THE COMET’S TALE
Newsletter of the Comet Section of the British Astronomical Association
Volume 7, No 2 (Issue 14), 2000 October
WHAT IS THE DIFFERENCE BETWEEN ASTEROIDS & COMETS?
From Science-Week via CCNet astronomical units from the Sun, that astronomers should now perhaps due to the influence of consider these objects as members Other than the moons of the massive Jupiter just outside the of highly diverse family: the various planets, the chief small asteroid belt. Until recently, the small bodies of the Solar System. bodies of the solar system are shapes and surface features of comets and asteroids. asteroids were a matter of 2) If all comets were solid dirty conjecture; during the past balls of water ice, then their bulk In general, a comet is a decade, however, significant densities would be approximately kilometre-size chunk of ice and direct observations of asteroids 1 gram per cubic centimetre. But associated dust and debris. The have been relayed back to Earth some comets have apparent low- Oort cloud is an apparent from spacecraft. density structures that are made spherical shell of comets 10,000 from several bits held together by to 100,000 AU from the Sun and Classical astronomers have little more than their own self- the proposed source of comets categorised comets and asteroids gravity. This conclusion arose that orbit the Sun. The cloud is as distinctly different entities with after some comets were observed at the extreme edge of the Sun's different histories and to break up as a result of tidal influence, halfway to the nearest compositions, but recent evidence forces from either the Sun or star, and it is believed that when is blurring the conceptual Jupiter, and more than two dozen the cloud is perturbed by passing boundary between these two other comets have split apart for stars, comets may be sent into a groups of small Solar System no obvious reason at all. In solar orbit. The size and bodies, and there are several addition, comets that have structure of the Oort cloud have newly discovered objects that are apparently transformed from been deduced from statistical considered to be both comets and active to quiescent objects suggest studies of the orbits of comets; asteroids on the basis of their that some cometary bodies do there is no direct evidence for the characteristics. become defunct and join the cloud's existence. Approximately ranks of the asteroids. Low- 900 comets are known. Don Yeomans (California density extinct comets can Institute of Technology, USA) probably explain a significant Asteroids (also called "minor presents a review of recent fraction of the near-Earth asteroid planets") are small rocky objects, research on comets and asteroids population, "so we cannot assume most of which orbit the Sun in a (Small bodies of the Solar that all objects that threaten Earth belt between the orbits of Mars System. Nature 20 Apr 2000 will have the same composition and Jupiter. A few asteroids 404:829), the author making the or structure." follow orbits that bring them into following points: the inner Solar System, and Continued on page 4 several asteroids occasionally 1) Recent observations have pass within a few tens of millions revealed comets in asteroid-like Contents of miles of Earth. Some asteroids orbits and asteroids in comet-like Comet Section contacts 2 are located in the orbit of Jupiter, orbits. Both comets and asteroids Section news 2 and some asteroids have been can evolve from the Oort cloud Tales from the Past 3 detected as far away as the orbit into highly inclined, even Asteroids & comets (cont) 3 of Saturn. There are *retrograde, orbits about the Sun, The Delta Effect revisited 4 approximately 7200 known so orbital behaviour is no better Professional Tales 5 asteroids, and a million asteroids than physical behaviour for Review of observations 10 are believed resident in the Solar distinguishing comets from Prospects for 2001 19 System. The consensus view is asteroids. The author suggests Why study comets 22 that asteroids are composed of that attempts to categorise comets material that failed to build a and asteroids as distinctly planet at a distance of 2.8 separate entities have failed, and 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) or (+44) (0) 1223 571250 (H) E-Mail: [email protected] or [email protected] WWW page : http://www.ast.cam.ac.uk/~jds/ Antarctic contact info c/o British Antarctic Survey, Stanley, Falkland Islands, South Atlantic. Email: [email protected]
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, file on the Internet. It is quite a been received from the following large file, and I intend to produce BAA members: Sally Beaumont, The spring was a fairly quiet time a printed version as well. This Denis Buczynski, Len Entwisle, for comet observing, with nothing should be ready early next year. John Fletcher, Maurice Gavin, within reach of moderate Massimo Giuntoli, Werner apertures. The summer brought Only a few imagers have adopted Hasubick, Guy Hurst, Nick James, comet LINEAR 1999 S4, the format suggested in the last Geoffrey Johnstone, Alastair although observing conditions issue and I would encourage the McBeath, Cliff Meredith, Martin from the UK were often poor in remainder to use it. Just to Mobberley, Terance Moseley, the east and then the comet remind you, the procedure is to Michael Oates, Gabriel Oksa, Roy disintegrated. More details of the name image files as Panther, Jonathan Shanklin, event are described in the review comet_yyyymmddl_obs.img and David Storey, David Strange, of observations. The end of the auxiliary files as Melvyn Taylor, Cliff Turk and year brings another possible comet_yyyymmddl_obs.txt, where Alex Vincent binocular comet in the shape of yyyy is the year, comet is the 1999 T1 (McNaught-Hartley) and comet identifier, obs the first and also from: Jose Aguiar, Mark at least this one is intrinsically three letters of the observers Allison, Alexandr Baransky, brighter than 1999 S4 so there is surname, l a serial number Jeffrey Barham, Nicolas Biver, less chance of it disappearing. assigned by the observer (which John Bortle, Jean-Gabriel Bosch, can be omitted) and img the Reinder Bouma, Nicholas Brown, Michael Oates has continued image format. As an example Christian Buil, Paul Camilleri, scouring the SOHO archives and 1999s4_19991128a_mob.jpg Eddie Carpenter, Jose Carvajal, has now discovered nearly 70 would be the first jpeg image that Clive Curtis, Sauro Donati, R comets out of the SOHO total of Martin Mobberley took of 1999 Ferrando, Stephen Getliffe, Bjorn 204. I've found a couple more, S4 on that date and if he felt that Granslo, Bernhard Haeusler, including one which could have further information was needed Andreas Kammerer, Heinz been observed by large telescopes there would be a supporting file Kerner, Atilla Kosa-Kiss, Martin in the Southern Hemisphere. 1999s4_19991128a_mob.txt. The Lehky, Rolando Ligustri, Pepe Rather surprisingly no SOHO second gif image of Manteca, Michael Mattiazzo, comets were discovered during 141P/Machholz 2 by David Maik Meyer, Antonio Milani, September. Strange on the same date would Andrew Pearce, Stuart Rae, Juan be 141p_19991128b_str.gif. San Juan, Richard Schmude, A partially revised edition of the Carlos Segarra, Oddleiv Skilbrei, Section Guide to Observing Since the last newsletter Vince Tuboly Jean-Francois Comets is now available as a PDF observations or contributions have Viens and the Ageo Survey Team BAA COMET SECTION NEWSLETTER 2000 October 3
(KenIchi Kadota and Seiichi that this issue of The Comet's (Catalina-Skiff) and 1999 Y1 Yoshida) (apologies for any errors Tale is later and less (LINEAR). or omissions). comprehensive than I would like. Any contributions to the next I will again be visiting the Without these contributions it issue will be very welcome. Antarctic this winter, departing in would be impossible to produce mid November and returning in the comprehensive light curves Comets under observation were: mid January. During my absence that appear in each issue of The 2P/Encke, 29P/Schwassmann- I can still be contacted by email Comet’s Tale. At the moment I'm Wachmann 1, 47P/Ashbrook- (see contact details) or you can finding it quite difficult to get the Jackson, 1995 O1 (Hale-Bopp), write to me in the Falkland time to reply immediately to 1997 BA6 (Spacewatch), 1999 H3 Islands. I should have more time letters and emails due to a large (LINEAR), 1999 J2 (Skiff), 1999 for writing whilst I'm on board number of commitments. Please K5 (LINEAR), 1999 K8 ship! be patient and I will try and reply (LINEAR), 1999 S4 (LINEAR), when time permits. My 1999 T1 (McNaught-Hartley), Jonathan Shanklin commitments have also meant 1999 T2 (LINEAR), 1999 U4 Tales from the Past
This section gives a few excerpts nearly a degree in length as seen bilingual, with a paper on Jupiter from past RAS Monthly Notices, by the naked eye, but much longer appearing in French. and BAA Journals Sky. when viewed with the glass. It was seen by all the crew for about 50 Years Ago: A review of a 150 Years Ago: In the May MN twenty minutes, when a cloud paper by O Struve which was in an extract of a letter from obscured it and it was seen no the February S&T appears in the Professor Schumacher to the more." Mr Jenkins unfortunately May Journal. In it the new President on Petersen's comet died at Rio but the master of the hypothesis by J H Oort of a includes "It is very desirable that Maryland established that the distant aggregation of comets was this comet should be observed comet had also been seen on reviewed. This is now known as after its perihelion passage. M November 15 at 7:30 pm at an the Oort Cloud. A report on the Gauss is even of opinion that it is altitude of 48°. This was comets of 1948 appears in the not proved that a comet must, irreconcilable with the expected July Journal. This was a after having passed the return of a long period comet (the forerunner to the present series, perihelion, move in the same orbit great comet of 1556, 1556 D1) but unfortunately only 1946 - as before." In June a note predicted to return in 1848 by Mr 1949 were published. A comment discussed a comet seen by the Hind. [The positions were not on the Eclipse comet of 1948 is Rev. T M Jenkins ("for whose sufficient to calculate an orbit and still true today: "The liberality Georgetown College, the comet is not listed by Kronk magnificence of the brilliant Washington, was indebted for its (1984) or Vsekhsvyatskii] comet, with its 25°-long tail, observatory") on his voyage to Rio seems to have paralysed the Janeiro. On November 28, 1849 100 Years Ago: Nothing much abilities of most observers to when 10°S, 30°W "We saw a of note occurred and the annual make observations of scientific comet to the westward nearly in report in the October Journal value." The 1949 report appeared the track of the sun, about 14° notes "Very few comets have been in the October Journal and above the horizon, as measured observable during the year, and followed the pattern of the others with the quadrant. The nucleus only one has been conveniently with descriptions of observations very distinct, about as large in placed for the possessors of and light curves of well-observed appearance as Mars, the tail telescopes of moderate size in this objects. curved and pointing towards the country." Interestingly the south (SW.), quite bright and Journal in those days was WHAT IS THE DIFFERENCE BETWEEN ASTEROIDS & COMETS?
