereafter. Ideas about planetary perturbations. Sinding the possible existence of a stream (1948) produced a list with the of particles from the Sun, perhaps values of 1/aorig for 21 long- electrically charged, emerged Many of the late 19th century period comets which together with towards the end of the 19th comets showed intricate structure the work by van Woerkom (1948) century, in particular to explain near to the nucleus. These formed the basis for Oort's famous the excitation of molecules and illustrations of 1881 K1 and 1881 paper (1950) on the existence of a ions observed in cometary comae. N1 were made by Otto Boeddicker cometary reservoir in the outer It was also found that cometary using the 3 foot reflector of the reaches of the solar system. The ion tails (formerly Type I) develop Earl of Rosse at Birr Castle, idea of a cloud of distant closer to the Sun than dust tails which is perhaps better known for hypothetical comets, stable against (formerly Type II). However, it deep sky observations. This stellar perturbations, and its was only 50 years later that Cuno reprint is from the Scientific necessity in case many observed Hoffmeister (1943) provided the Transactions of the Royal Dublin comets would have 1/aorig 10000 crucial observations of a gas tail Society for August 1882. AU, had been expressed earlier by aberration of about 6o, i.e. the Ernst J. Öpik (1932). angle between the observed tail The Whipple model quickly won and the anti-solar direction. This general acceptance and was Based on van Woerkom's (1948) was correctly interpreted by gradually refined during the theory of the orbital diffusion Biermann (1951) in terms of following decades. It had, caused by planetary perturbations, interaction between the cometary however, some shortcomings; the Oort found that the number of ions in the tail and the solar wind, main one was pinpointed by comets with very small values of a stream of electrically charged Whipple himself as being the large 1/aorig is much larger than one particles from the Sun with difference between the latent heats would expect, when comparing velocities of several hundred of vaporization of the various ices. with the neighbouring, long-period km/sec. His derived plasma As a consequence the highly elliptical orbits. This suggested densities were unrealistically high, volatile material should be rapidly that many of the comets become since electrons were thought to removed from the surface layer of unobservable after their first accelerate the cometary ions, but the nucleus long before perihelion, passage through the inner solar Hannes Alfven (1957) settled this in contradiction to the observation system. In a subsequent study, problem by introducing the notion of radicals and ions like CH and Oort and Schmidt (1951) of an interplanetary magnetic field CH+ near the Sun. This objection distinguished between `new which is carried along with the was tentatively removed when comets' (those coming directly solar wind. Its existence was soon Armand Delsemme and Swings from the Oort cloud, making their thereafter confirmed by (1952) noticed that almost all first visit near the Sun) and `old experiments onboard some of the parent molecules (except NH3) comets' (those returning on elliptic first spacecraft launched after the required to explain the observed orbits). The former appeared to be space age opened in late 1957 radicals and ions in comets could dustier and brighten more slowly (Lunik I and II, Explorer X, co-exist in the nucleus in the form than the latter. These tentative Mariner II, etc.). Still, for quite of solid clathrate hydrates. In this conclusions have later been some time, cometary ion tails were way, the highly volatile material revisited and modified, and the the only well-distributed solar does not disappear too rapidly and role of stellar perturbations in wind probes in interplanetary is also freed together with less providing new comets has been space and they remain so outside volatile molecules; this explains reconsidered. However, the basic the ecliptic. Another important why the spectrum remains more or concept of the Oort cloud as an result of Alfven's study is that an less similar throughout the comet outer halo of the solar system has ion tail must be considered as part apparition. been substantiated by later studies, of the comet since it is based on improved samples of magnetically connected to the The Oort Cloud Many orbital cometary orbits. cometary head. studies of individual comets with particular attention to the The solar wind The tails of To be continued influence of planetary comets have been the objects of many investigations. It is exactly BAA COMET SECTION NEWSLETTER 1999 April 15
BAA COMET SECTION NEWSLETTER