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.