Continued from Page 1 iron silicates), and nickel-iron sometimes producing spectacular metal. The C-type asteroids are meteor showers in the sky, but 3) Asteroids have been classified most common in the outer part of leaving little evidence on the according to the light reflected the main asteroid belt, and the S- surface of the Earth. The most from their surfaces -- their optical type asteroids are mostly found in common meteorite is the ordinary spectra. Although no two spectra the inner asteroid belt. chondrite, which is composed are exactly alike, most asteroids mostly of rocky silicates, and so fall into one of two groups, the C- 4) Meteorites are asteroid has not experienced the chemical type (carbonaceous) and S-type collision fragments that have differentiation associated with (silicaceous). C-type asteroids fallen to Earth, and as such are melting. Such chondrites are have low reflectance (albedo) and thought to hold clues regarding thought to be some of the most may contain mixtures of hydrated the early history of asteroids. primitive rocks in the Solar silicates, carbon, and organic Because most asteroid fragments System, although their parent compounds. S-type asteroids are rocky, they can survive the asteroid type is not clear. On 22 have higher albedos and can passage through the atmosphere March 1998, and ordinary contain pyroxene (silicates of the Earth. In contrast, debris chondrite was observed to fall to containing magnesium, iron, and from comet streams nearly always Earth by 7 boys in Monahans, calcium), olivine (magnesium and burns up in the atmosphere, Texas (US), and within 48 hours BAA COMET SECTION NEWSLETTER 4 THE COMET’S TALE the meteorite was under beginning of the Solar System, must have had flowing water examination at the Johnson Space approximately 4.6 billion years within its interior structure. Far Center in Houston, Texas. ago. This suggests the presence of from being the dry rocky bodies Laboratory analysis of the liquid water on the parent they were once believed to be, it Monahans meteorite detected salt asteroid of this meteorite, and would seem that some asteroids, crystals embedded with water in unless this water derived from a along with comets, might be the form of brine, and the salt collision with a salt-bearing icy significant sources of water. crystals were dated to the very comet, the parent asteroid itself Comment's on "IWCA II Method-Related Brightness Estimate Differences and the Delta Effect by Joseph N. Marcus"
Charles S. Morris, Associate Editor, ICQ
Joe Marcus and I have been at of performing multiple regression has never been published and each other's throats for most of on correlated variables. If two certainly not in a refereed journal. the last couple of decades, mostly variables are strongly correlated, (If I am wrong, Joe, send me a in a friendly way. The long as r and delta often are for reprint.) It is difficult to review standing disagreement on the comets, it is impossible to or comment on a theory that is delta effect (or lack of it) has been unambiguously and correctly put forth in bits and pieces in the primary thorn in our scientific separate the computed unrefereed publications, much of relationship. That being said, this parameters. I used solving the it in Comet News Service of little rant by Joe concerning my light curve equation with a delta which Joe was author, reviewer, talk at the IWCA II should win a effect term included as an and editor. I have suggested prize for being grossly off-topic. example of this problem. It is a many times, by the way, that Joe valid example. Joe correctly publish his theory in the ICQ or My talk at IWCA II had almost pointed out that you can check the other refereed publications to no nothing to do with the delta-effect correlation coefficients to avail. theory. In the amateur determine whether or not r and community, there are many delta are significantly correlated. 2) For every case of the delta observers who produce very The bottom line is that you can effect being observed in light professional observations. not *routinely* solve for the curves, the observed effect was However, when amateurs attempt "delta effect" coefficient without just as likely to have been caused to do research with the data confirming that that r and delta by other observing circumstances collected (and publish papers), are not significantly correlated. If (poor location in the sky, etc.). they often do very poorly. In you do, your results are, at best, Even the case that everyone large measure, this is because suspect and, at worst, simply points to, C/1979 Y1 (Bradfield), they have never been through the wrong. This is a valid example as the best example, has an experience of publishing a real because on some occasions I have alternative explanation. I had a research paper. At the ICQ, we seen *general* light curve long string of observations that treat submitted papers in the same analyses that included the delta suggested that this comet had the manner as other professional effect (not by Joe) that have characteristics of a flare in research journals. The papers are ignored this potential problem. brightness near closest approach sent to anonymous referees who [All of Joe's extensive wordage to the Earth. The value of n can review the paper and offer proving that this concern doesn't change after a brightness flare. comments and suggestions to the apply in specific cases misses the This would explain the observed author. Often amateurs get easily point completely.] light curve. What about comets frustrated when their paper is that should have had a significant reviewed and it is suggested that For using this example, I received delta effect, C/1983 H1 and additional work is required before a lengthy rant by Joe in The C/1996 B2, for instance. My it can be considered for Comet's Tale concerning one of analyses show no sign of such an publication. The point of my talk his favourite topics, the delta effect. I'm sure that Joe has at the IWCA II was to point out effect. explanations for this, as well. common mistakes made by amateurs doing research and Comments on the Delta Effect. 3) I do not agree with Joe (as he writing papers. One of the goals suggests in his rant) that "the best of the ICQ is to publish useful 1) If you listen to Joe, you would way to look for a delta effect, is research articles produced by think that the delta effect is a not through the light curve itself." amateurs without sacrificing fully accepted theory, it is not. If it doesn't show up in the light professional standards. I had The delta effect in comet light curve, why should we care about hopped to encourage this with my curve research is applied to visual it? This is one of those ignore the talk. observations by a limited number data arguments, if theory is of researchers, mostly amateur. correct (and of course, it must be), In my talk, I discussed the use of The references in their papers are who cares if the data actually statistics because statistical to Joe's work, mostly to his Comet shows the effect? analysis is the basis for most News Service articles. That is the papers submitted to the ICQ. One problem. To my knowledge, Joe's Before leaving this subject, I want example (out of many presented complete version of the delta to state that I do not rule out the in the talk) involved the dangers effect/magnification effect theory possible existence of a delta BAA COMET SECTION NEWSLETTER 2000 October 5 effect. Joe does make some International Comet Quarterly perhaps you will submit compelling arguments for his would reject a paper simply something now? theory, particularly when applied because it dealt with a subject to the instrument effects problem. such as the delta effect. Daniel [Interestingly the latest issue of Accepting that his theory might Green, ICQ editor, and I go to A&G has a letter relevant to this be valid for the instrument effects, great pains to be fair to all subject (Astronomy & does not necessarily mean that the submissions made to the ICQ. Geophysics, 41, 5.8, October delta effect is real, however. I do This is particularly true where we 2000). The author, John not know for a fact that applying may disagree with the author(s). McFarland, claims that C/1999 magnification is exactly the same Papers are reviewed by a number S4 (LINEAR) shows an 'Opik Law' thing as bringing an object closer of different referees, not just us. (delta effect) and refers to papers when one observes a comet, for We would welcome a well-done published by E J Opik in the Irish instance. paper on the delta effect, even Astronomical Journal between from you Joe. I have tried to get 1963 and 1977. I will attempt to Finally and most importantly, I Joe to submit such an article to review these in the next issue. was greatly offended at the the ICQ for many years. Joe, Jonathan Shanklin.] implication by Joe that the Professional Tales
Many of the scientific magazines found at unusual things happened to the have articles about comets in http://abob.libs.uga.edu/bobk/ solar wind. The first odd feature them and this regular feature is cccmenu.html to be noticed was a dramatic drop intended to help you find the ones in the number of protons at you've missed. If you find others ULYSSES'S SURPRISE TRIP Ulysses, which was reported in let me know and I'll put them in THROUGH COMET'S TAIL 1998 by another team of scientists the next issue so that everyone PUTS HYAKUTAKE IN led by Dr Pete Riley, then of the can look them up. RECORD BOOKS RAS Press Los Alamos National Laboratory. Notice from Jacqueline Mitton, They mentioned that a comet I've received two reprints from could explain some aspects of the Zdenek Sekanina about the Comet Hyakutake, a bright comet odd results. SOHO sungrazing comets. The seen by many people in 1996, first looks at the distribution of developed the longest comet tail Comet nuclei are small bodies the comet fragments and deduces ever recorded. At 570 million km that were formed when our solar from the fact that several comet (360 million miles) it beat the system Was young. They are pairs have been observed that low previous claimed record of 330 typically a few kilometres across, velocity fragmentation has million km (206 million miles) and are composed of a mixture of probably occurred after perihelion held by the Great March Comet of ice and dust. When their orbits and perhaps all the way to 1843. [Not really, one is a visual bring them close to the Sun, the aphelion. The second looks at observation, the other by rise in temperature makes them their tails and finds no evidence spacecraft] The discovery was release gas and dust. The tiny for electrostatic repulsion, so that made recently, when Dr Geraint dust particles are pushed away only gravity and solar radiation Jones and Professor Andre from the Sun by the pressure of pressure control the form of the Balogh of Imperial College, sunlight, forming a dust tail. The tail. He finds evidence for London, together with Dr Tim gas particles eventually become microscopic silicate dust particles, Horbury of Queen Mary and electrically charged, forming ions. which stopped being produced Westfield College, London These ions join the solar wind some 20 - 30 solar radii pre- analysed 1996 data from the flowing away from the Sun, perihelion. Ulysses spacecraft. Their analysis forming an ion (or plasma) tail. of the magnetic field data When Jones and colleagues The following abstracts (some returned from Ulysses on 1 May looked closely at the data returned shortened further for publication) 1996 led them to conclude that from Ulysses's magnetometer are taken from the Cambridge Ulysses had passed through a instrument at the time, they Conference Network (CCNet), comet's tail on that date. They realised that the solar wind's which is a scholarly electronic then found that the tail belonged magnetic field lines displayed a network devoted to catastrophism, to Comet Hyakutake. The herringbone pattern - a sign that but which includes much discovery is reported in the the centre of whatever Ulysses information on comets. To journal 'Nature' on 6 April 2000. had crossed had been moving subscribe, contact the moderator slower than its edges. This is Benny J Peiser at The joint European Space expected at comets, because the
of the most phase-darkened As Bob indicates, the study of the PHYSICAL PROPERTIES OF objects known. The surface is also motions of comets is also THE NUCLEUS OF COMET rougher than that of most complicated by the effects of the 2P/ENCKE Y.R. Fernandez, asteroids, The visual geometric loss of material associated with C.M. Lisse, H.U. Kaufl, S.B. albedo is 0.05 +/- 0.02, within the the sublimation of ices. One can Peschke, H.A. Weaver, M.F. range found for other cometary indeed be suitably wary of active A'Hearn, P.P. Lamy, T.A. nuclei. (C) 2000 Academic Press. comets. But, as he says, it is also Livengood, T. Kostiuk: ICARUS clear that there are *inactive* 147: (1) 145-160 SEP 2000 COMETS MAY BE A WORRY comets, therefore BUT ARE STILL RATHER indistinguishable from asteroids We report a new study of the in appearance. Of course, if they nucleus of Comet 2P/Encke, PREDICTABLE From Brian G. are truly inactive, either having which the CONTOUR spacecraft Marsden lost all their ices or having the is scheduled to encounter in ices completely smothered by November 2003. During the Certainly, Bob Kobres is right to nonvolatile material, their comet's close approach to Earth in point out the close approach of motions are quite gravitational. July 1997, we measured the mid- Lexell's Comet to the earth in We in fact know of some comets infrared thermal and optical 1770, despite the fact that this that are only mildly active, and scattered continua with data from comet had a perihelion distance of we have seen that their motions the TIMMI instrument (imaging) 3 AU prior to its Jovian encounter are affected little, if any, by at the ESO 3.6-m telescope three years earlier. I used a outgassing. Much cometary (wavelength lambda from 8 to 12 somewhat fictionalized version of outgassing is in fact rather mu m), the ISOPHOT instrument the Lexell story in my predictable. (photometry) aboard ISO (3.6 mu presentation of some spoof m less than or equal to lambda "eighteenth-century IAU Might we be missing such activity less than or equal to 100 mu m), Circulars" at an NEO conference on what we think of as asteroids and the STIS instrument in Sicily seven years ago. We when they are near perihelion? (imaging) aboard HST (5500 must indeed be aware that comets That is something I have Angstrom less than or equal to can surprise us in unusual ways. wondered about from time to lambda less than or equal to time, particularly when the 11000 Angstrom). The optical But Bob speaks of PHOs. perihelion distance is small images show the nucleus with Appropriately homonymous enough that the object can not very little coma contamination, though this term may be, I have then be observed in a dark sky. and the ISO photometry allowed not advocated its use for comets. What one *can* say is that the us to separate the comatic and At the U.N. NEO conference in orbits of well-observed, small- nuclear contributions to the ESO 1995 I introduced the term PHA perihelion objects like Icarus and images. We used the Standard for an asteroid with an orbit Phaethon are completely Thermal Model for slow rotators coming within 0.05 AU of that of compatible with point-mass to calculate an effective nuclear the earth (and of absolute dynamics (including relativistic radius of 2.4 km +/- 0.3 km. The magnitude 22.0 and brighter, terms, of course), even though the comet's mid-IR light curve although maybe we need now to former is just coming up its 46th implies a nuclear rotation period extend this to intrinsically fainter passage some 28 million km from of 15.2 h +/- 0.3 h, although some objects) but remarked that the the sun since discovery. subharmonics of this also satisfy corresponding PHC was not a the data. If we assume that the useful concept. This was This is not to say that an nucleus is a triaxial ellipsoid in precisely because almost all "asteroid" could not surprise us in principal short axis rotation with asteroids would not switch from this way, to the extent of making the axis direction in 1985 as PHA to non-PHA status (or vice the difference between an impact derived by Sekanina (1988, versa) over the course of a century and a miss a Century hence for an Astron. J. 95, 911), then by or so (and it is quite sufficient to object whose orbit we think we combining our data with light take the earth's orbit to be a fixed know very well. But the predicted curves from the 1980s we find circle for this purpose), whereas miss would surely be enough of a that the nucleus' angular Jupiter can frequently and "near-miss" to interest us, and we momentum vector migrates, dramatically change the paths of still get to monitor the object, making a would-be circle in less the rather smaller number of including its physical appearance, than 81 years, and that one axial known short-period comets, and between now and then, thus ratio is at least 2.6. The nucleus' we need to--and usually can-- steadily improving the prediction optical linear phase coefficient is specifically study such changes. until the outcome is clear. 0.06 mag/degree, making it one Review of comet observations for 2000 April - 2000 October
The information in this report is a observations submitted to The Andrew Pearce managed to spot it synopsis of material gleaned from Astronomer and the Director. A at around 14th magnitude in early IAU circulars 7398 – 7505 and full report of the comets seen July, but there have been no The Astronomer (2000 April – during the year will be published recent positive observations. 2000 September). Note that the in the Journal in due course. figures quoted here are rounded Spacewatch (1997 BA6) is off from their original published Hale-Bopp (1995 O1) is still another 'old' comet still under accuracy. Lightcurves for the being observed from the Southern observation, but it is now brighter comets are from Hemisphere, but only just. beginning to fade. Southern BAA COMET SECTION NEWSLETTER 2000 October 11
Hemisphere observers will be able 13.2 on July 4. 27 observations to follow it for the remainder of received so far give an the year. The uncorrected uncorrected preliminary light preliminary light curve is m = 4.6 curve of 6.7 + 5 log d + 8.2 log r + 5 log d + 9.8 log r from 97 observations. Scattered observations of 1999 K8 LINEAR have continued, with observers estimating it at around 14th magnitude. Now past perihelion, it is at its brightest because the distance from earth is at its smallest. 72 observations give an uncorrected preliminary light curve of -2.1 + 5 log d + 19.7 log r
Brian Marsden issued several orbital updates. Although earlier orbital elements predicted the comet's position to at worst 0'.1, many users were unable to reproduce the ephemeris correctly for themselves because of the Werner Hasubick made a final need to incorporate the couple of observations of 1999 H3 nongravitational parameters. LINEAR in May and June, when These parameters are quite large it was 14th magnitude. for this comet, and their effect on the ephemeris computed back A few further visual observations from the standard 2000 Aug. 4 of 1999 J2 Skiff were made, epoch was augmented by the although the comet was 15th rather small value of Delta. Some magnitude. users also commented on the fact 1999 S4 LINEAR brightened that the eccentricity in the T. Fukushima, T. Nakajima, and quite slowly, which seems to be a nongravitational solution is J. Watanabe, National feature of ‘new’ comets. significantly smaller than that in Astronomical Observatory of Astrometric observations show a gravitational solution, such as Japan (NAOJ), reported that I- that it is making its first visit to that on MPEC 2000-N15. This is band CCD images of comet 1999 the inner solar system and a normal phenomenon and does J2 taken with the NAOJ 0.50-m therefore behaviour in a similar not alter the likelihood that this is telescope showed a dust anti-tail fashion to comet Kohoutek was a "new" comet in the Oort sense. at the large heliocentric distance expected. [MPEC 2000-O07, 2000 July 19] of 7 AU (the comet having passed perihelion on April 5). The earth D. Schleicher, Lowell H. Weaver, Johns Hopkins crossed the comet's orbital plane Observatory; and C. Eberhardy, University, on behalf of the on May 10.4 [IAUC 7415, 2000 University of Washington, used Hubble Space Telescope (HST) May 5] the Hall 1.1-m telescope at Lowell ToO comet team, reports the Observatory to obtain narrowband following results: "HST images of photometry of comet C/1999 S4, the comet show a dramatic with the following averaged increase in activity on July 5, with results: June 10-12, log Q(OH) = the flux in a 0".15 square aperture 28.41, log Q(CN) = 25.54, log increasing by a factor of about 1.5 Af(rho) = 2.83 (cf. IAUC 7342); in just under 4 hr (from July July 13 (seven sets), log Q(OH) = 5.776 to 5.940 UT). During HST 28.24, log Q(CN) = 25.45; log observations one day later (July Af(rho) = 2.55. The equivalent 6.717-6.889), the activity levels log Q(water; vectorial) is 28.42 were decreasing and were about 3 for July 13, and no significant times lower for the final temporal or aperture variations observation, compared to the peak were observed. Significant value from the previous day. The variability was observed during flux in the last HST image (on the June observations, with the July 7.961) was about 7 times gas-production rates on June 11 lower than the peak value being 30--50 percent larger than measured on July 5. On July 7, at on June 10, and then on June 12 least one 'fragment' is seen 0".85 1999 K5 LINEAR is currently dropping to 10 percent less than (460 km, projected) from the around 13th magnitude visually, on June 10. [IAUC 7455, 2000 nucleus in the tailward direction, and has now passed perihelion, at July 16] and a sharp tailward spike of high southern declination. emission is observed, reminiscent Michael Mattiazzo reported it at of the morphology observed during the outburst in C/1996 B2 BAA COMET SECTION NEWSLETTER 12 THE COMET’S TALE
(Hyakutake) in late-March 1996. spectrum is the MEKAL highly condensed and showed the HST spectroscopic data taken on multiple-line emission model typical 'teardrop' form on July July 5 with STIS show evidence (Mewe et al. 1986, A.Ap. Suppl. 23.9 and 24.9 UT, although its for emissions from CO, C, H, O, 65, 511) using solar elemental brightness decreased by a factor and possibly S. S_2, CS, and OH abundances with enhanced of about 3 between the two nights. were detected during STIS oxygen and nitrogen abundances, On July 25.9 the central observations on July 6, and OH, and a plasma temperature of 0.17 condensation was seen to be CS, NH, and possibly S_2 were keV. The EUVE Lexan B count strongly elongated (length about detected on July 7. Preliminary rate at July 14.21 was 0.06 15") in p.a. 80 deg, with a very production rates are 5 x 10**26 count/s in 5400 s, for an flat brightness distribution. The (July 5), 1.4 x 10**24 (July 6), equivalent luminosity of 1 x condensation's brightness faded and 1.2 x 10**29 (July 6) for CO, 10**15 erg/s at 0.16 keV. The further and its length increased to S_2, and H_2O, respectively, but observed emission was found to about 30" and 45"-50" (p.a. 80 the CO and S_2 values could be highly time variable on the deg) on July 26.9 and 27.9, change by a factor of about 2 or order of hours, enhanced by a respectively. On July 27.9, there so, pending final analysis. strong solar flare propagating was no evidence of any local Nevertheless, one firm conclusion radially from the sun." [IAUC brightness peak that would is that CO is strongly depleted in 7464, 2000 July 25] indicate the presence of subnuclei. C/1999 S4, relative to the The expansion velocity of the observed abundances in C/1996 condensation is about 40 m/s, B2 and C/1995 O1." [IAUC 7461, indicating that it is particulate 2100 July 20 (sic)] material and not gas. The gas tail, which virtually disappeared between July 23.9 and 24.9, has reformed as an extension of the major axis of the central condensation." [IAUC 7467, 2000 July 27]
J. Licandro, G. Tessicini, and I. Perez, Centro Galileo Galilei; and S. Hidalgo, Instituto de Astrofisica de Canarias, report that the inner coma of C/1999 S4 I. de Pater, University of appears extremely elongated in California, Berkeley, with M. R. the tailward direction on J, H, and Hogerheijde, M. C. H. Wright, R. K_s images obtained with the 3.6- C. Lisse and D. Christian, Space Forster, W. Hoffman, L. E. m Telescopio Nazionale Galileo Telescope Science Institute; K. Snyder, A. Remijan, L. M. (+ ARNICA camera) at La Palma Dennerl, Max-Planck-Institut fur Woodney, M. F. A'Hearn, P. on July 26.9 and 27.9 UT. There Extraterrestrische Physik; F. Palmer, Y.-J. Kuan, H.-C. Huang, is no clear central condensation, Marshall, R. Mushotzky, R. Petre, G. A. Blake, C. Qi, J. Kessler, but the photometric peak appears and S. Snowden, NASA/Goddard and S.-Y. Liu, report the to move from the anti-tailward Space Flight Center; H. Weaver, detection of HCN from comet border of the coma toward p.a. 81 Johns Hopkins University; B. C/1999 S4 at the Berkeley- deg on July 26.9 and 84 deg on Stroozas, University of California; Illinois- Maryland-Association July 27.9, with a velocity of and S. Wolk, Harvard- (BIMA) Array in autocorrelation 7".4/day (26 m/s). The brightness Smithsonian Center for mode: "The peak antenna of the central coma decreased Astrophysics, report the first temperature in a 130" beam, from J = 8.83 +/- 0.04 on July detection of x-ray line emission averaged over July 21-24 (about 26.9 to 9.46 +/- 0.07 on July 27.9, due to charge exchange between 10 hr total on source), was 3.5 +/- as measured in a 30"-diameter cometary neutrals and solar-wind 1 mK (a signal suggesting an aperture around the peak. Color minor ions using Chandra and outgassing rate a few percent that maps do not show any major EUVE: "Using a 960-s ACIS-S of C/1995 O1). No signal was structure, the mean colors being observation of comet C/1999 S4 detected in cross-correlation mode J-K = +0.61 +/- 0.05, and H-K = on July 14.20 UT, the comet was with the combined Owens Valley +0.12 +/- 0.06 on July 26.9. detected with a rate in the S3 chip Radio Observatory and BIMA These data suggest that a major of 0.3 count/s, with a total data (the virtual Combined Array event has occurred in the nucleus integral flux of 8 x 10**-13 erg for Research in Millimeter-wave of the comet. A. V. Filippenko s**-1 cm**-2 over 0.2-0.7 keV Astronomy). This suggests a and R. Chornock, University of and a total x-ray luminosity of 6 x source size slightly larger than California at Berkeley, report that 10**14 erg/s. The ACIS-S expected for a Haser model." M. inspection of a CCD spectrum spectrum showed a strong line at Kidger, Instituto de Astrofisica de (range 320-1000 nm) of this 570 eV detected at greater than Canarias, writes that nightly comet obtained on July 28 UT 10 sigma, due to charge exchange observations made since July 23 with the Shane 3-m reflector at to O VII. Other lines due to in U, B, V, R, and Z broadband Lick Observatory reveals no clear charge exchange are also present filters with the 1-m Jacobus emission lines superposed on the (e.g., N VI, N VII at 300-500 eV, Kapteyn Telescope show what solar reflection spectrum, unlike O VIII at 650 eV) at lower S/N. appears to be the complete the case in spectra they obtained The best fit to the preliminary disruption of the comet's nucleus: with the same instrument on July "The central condensation was 6 and June 27. There is no BAA COMET SECTION NEWSLETTER 2000 October 13 evidence for the normally strong involved could be estimated by although the brightest part of the CN emission near 380 nm. The further monitoring the tail. coma is now displaced 1' comet's morphology is peculiar, Experience with the past initially tailwards. The tail can be traced lacking an obvious head that is bright comets that later became at least 20'." [IAUC 7472, 2000 brighter than the adjacent tail, headless and disappeared shows August 3] although the leading edge of the that a narrow, bandlike tail--a head/tail combination is very developing synchronic formation- Further to IAUC 7472, M. Kidger sharply defined. S. Nakano, -should survive the head by reports that the limiting Sumoto, Japan, writes that A. several weeks or even longer magnitude for a 5-sigma point Asami (Bisei Spaceguard Center) (Sekanina 1984, Icarus 58, 81). A source detection in the Isaac was unable to find a peak in the very preliminary analysis suggests Newton Telescope images taken comet's central-condensation that the event may have begun as on Aug. 1.9 UT is R = 22.0. He brightness to determine an early as July 23.6 UT and adds that the continued presence astrometric position from a CCD involved submillimeter-sized and of a well-defined leading edge or image taken in fair conditions on larger dust (repulsive point to the coma suggests that an July 28.490 UT with a 0.25-m f/5 accelerations up to 0.024 of the unresolved fragment of the reflector. [IAUC 7468, 2000 July solar attraction). The position nucleus in this position continues 28] angle and approximate length of to release dust. However, this this tail feature are then predicted structure has faded considerably to reach: July 30.0 UT, 90 deg, 2'; since the disruption occurred. Aug. 4.0, 98 deg, 4'; 9.0, 102 deg, Measurements of the coma 7'; 14.0, 104 deg, 10'; 19.0, 105 brightness distribution indicate deg, 12'; 24.0, 106 deg, 15'; 29.0, that the maximum of light is 106 deg, 17'. Especially toward about 75" from the leading border the end of this period, the of the coma. [IAUC 7474, 2000 predicted length probably is a August 5] crude upper bound. If no such tail persists, the comet's upper mass D. Schleicher and L. Woodney, limit should be tightly Lowell Observatory, write: "We constrained, or the amount of dust used the Hall 1.1-m telescope (+ lost in the event did not represent 95"-diameter aperture) at Lowell a substantial fraction of the total Observatory to obtain narrowband mass." [IAUC 7471, 2000 July photometry of comet C/1999 S4 Further to their item on IAUC 30] (centered at the nominal 7468, Filippenko and Chornock ephemeris position; cf. MPEC report that full reduction of their 2000-O02), yielding the following CCD spectrum obtained on July production rates: log Q(OH) = 28 shows that CN emission near 27.4; log Q(CN) = 24.4; log 380 nm is actually present; the Af(rho) = 1.5 (cf. IAUC 7342). CN was not initially noticed in The equivalent log Q (water; the two-dimensional spectrum vectorial) is 27.6. The values are because it spans the entire slit, 8-10 times less than those making it resemble a night-sky measured on July 13 (cf. IAUC emission line. In contrast, the 7455)." [IAUC 7475, 2000 continuum (reflected sunlight) is August 7] visible only on part of the slit, ending abruptly (as mentioned on IAUC 7468). [IAUC 7470, 2000 July 30] M. Kidger, Instituto de Astrofisica de Canarias, reports Z. Sekanina, Jet Propulsion analysis of continued observations Laboratory, reports: "The of C/1999 S4 at La Palma: "A unusually large nongravitational 100-s exposure in R, taken by R. forces found by B. G. Marsden Corradi and N. O'Mahoney (Isaac (MPEC 2000-O07) suggest that Newton Group of Telescopes) on comet C/1999 S4 was a trailing Aug. 1.9 UT with the Wide Field fragment of a more massive Camera on the 2.5-m Isaac comet that has been moving in Newton Telescope, shows no the same orbit, arrived at evidence of a nuclear perihelion long (centuries?) ago condensation or subnuclei within H. Weaver, Johns Hopkins but (not surprisingly) was missed. the coma. The seeing (measured University, and R. West, Trailing fragments of known from a short exposure at the same European Southern Observatory, comet pairs have a tendency to airmass) was 1".5. It is thus on behalf of a large group of sudden disintegration (e.g., highly improbable that any collaborators, report the following Sekanina 1997, A.Ap. 318, L5). fragments of the nucleus of results: "Hubble Space Telescope If much of the comet's mass did significant size exist within the (HST) images taken during Aug. indeed dissipate into a cloud of coma. The coma shows a similar 5.167-5.396 UT and Very Large dust in the recent event, as structure to that reported Telescope (VLT) images (image suggested by M. R. Kidger (IAUC previously, with a well-defined quality about 0".6) taken during 7467) and others, the total mass sunward boundary to the coma Aug. 6.978-6.999 revealed about similar to the point of a lance, BAA COMET SECTION NEWSLETTER 14 THE COMET’S TALE a dozen active fragments, most of between July 20 and 21, caused a I picked up the comet in my 20cm them located within about 20" of brief brightening of the comet, LX200 x75 on June 7.05, it was the western tip of the dust tail (cf. followed by a more rapid fade, mag 9.9, DC3, coma diameter IAUC 7474). The correspondence although the professionals persist 1.1'. I did not seen again for 34 between fragments in the HST in giving a later date. Indeed days due to a lengthy spell of and VLT images is generally very there is evidence from the light cloudy weather over eastern good, but the brightest fragment curve that fading may have England. I saw it again on July in the HST image is not seen in started as early as late June. 11.94 it was 7.4 in 20x80B, coma the VLT image, indicating rapid Hubble images taken on August 5 diameter 3.1', DC5. Unusually it variability in the activity levels. show the the comet fragmented cleared as it became dark on July The dynamic nature of the into a number of cometisimals, 14 and I made another fragments was further highlighted confirming the concept that observation on July 14.9, the by a dramatic change in the comets are a loose aggregation of comet was 7.1 in 20x80B, DC5, appearance of the fragments in smaller bodies, cemented together coma diameter 3', tail 20' in pa VLT images taken during Aug. by ice and dust. Further images 310. On July 16.9 the comet had 9.976-9.996, when they were taken the next day by the ESO brightened to 6.8 in 20x80B barely detectable. Although the VLT show significant changes to despite the nearly full moon. It latter images were taken under the distribution of the was a similar magnitude on July mediocre observational conditions cometisimals. 18.9 and 19.9. It was markedly (image quality about 1"-1".3, thin brighter on July 21.9 than it was cirrus, and nearly full moon), that KenIchi Kadota succeeded in on July 20.9 with a prominent alone seems unlikely to account recovering the comet on May 4, stellar condensation. Observations for the observed changes. A very when he estimated it at 13.0, with 8x30B on July 21.9 gave a preliminary estimate for the R though at very low altitude. mag of 6.0 suggesting it could be magnitude, within a circular Several observers recovered it at seen with the naked eye from a aperture of radius 0".23, of one the beginning of June with C really dark site. No positive well-isolated fragment is about Segarra reporting it at 10.5 observations were made after 24. A completely inactive visually. Rolando Ligustri August 6. fragment with a diameter of 100 imaged it with CCD on June 1 meters observed under these when it was 9.9 and on June 4, conditions (r = 0.79 AU, Delta = June 23, July 1, July 2, July 6, 0.69 AU, Phase = 86o) would July 18 July 20, July 21, July 26, have R about 25.9 (assuming a 4- July 30. Pepe Manteca imaged percent albedo and 0.04 mag/deg the comet on June 9, June 22, phase law). We urge ground- June 28, July 2, July 12, July 14, based observers to continue July 22. Martin Mobberley monitoring the comet and to imaged the comet on June 22 report any unusual changes near when it was about 9th mag and on the 'tip', both in brightness and July 17. Denis Buczynski imaged morphology." [IAUC 7476, 2000 it on June 26, June 27, July 03, August 10] July 04, July 11, July 15/16, July 16/17, July 19, July 23. David Strange imaged it on June 26, 292 observations give an July 21 and on July 25 as it uncorrected preliminary light fragmented. Nick James imaged curve of 9.1 + 5 log d + 5.6 log r it on July 2, July 18 July 19 July 20. R Ferrando imaged it on July 1999 T1 McNaught-Hartley 9, July 28. John Fletcher imaged According to the preliminary it on July 20. Maurice Gavin light curve the comet should imaged the comet on July 16 and reach binocular brightness. also obtained a spectrum. Initially at far southern Christian Buil imaged the comet declinations it will come within and obtained spectra on July 17. range of binoculars in October. It Gabriel Oksa imaged the comet moves far enough north for on July 25. observation by UK observers in December when it reaches perihelion and moves through Professional observations show Hydra, Virgo and Libra. highly variable emissions. The orbit requires large non Andrew Pearce and Stuart Rae gravitional parameters and this picked up the comet at around combined with the faint absolute 13th magnitude in early June. It magnitude suggests that it is a was 12.7 when Stuart Rae small variably active object. As observed it on July 7.7. Recent described above recent observations from Andrew and observations suggest that it may Michael Mattiazzo make it a little have fragmented, though there is brighter than 10th mag. some 'hype' on the topic, for example from Space Science. 26 observations give an aperture Note the amateur observations corrected preliminary light curve suggest that a burst of activity of 5.8 + 5 log d + 7.5 log r BAA COMET SECTION NEWSLETTER 2000 October 15
perihelion in September. There is currently another short window from the Southern Hemisphere. There is some evidence for a secular fading and any observations will help confirm this. Another suggestion 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. The comet is the progenitor of the Taurid meteor complex and may be associated with several Apollo asteroids.
1999 U4 Catalina-Skiff is very A few observers spotted the comet distant, but could brighten to 14th in early August, estimating it at magnitude when at perihelion in around 11th mag. Pepe Manteca 2001. Pepe Manteca imaged the imaged the comet on August 10 comet on August 25. and August 14. The comet was 1999 T2 LINEAR will reach visible in the SOHO C3 perihelion in November, but is coronagraph, but was fainter than already at its brightest. Denis expected and was only 8.8 on September 7.1. It suddenly Buczynski imaged it on 2000 May brightened on September 14 at 31.04 I estimated it as fainter around 15:00 to 6.5. than 13.1 around the same time and Denis' image shows that it was significantly fainter than this.
1999 Y1 LINEAR could reach 12th mag at the end of the year. Pepe Manteca imaged the comet on August 10, August 18, August 25. 19 observations give an uncorrected preliminary light curve of 7.1 + 5 log d + 6.6 log r Comet 9P/Tempel 1 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 Rolando Ligustri imaged the allowed Elizabeth Roemer to comet on August 26. Pepe recover it in 1967. Alternate Manteca imaged the comet on returns are favourable, but perturbations will once again August 9, August 16, August 17, increase the perihelion distance in August 25, August 28, September the middle of the next century. 4, September 5 September 7, This return is an unfavourable September 9 September 10. I one and no observations were observed the comet on September made. It is an important comet to observe as it is a potential target 26.8 and estimated it at 13.6, with Comet 2P/Encke made its 58th for the Deep Impact mission and a small, moderately condensed observed return to perihelion a special request for observations coma. since its discovery by Mechain in has been made. 1786. The orbit is quite stable, 39 observations give an and with a period of 3.3 years It is a difficult target for amateur apparitions repeat on a 10 year uncorrected preliminary, very observation and may be around cycle. This year the comet is not 17th magnitude. There were uncertain light curve of 7.7 + 5 particular well seen, but there was special observing efforts over the log d + 6.4 log r a short observing window from weekends of July 8/9 and August the Northern Hemisphere prior to 5/6 and there was a further one BAA COMET SECTION NEWSLETTER 16 THE COMET’S TALE over September 2/3. Karen Comet 110P/Hartley 3 is another movie I initially didn't spot Meech attempted observations comet which may become visible anything, but then saw the Kreutz from Hawaii over August 19/21. in large apertures towards the end group object moving towards the of the year. sun from the bottom right hand Comet 17P/Holmes Pepe corner of the image. I quickly Manteca imaged this faint comet SOHO Kreutz group comets sent out a message and at almost on August 10. 2000 H2 SOHO (IAUC 7412, the same time got a message from 2000 May 01) Michael Boschat saying that he The space technology mission 2000 J3 SOHO (IAUC 7422, had also found it. Michael Oates Deep Space 1 is on its way to 2000 May 11) sent a message saying that he was comet 19P/Borrelly. 2000 J4 SOHO (IAUC 7426, just downloading the images and 2000 May 19) we had beaten him to it. I then Comet 29P/Schwassmann- 2000 L1 SOHO (IAUC 7439, measured the positions and sent Wachmann 1 is not well placed 2000 June 14) them off to Doug. (SOHO-138) for observation from the UK, but 2000 L2 SOHO (IAUC 7439, may be seen from locations 2000 June 14) I made an independent discovery further south. It passes through 2000 L3 SOHO (IAUC 7439, of SOHO-169 in the closing Ophiuchus and into Sagittarius 2000 June 14) moments of the second test and is in solar conjunction in 2000 L4 SOHO (IAUC 7445, against the West Indies. I December. Unfortunately 2000 June 29) downloaded the C2 loop and in opportunities for UK observers 2000 L5 SOHO (IAUC 7445, the interval between overs had a may be limited, as its altitude 2000 June 29) quick look and spotted a Kreutz does not exceed 11° from this 2000 M1 SOHO (IAUC 7445, comet moving into the frame on country. 2000 June 29) images from 16:00 onwards. I 2000 M2 SOHO (IAUC 7450, mailed Doug at 17:50 and in the This annual comet has frequent 2000 July 08) meantime England inched outbursts and over the past couple 2000 M3 SOHO (MPEC N26, towards victory. I downloaded of years seems to be more often 2000 July 12) the C3 and spotted a comet active than not, though it rarely 2000 M4 SOHO (MPEC N26, moving in towards the sun since gets brighter than 12m. It is 2000 July 12) 08:42 and deduced that it was possible that its pattern of 2000 M5 SOHO (MPEC N26, probably the same one and had behaviour is changing. In the 2000 July 12) already been discovered. England first half of 1998 it was in 2000 M6 SOHO (MPEC N31, won and I sent another message outburst on several occasions and 2000 July 13) to Doug and then lightning struck this also occurred in 1999. The 2000 M7 SOHO (MPEC N31, the local area and there was a randomly spaced outbursts may be 2000 July 13) power glitch and everything went due to a thermal heat wave 2000 M8 SOHO (MPEC N31, down. I restarted the PC and then propagating into the nucleus and 2000 July 13) checked Doug and Maik's page to triggering sublimation of CO 2000 P1 SOHO (MPEC Q08, find that SOHO-169 had been inside the comet. This comet is 2000 August 19) discovered on C3 by Maik. Then an ideal target for those 2000 P2 SOHO (MPEC Q08, there was another lightning hit equipped with CCDs and it 2000 August 19) and I took the hint to quit before should be observed at every 2000 T1 SOHO (MPEC T33, the computer blew up. This was opportunity. Jose Aguiar 2000 October 10) my first discovery from home and reported as possibly being in were discovered with the SOHO although not an original one it is outburst on July 1 LASCO coronographs and have nice to make an independent find. not been observed elsewhere. I also made an independent Comet 47P/Ashbrook-Jackson. They were sungrazing comets of discovery of 171 on July 2, Michael Mattiazzo recovered the the Kreutz group and were not originally not knowing about comet at 14.0 on July 4. 7 expected to survive perihelion. Terry's find, but on checking observations received give an noted that it had been found on uncorrected preliminary light On June 14 SOHO-135 was July 1 so thought it might be a curve of m = 2.1 + 5 log d + 25.9 discovered on C2 by Michael different object. log r. Boschat, Maik Meyer and Xavier Leprette. I had looked a few 2000 G1 P/LINEAR F. Shelly, Comet 75P/Kohoutek may minutes earlier, but failed to spot for the Lincoln Near-Earth become visible in large apertures the comet. Asteroid Research project, towards the end of the year. reports, in connection with the For me success came again on discovery on April 7.45 of a fast- Comet 97P/Metcalf-Brewington June 15. I had been into moving 18th mag object, that Lisa G. V. Williams, Minor Planet Cambridge to set up a display for Brown-Manguso noticed that the Center, identified this comet with the Cambridge Natural History object showed clear cometary an asteroidal LINEAR object of Society Conversazione (an annual activity. [IAUC 7396, 2000 April 19th mag, 1.1 deg from the exhibition) and had then gone 8] Subsequent observations prediction (MPC 31663). The home to mend a puncture. On confirmed that it is a periodic nominal correction is Delta(T) = returning to work I started to comet, with a perihelion distance +3.5 days, but lacks literal download the latest real-time of 1.003 AU and perihelion on meaning because of the 1993 movie sequence, but then had to March 9.8. The period is 5.4 passage <0.11 AU from Jupiter. extract some images of years. The comet passed only 0.10 [IAUC 7487, 2000 September 5] meteorological equipment for a AU from Earth in late February colleague. On returning to the and early March, when it could BAA COMET SECTION NEWSLETTER 2000 October 17 have reached 14th mag, but was (Apr. 27.0 UT), Ondrejov (Apr. 18th mag object was discovered at high southern declination. It is 27.1), and Modra (Apr. 29.0). M. by LONEOS on April 30.38. It is intrinsically very faint. The Hicks (Table Mountain closest to earth towards the end of comet was moved into its present Observatory) reported a 7" central this month, and reaches orbit in February 1987 when an condensation and 20" tail in p.a. perihelion at 1.19 AU in July encounter to within 0.15 AU of about 120 deg on Apr. 29.4. when it will be at a high southern Jupiter made significant changes [IAUC 7410, 2000 April 29] The declination. [MPEC 2000-J56, to the elements. The comet could comet is in a distant parabolic 2000 May 15] potentially have an associated orbit and is just past perihelion. meteor shower. This would be 2000 K1 LINEAR F. Shelly, maximum around March 30 and 2000 J1 Ferris An apparently Lincoln Laboratory, the meteors would appear to asteroidal object of 19th mag Massachusetts Institute of radiate from 5h 08m -16. reported by LONEOS (observer Technology, reported that W. D. Ferris, measurer B. W. LINEAR discovered a comet 2000 G2 D/LINEAR Another Koehn) on May 4.32 that was (LINEAR-47), of 18th mag on 18th magnitude object with posted on the NEO Confirmation May 26.31. [IAUC 7430, 2000 unusual motion that was reported Page has been found to have a May 26] The comet is a distant as asteroidal by LINEAR on April faint 10" tail in p.a. 150 deg (mag one and will fade, though it could 4.39 has been noted by other R = 19.6 in a 5" aperture) on be several magnitudes brighter to observers, following posting on CCD images taken by M. Hicks visual observers than its discovery the NEO Confirmation Page, as with the Kitt Peak 2.13-m magnitude indicates. The comet being cometary in appearance. G. reflector on May 8.3 UT. [IAUC was linked to asteroids LW24 and Hug, Eskridge, KS, reported a 7416, 2000 May 8] The object NF13 observed by LINEAR in diffuse appearance on several will fade. 1999 and a new hyperbolic orbit CCD images taken with a 0.3-m is given on MPEC 2000-K29. reflector during Apr. 21-29, and 2000 J2 SOHO D. A. Biesecker, Klet CCD observations by J. Emergent Information 2000 K2 LINEAR Shelly also Ticha, M. Tichy, and Z. Moravec Technologies, Inc., and Goddard reported that LINEAR discovered (0.57-m reflector) indicated a Space Flight Center, reports another comet (LINEAR-48) on coma diameter of about 6" on observations of another comet the same night. It was a little Apr. 22.9 UT. A 300-s R found in LASCO C2 data on May brighter and showed a tail in p.a. exposure taken by C. 7.24 by M. Oates via the SOHO 240 deg. Ticha reported the comet Hergenrother with the Steward website. The comet brightened to be slightly diffuse, and Observatory 2.3-m telescope on from V = 7.8 on May 7.254 UT to Kusnirak reports a faint tail about Apr. 30 confirms that this object 7.1 on May 7.368, but had faded 20" long in p.a. 220 deg; Galad has a 6" coma and a 20" tail in to V = 8.3 on May 7.452, and it reported cometary appearance. p.a. 117 deg. The comet reached was not seen in the C3 [IAUC 7430, 2000 May 26]. The perihelion on 2000 February 6.1 instrument. No tail was evident. comet will brighten a little. with a perihelion distance of 2.72 Astrometry (measured by AU. [IAUC 7411, 2000 May 1] Biesecker, reduced by B. G. A/2000 LK Another interesting Marsden) and orbital elements asteroid was reported on MPEC A/2000 GH147 The asteroid appear on MPEC 2000-J32; this 2000-L14. Discovered by 2000 GH147 was discovered with comet is evidently not a Kreutz LONEOS, this object has a NEAT on 12 April 2000. It was sungrazer. perihelion distance of 0.11 AU subsequently followed up by many and an eccentricity of 0.95, which observers worldwide, including J. A/2000 HR24 Details of unusual takes it out nearly to Jupiter's Ticha, M. Tichy at Klet, P. asteroid 2000 HR24=1995 XH5 orbit. Kusnirak at Ondrejov, M. Hicks, appear on MPEC 2000-J50. The D. Deaver, at Table Mountain. object was first spotted by A/2000 NL10 This asteroid This 1.5 km (1 mile) asteroid is Spacewatch in December 1995, approaches the sun to 0.17 AU unusual with a high-inclination and then independently and has an eccentric orbit which (50 degrees), high-eccentricity discovered by LONEOS in late takes it out to 1.68 AU. It was (0.48) orbit that takes it from near April this year. Prediscovery discovered by LINEAR on July 10 Mars' orbit to inside Jupiter's. It is images have been found in [MPEC 2000-N28, 2000 July 12]. therefore an extinct comet LINEAR and NEAT data. The Further observations from candidate. [NEAT web page] asteroid has an 11.1 year period, Paolmar from 1952 and 1992 with a perihelion distance of 4.1 have been discovered and an A/2000 GQ132 MPEC-2000-J19 AU and passed 0.76 AU from improved orbit is given on MPEC reported a second cometary Jupiter in 1941 August. The 18th 2000-O17 [2000 July 23] asteroid discovered by NEAT on mag object, which appears stellar, April 12.51. This object of 18th will fade. [MPEC 2000-J50, 2000 2000 O1 Koehn B. W. Koehn, mag is in a 5.9 year orbit with May 13] The encounter with Lowell Observatory, reported his inclination of 30 degrees and a Jupiter made relatively small discovery of a possible 18th mag perihelion distance of 1.5 AU. changes to the orbit. comet in the course of the Lowell [2000 May 06] Observatory Near-Earth-Object A/2000 HD74 Details of unusual Survey on July 20.36. The comet 2000 H1 LINEAR A 19th mag asteroid 2000 HD74 appear on is a distant one and won't become object reported by LINEAR on MPEC 2000-J56. The object has a brighter than 17th mag [IAUC 2000 April 26.39 and posted on high inclination short-period (5 7462, 2000 July 23] MPEC 2000- the NEO Confirmation Page has year) cometary type orbit, but O22 shows the identification, by been noted to be diffuse at Klet shows no cometary activity. The B. G. Marsden, of this comet with BAA COMET SECTION NEWSLETTER 18 THE COMET’S TALE the LINEAR "asteroidal" objects the far side of the Sun and fully 2000 R1 P/Shoemaker-Levy 5 1998 XA_70 and 1999 UJ_10, illuminated. The LINEAR team reported that together with improved orbital The orbit was finally published on one of their objects observed on elements: T = 2000 Jan. 27.35 MPEC 2000-Q09 [2000 August Sept. 6 was cometary, and T. TT, Peri. = 55.11 deg, Node = 19], after Brian Marsden returned Spahr and Dan Green noted that 88.86 deg, i = 148.10 deg to the USA following the IAU this was about 0.6 deg northwest (equinox 2000.0), q = 5.9219 AU, meeting in Manchester. It seems of the prediction for P/1991 T1 = e = 1.0009. [IAUC 7465, 2000 that the IAU had commanded all 1991z = 1991 XXII (MPC 29882, July 25] three senior members of the 39661), corresponding to CBAT to attend the meeting. The Delta(T) = -1.4 day. Following a 2000 O2 P/Kushida C. E. comet had been at perihelion on request from the Central Bureau, Delahodde, European Southern July 30.94 at a perihelion distance D. Balam reported that images Observatory, reports the recovery of 0.054 AU. Potentially it was taken with the 1.82-m Plaskett by O. R. Hainaut and herself of observable from the ground at an telescope of the National comet P/1994 A1 (= 1994a = elongation of 50 degrees in late Research Council of Canada show 1993 XX) with the 3.6-m August, though at a magnitude of this object to have a well- reflector on July 25.33. The near 20. The orbit shows that it condensed coma and a fan-shaped indicated correction to the passed on the far side of the sun, tail extending 30" in p.a. 250 deg; prediction by S. Nakano on MPC so phase effects do not explain the his R magnitude of 18? was 31664 is Delta(T) = -0.10 day. fading. obtained in a 10" aperture. [IAUC Further observations and 7488, 2000 September 7] The improved orbital elements are Further to IAUC 7472, D. 18th mag object will brighten a given on MPEC 2000-O32. Hammer has provided little. [IAUC 7467, 2000 July 27] measurements of a comet detected by the SOHO C2 and C3 2000 R2 P/LINEAR A 19th mag 2000 O3 SOHO I discovered instruments and found by J. D. object reported as asteroidal by another comet at 10:45 (UT) on Shanklin via the SOHO website. the LINEAR team on September July 31. I had given a lecture in The reduced measurements and 3.15, and subsequently posted on the centre of Cambridge and orbits by B. G. Marsden, together the NEO Confirmation Page, has didn't get into the office until with a search ephemeris, are been reported as cometary in after 10:00 (11:00 BST). First I given on MPEC 2000-Q09. G. J. appearance on various CCD checked the emails, including Garradd, Loomberah, N.S.W., exposures: Sept. 7.2 UT, several Antarctic ones which had reports that his search for this condensed 9" coma (D. Balam, data that needed processing. object around Aug. 21.4 UT, out Victoria, 1.82-m reflector); Sept. Then I had a look at various web to about 0.5 deg ahead of its 7.9, object seemed diffuse with a pages, including the latest predicted position, yielding faint east-west tail about 10" long MPECs, finally I had a look at the nothing to mag about 18. [IAUC (M. Tichy, Klet, 0.57-m SOHO real time movies. I first 7479, 2000 August 21] reflector); Sept. 18.51, near- looked at C2; there were no stellar condensation with a fairly obvious Kreutz objects but I noted 2000 OF8 Spacewatch Details of narrow 40" tail in p.a. 90 deg (R. something that appeared to be an unusual asteroid with a 190 H. McNaught, Siding Spring, 1.0- moving opposite to the stars. I year period, a high inclination m reflector + 100-s R frames). quickly found that it was moving orbit and a perihelion distance of The available astrometric consistently and emailed Doug 2.0 AU were given on MPEC observations are given on MPEC and the group with details of the 2000-P03. The 20th magnitude 2000-S04, where orbital elements possible object. I then checked object was discovered by show this to be a short-period C3 in case it was visible and Spacewatch on July 24.32 and comet with perihelion distance of downloaded the real-time gif won't reach perihelion until next 1.39 AU and period of 6.26 years. images to measure the positions. year. It is currently 4.4 AU from It has a very faint absolute I found that it came into view at the Sun and it is possible that it magnitude of 18.0 [IAUC 7492, 21:30 on July 30 and was visible will develop cometary activity as 2000 September 18] until 03:30 on July 31, moving it gets closer. Further horizontally from right to left just observations did indeed show 2000 S1 P/Skiff B. W. Koehn, above the level of the occulting cometary activity and a parabolic Lowell Observatory, reports the disc and below the beehive orbit was published on MPEC discovery by Brian A. Skiff of a cluster. At its brightest (00:06) it 2000-Q43. The comet reaches comet on images from September was around 7th mag. I think the perihelion in August 2001 at 2.2 24.30 taken in the course of the biggest surprise is that no-one AU. The comet could reach 14th LONEOS program. [IAUC 7496, else had picked up this object! mag next summer. 2000 September 25] Prediscovery Subsequently the comet came into observations made by LINEAR on view again, on images from 05:54 2000 Q1 SOHO James Danaher August 26, together with till after 12:00. The apparent discovered a faint non Kreutz additional astrometry on fading around 03:30 may be due object on C3 images from August September 26, are given on to phase effects playing a part. If 28. It tracked diagonaly across the MPEC 2000-S60 and show that it was then between us and the upper left quadrant. The orbit the comet is periodic with a sun it would have zero phase and published on MPEC 2000-Q42 period of 17.1 years. [IAUC 7497, be difficult to see. The phase suggests that it could be visible 2000 September 27] The comet is effect partly explains why many from the ground, but will be a reported as around 15th mag, but Kreutz comets are seen during very faint southern hemisphere may be brighter visually. It is near May as this is when they are on object. opposition in Cetus and will fade.
BAA COMET SECTION NEWSLETTER 2000 October 19
2000 S2 P/Shoemaker-LINEAR reported as discovered by B. A. 2000 S4 Tom Gehrels reported F. Shelly and R. Huber, MIT Skiff on images taken on his discovery of a faint (20th Lincoln Laboratory, reported the September 29.27 by M. E. Van mag) comet on October 2.15 discovery by LINEAR of a 19th Ness in the course of the images taken with the mag comet with a tail in p.a. LONEOS program at Lowell Spacewatch telescope at Kitt about 280 deg, on September Observatory. Skiff described a Peak, noting it to have a 4" tail in 27.44. Confirmation of cometary nearly circular coma of diameter p.a. 170 deg. T. B. Spahr, Minor appearance on September 29.1 15" with moderate condensation. Planet Center, linked it to an was received from P. Pravec and Following tentative linkage by B. asteroidal object observed on P. Kusnirak at Ondrejov (coma G. Marsden, Center for September 23 and 26 reported diameter 0'.2 with a 0'.2 tail in Astrophysics, to one (mag about earlier by LINEAR and then p.a. 260 deg) and from J. Ticha 19) of about 2000 asteroidal found LINEAR observations and M. Tichy at Klet (object objects recorded on September 20 made on September 1. At the diffuse with 14'' tail in p.a. 265 by LINEAR, a tentative request of Gehrels, P. Massey deg). Available astrometry and ephemeris was provided on the obtained images of the object in preliminary parabolic orbital NEO Confirmation Page. This subarcsecond seeing with the 4-m elements (T = 2000 July 27.6 TT, linkage was confirmed by Mayall Telescope at Kitt Peak on q = 1.305 AU, i = 20.2 deg) were observations obtained on Oct. 2 October 3.25 UT, showing the published on MPEC 2000-S67. by J. G. Ries with the 0.76-m comet to have a fan-shaped [IAUC 7498, 2000 September 29] reflector at McDonald structure 4" long spanning p.a. 0- S. Nakano, Sumoto, Japan, then Observatory. Skiff adds that 80 deg. [IAUC 7502, 2000 identified comet C/2000 S2 with observations by L. H. Wasserman October 3] The comet is close to comet D/1984 W1 (Shoemaker 2), with the 1.1-m telescope at perihelion at 2.3 AU and has a the comet now being off from his Lowell Observatory on Oct. 2 period of around 19 years. prediction (cf. ICQ 2000 Comet showed a 14" x 11" coma, Handbook) by Delta(T) = +23.2 elongated east-west. [IAUC 7501, For the latest information on days or about 7.5 deg in sky 2000 October 2] The comet is discoveries and the brightness of position. [IAUC 7499, 2000 periodic, with a period of 40 years comets see the Section www page: September 29] and was at perihelion in mid July http://www.ast.cam.ac.uk/~jds at a distance of 2.66 AU. It will or the CBAT headlines page at 2000 S3 On October 1, B. W. fade. http://cfa-www.harvard.edu/ Koehn communicated his cfa/ps/Headlines.html measurements of a comet, later Comet Prospects for 2001
2001 sees a couple of good BAA office or the Director; a new remaining a morning object. returns of periodic comets. edition is in preparation. Slowly fading as it passes through 19P/Borrelly, which was well Gemini (September), the Leos observed at the last return, is Alphonse Borrelly discovered (October) and into Ursa Major predicted to be the brightest, and comet 19P/Borrelly in 1904 from (November), the comet begins to may reach 9m in the northern Marseilles, France, during a move north more rapidly and autumn. 24P/Schaumasse also routine comet search with a ends the year at 11m in Canes has a good return and reaches 160mm refractor. It was put into Venatici. 10m. Several long period comets its discovery orbit by an encounter discovered in previous years are with Jupiter in 1889, which only Alexandre Schaumasse still visible and there are some made minor changes, and discovered comet poor returns of short period subsequent returns slowly became 24P/Schaumasse during a visual comets. Theories on the structure more favourable. Despite having search with the 400mm coude of comets suggest that any comet had several further moderately equatorial at Nice, France in 1911 could fragment at any time, so it close approaches to Jupiter the December as a 12m diffuse object is worth keeping an eye on some orbit has only changed a little and and it reaches a similar of the fainter periodic comets, the comet will next approach magnitude at average returns. which are often ignored. This Jupiter in 2019. This will be its The 1952 return was very would make a useful project for 13th observed return, with two favourable and the comet reached CCD observers. Ephemerides for poor ones having been missed. 5m, though there may have been new and currently observable At its best return in 1987 it an outburst. The orbit is comets are published in the reached 7.5m. This return is only relatively stable and this will be Circulars, Comet Section a little worse and the brightness its 10th observed return. UK Newsletters and on the Section, should peak at around 9.5m observers may pick up the 13m CBAT and Seiichi Yoshida's web towards the end of September, comet in the evening sky in pages. Complete ephemerides shortly after perihelion. UK February as it brightens on its and magnitude parameters for all observers are likely to first pick way to perihelion. Moving comets predicted to be brighter up the comet as it passes through northwards in Aries, it passes into than about 18m are given in the Orion in mid August when 10m, Taurus in mid March when it International Comet Quarterly though more southerly observers should be a magnitude brighter. Handbook; details of subscription will already have had it under It is at its brightest tracking to the ICQ are available from the observation for a couple of through Auriga at the end of comet section Director. The months. The solar elongation April and early May when it section booklet on comet only slowly increases, but the should be at nearly 10m. Passing observing is available from the comet moves north, although into Gemini we will loose it low BAA COMET SECTION NEWSLETTER 20 THE COMET’S TALE in the summer twilight by the end quite closely to the Earth and will perihelion in late January 2001. of the month. do so in 2011 (0.06 AU) and 2017 If it maintains the level of activity (0.08 AU). At present the MPC seen at the last return it might be 29P/Schwassmann-Wachmann 1 only lists eight approaches closer glimpsed in the morning sky is an annual comet which has than 0.06 AU, and five of these around the beginning of frequent outbursts and seems to are by periodic comets. It was December, although the solar be more often active than not at well observed at its last return in elongation is not good. More the moment, though it rarely gets 1995/96. The comet will be in likely the comet will have brighter than 12m. It spends the the field of the SOHO LASCO returned to a quiescent state and year in Sagittarius reaching coronagraphs in March, though it will not be observed. If an opposition in early July and solar may be too faint to be seen. outburst does occur near conjunction in January 2002. The Observers at low northern perihelion, it is still unlikely to be comet is an ideal target for those latitudes should be able to observe observed as the elongation does equipped with CCDs and it it as it recedes from the sun not become favourable until May, should be observed at every during April and early May. but then the comet could be opportunity. Unfortunately observed for the rest of the year as opportunities for UK observers 47P/Ashbrook-Jackson was it slowly fades. are limited, as its altitude does not discovered in 1948 following an exceed 13° from this country. approach to Jupiter in 1945, The comet's 1930 approach to which reduced the perihelion Earth is ninth on the list of well Horace Tuttle was the first distance from 3.8 to 2.3 AU. determined cometary approaches discoverer of 41P/Tuttle- Although intrinsically relatively to our planet. In May 2006 it will Giacobini-Kresak in 1858, when bright, the large perihelion make another close approach he found a faint comet in Leo distance keeps it faint. Alternate (0.082 AU), when it could again Minor. Nearly 50 years later, returns are favourable, but this is reach 7m or brighter. This small Professor Michael Giacobini not one of them and the comet miss distance makes it a discovered a 13m object whilst will be in solar conjunction after convenient spacecraft target, and comet hunting, which was perihelion in January. The comet the Contour mission is scheduled observed for a fortnight. Andrew may be seen in early January by to intercept it, as well as comets C D Crommelin linked the Southern Hemisphere observers at 2P/Encke and 6P/d’Arrest and apparitions in 1928 and made 13m. possibly a new discovery. predictions for future returns, but Following its outburst in 1995, the comet wasn't recovered and it Professor Arnold Schwassmann 73P/Schwassmann-Wachmann 3 was given up as lost. In 1951, and Artur A Wachmann of is expected to show fresh Lubor Kresak discovered a 10m Hamburg Observatory discovered cometary surfaces, whilst comet in 25x100 binoculars their third periodic comet on 2P/Encke is an old comet and whilst participating in the minor planet patrol plates taken 6P/d’Arrest an average one. With Skalnate Pleso Observatory's on 1930 May 2. Initially of the orbit approaching so closely to program of routine searches for magnitude 9.5 it brightened to the Earth, an associated meteor comets. After further nearly 6m, thanks to a very close shower might be expected, and observations the comet was approach to Earth (0.062 AU) on the come`t has been linked to the identified with the lost comet and June 1. The initial orbit was a Tau Herculid shower, though the a better orbit computed. At the little uncertain and the comet radiant now lies in the Bootes - 1973 return, which was similar to wasn’t found at the next or Serpens region. Strong activity the 1907 return, it underwent a succeeding apparitions until was reported in 1930 by a lone major outburst and reached 4m, 1979. The comet passed within Japanese observer, but little has before fading and then 0.9 AU of Jupiter in 1953, and been seen since then. It is likely undergoing a second outburst. 0.25 AU in 1965. In August that any future activity would be Alternate returns are 1979, Michael Candy reported the in the form of a short-lived unfavourable and this is one of discovery of a comet on a plate outburst, confined to years when them, but the comet has been taken by J Johnston and M the comet is at perihelion. observed at a few of them and it Buhagiar while searching for should be possible to observe it minor planets; this had the 97P/Metcalf-Brewington. near perihelion in January from motion expected for Howard J Brewington of equatorial regions, though it will 73P/Schwassmann-Wachmann Cloudcroft, New Mexico be little brighter than 12m. If it 3, but with perihelion 34 days discovered a comet with his 0.41- undergoes a further outburst, later than in a prediction by Brian m reflector on 1990 January 7. more widespread observation may Marsden. Missed again at the This was subsequently found to be be possible. next return, it has been seen at the the first observed return of last three returns. At the last P/Metcalf (1906 V2), which had 45P/Honda-Mrkos-Pajdusakova return, in 1995, the comet been lost since 1907, though a makes its 10th observed return underwent a major outburst near good prediction for its return in since discovery in 1948 (it was perihelion, reaching 5m when it 1975 had appeared in the Journal. missed in 1959). It has had was only expected to be 12m. A prediscovery image on January several close encounters with Subsequently four components 5 showed the comet at about 15m Jupiter, the most recent in 1983 were observed, though suggesting that it was found which made dramatic changes to calculations by Sekanina during an outburst. The failure to w and W. The perihelion distance suggested that the fragmentation find it during its first few returns has steadily decreased and is now occurred after the outburst. The and also in 1975 and 1983 the smallest it has been for the comet will be brightening towards indicate that it is normally last 200 years. It can approach the end of 2000 on its way to inactive. A close approach to BAA COMET SECTION NEWSLETTER 2000 October 21
Jupiter in 1993 has drastically Several recently discovered and crosses into the Southern altered the orbit and q has parabolic comets will be visible Hemisphere in April. 2000 OF8 increased to 2.6 AU, so that it is during 2001. 1999 T1 (Spacewatch) may reach 14m unlikely to be observable visually (McNaught-Hartley) is the around the time of its perihelion, unless it undergoes another brightest of these comets and but is a Southern Hemisphere outburst. Perihelion occurs in should be fading from binocular object. April, and a substantial pre brightness. It tracks northwards perihelion outburst could bring it through Serpens and Hercules 95P/Chiron is 17m when at within visual range, though the and then loops through Draco opposition in June on the border elongation is poor and gets worse where it will remain visible until of Ophiuchus and Sagitarrius. as it closes in on perihelion. It the autumn. 1999 T2 (LINEAR) CCD V magnitudes of Chiron was recovered by LINEAR in is unlikely to be better than 13m at would be of particular interest as 2000 September, several degrees the beginning of the year and will observations show that its from its nominal position. fade. 1999 Y1 (LINEAR) spends absolute magnitude varies much of the year at around 13m erratically.
Comets reaching perihelion in 2001
Comet T q P N H1 K1 47P/Ashbrook-Jackson Jan 06.5 2.31 7.46 7 5.0 15.0 41P/Tuttle-Giacobini-Kresak Jan 07.0 1.05 5.43 8 7.0 15.0 74P/Smirnova-Chernykh Jan 15.6 3.55 8.49 4 5.0 15.0 73P/Schwassmann-Wachmann 3 Jan 27.8 0.94 5.36 4 5.5 7.0 1992 G3 (P/Mueller 4) Feb 07.9 2.65 9.01 1 11.5 10.0 44P/Reinmuth 2 Feb 20.0 1.89 6.63 8 10.5 15.0 113P/Spitaler Feb 25.9 2.13 7.09 2 12.5 5.0 75P/Kohoutek Feb 27.3 1.79 6.68 3 10.5 10.0 110P/Hartley 3 Mar 21.4 2.48 6.88 2 8.0 15.0 1999 Y1 (LINEAR) Mar 24.1 3.09 5.5 10.0 107P/Wilson-Harrington Mar 26.6 1.00 4.30 5 15.0 5.0 45P/Honda-Mrkos-Pajdusakova Mar 29.9 0.53 5.25 9 10.7 11.1 97P/Metcalf-Brewington Apr 13.7 2.61 10.5 2 4.6 15.0 1993 X1 (P/Kushida-Muramatsu) May 01.2 2.75 7.44 1 8.0 10.0 24P/Schaumasse May 02.7 1.20 8.25 9 7.6 24.2 61P/Shajn-Schaldach May 08.8 2.33 7.46 5 10.0 10.0 51P/Harrington Jun 05.9 1.57 6.77 5 12.0 10.0 86P/Wild 3 Jun 18.6 2.31 6.93 3 8.5 15.0 2000 CT54 (LINEAR) Jun 19.5 3.16 8.5 10.0 1994 A1 (P/Kushida) Jun 27.8 1.43 7.58 1 11.5 2.1 16P/Brooks 2 Jul 19.8 1.83 6.86 14 8.8 15.0 2000 OF8 (Spacewatch) Aug 05.0 2.17 9.5 10.0 82P/Gehrels 3 Sep 03.1 3.63 8.45 3 6.0 15.0 19P/Borrelly Sep 14.7 1.36 6.86 12 7.0 12.7 1987 Q3 (P/Helin) Sep 26.3 2.53 14.1 1 5.0 20.0 1999 U4 (Catalina-Skiff) Oct 28.4 4.92 4.5 10.0 133P/Elst-Pizzaro Nov 23.7 2.64 5.61 3 12.0 10.0 11D/Tempel-Swift Dec 12.1 1.59 6.37 4 13.0 10.0
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)
BAA COMET SECTION NEWSLETTER 22 THE COMET’S TALE
Several other comets return to Looking ahead, 2002 doesn't see LASCO coronagraphs from perihelion during 2001, however any particularly good returns of January 5 to 11. 6P/d'Arrest is they are unlikely to become bright periodic comets. Perhaps the another of 2002's comets, but we enough to observe visually or are most interesting is that of should be able to recover it at the poorly placed. 16P/Brooks 2, 96P/Machholz 1. The orbit is very end of 2001 as it brightens 44P/Reinmuth 2, 82P/Gehrels 3, very unusual, with the smallest past 14th magnitude. 107P/Wilson-Harrington, 1993 perihelion distance of any short X1 (Kushida-Muramatsu) and period comet (0.13 AU), which is References and other sources 1994 A1 (Kushida) have decreasing further with time, a unfavourable returns. high eccentricity (0.96) and a Nakano, S. and Green D. W. E., 51P/Harrington, 61P/Shajn- high inclination (60°). Studies by Eds, International Comet Schaldach, 74P/Smirnova- Sekanina suggest it has only one Quarterly 2001 Comet Handbook, Chernykh, 75P/Kohoutek, active area, which is situated (2000). 86P/Wild 3, 110P/Hartley 3, close to the rotation pole and Shanklin, J. D., Observing Guide 133P/Elst-Pizarro, 1987 Q3 becomes active close to to Comets, (1996). (Helin), 1992 G3 (Mueller 4), perihelion. The comet may be the Marsden, B. G. Catalogue of 1999 U4 (LINEAR) and 2000 parent of the Quadrantid meteor Cometary Orbits, 13th edition, CT54 (LINEAR) are intrinsically shower. It is rarely sufficiently IAU CBAT, (1999). faint or distant comets. well placed to see visually and Kronk, G. W., Cometographia, Ephemerides for these can be this return is no exception. Cambridge University Press, found on the CBAT WWW pages. Although it may be as bright as (1999). 11D/Tempel-Swift has not been 6th magnitude at the end of 2001, Belyaev, N. A., Kresak, L., seen since 1908 and the time of the elongation is only 18°. At Pittich, E. M. and Pushkarev, A. its return to perihelion is perihelion on 2002 January 8 it is N., Catalogue of short Period uncertain by many months. only a few degrees from the Sun Comets, Bratislava (1986). and may be seen in the SOHO Why Study Comets?
Don Yeomans, Jet Propulsion Lab
Life on Earth began at the end of clues to the chemical mixture evolve further. Indeed, we may a period called the late heavy from which the giant planets owe our pre-eminence at the top bombardment, some 3.8 billion formed some 4.6 billion years of Earth's food chain to cometary years ago. Before this time, the ago. If we wish to know the collisions. A catastrophic influx of interplanetary debris composition of the primordial cometary collision with the Earth that formed the Earth was so mixture from which the major is only likely to happen at several strong that the proto-Earth was planets formed, then we must million year intervals on average, far too hot for life to have formed. determine the chemical so we need not be overly Under this heavy bombardment of constituents of the leftover debris concerned with a threat of this asteroids and comets, the early from this formation process - the type. However, it is prudent to Earth's oceans vapourised and the comets. Comets are composed of mount efforts to discover and fragile carbon-based molecules, significant fractions of water ice, study these objects, to characterise upon which life is based, could dust, and carbon-based their sizes, compositions and not have survived. The earliest compounds. Since their orbital structures and to keep an eye known fossils on Earth date from paths often cross that of the upon their future trajectories. 3.5 billion years ago and there is Earth, cometary collisions with evidence that biological activity the Earth have occurred in the As with asteroids, comets are both took place even earlier - just at past and additional collisions are a potential threat and a potential the end of the period of late heavy forthcoming. It is not a question resource for the colonisation of bombardment. So the window of whether a comet will strike the the solar system in the twenty first when life began was very short. Earth, it is a question of when the century. Whereas asteroids are As soon as life could have formed next one will hit. It now seems rich in the mineral raw materials on our planet, it did. But if life likely that a comet struck near the required to build structures in formed so quickly on Earth and Yucatan peninsula in Mexico space, the comets are rich there was little in the way of some 65 million years ago and resources for the water and water and carbon-based molecules caused a massive extinction of carbon-based molecules necessary on the Earth's surface, then how more than 75% of the Earth's to sustain life. In addition, an were these building blocks of life living organisms, including the abundant supply of cometary delivered to the Earth's surface so dinosaurs. water ice can provide copious quickly? The answer may involve quantities of liquid hydrogen and the collision of comets with the Comets have this strange duality oxygen, the two primary Earth, since comets contain whereby they first brought the ingredients in rocket fuel. One abundant supplies of both water building blocks of life to Earth day soon, comets may serve as and carbon-based molecules. some 3.8 billion years ago and fueling stations for interplanetary subsequent cometary collisions spacecraft. As the primitive, leftover building may have wiped out many of the blocks of the outer solar system developing life forms, allowing formation process, comets offer only the most adaptable species to BAA COMET SECTION NEWSLETTER 2000 October 23
BAA COMET SECTION NEWSLETTER