THE COMET’S TALE
Newsletter of the Comet Section of the British Astronomical Association
Volume 13, No 1 (Issue 25), 2006 April
Comets: from Antiquity to the Present Day
An RAS Specialist Notes in square brackets are my on “The Views of Comets before comments. An account of the Newton and Halley”. Early Discussion Meeting meeting also appears in the April observations were for astrology. 2005 December 9 issue of the RAS Journal A&G. In mediaeval times it was a question of what they portended. Professor Iwan Williams and Dr The meeting was held in the Tycho established that comets lay Stephen Lowry organised the lecture theatre of the Geological beyond the Moon. Newton and meeting to commemorate the Society, with an audience of Halley gave us orbits, and there tercentenary year of the around 60. Iwan Williams began was an association between publication of Halley’s ‘Synopsis the meeting by noting that it was comets and meteor streams in the of the Astronomy of Comets’. The 300 years since Halley had 19th century. science programme included published his paper predicting the various aspects of cometary return of comets, and three The Chinese used lunar mansions science including their history, months since the start of real to record comet positions to at links with other solar system cometary science [Deep Impact]. least a degree accuracy. Their minor body populations such as The RAS copy of the paper, along appearance and form were used to Kuiper Belt Objects and near- with Peter Apian’s Astronomicum make predictions of events. Earth asteroids, and some recent Caesareum, published in 1540 Aristotle said that comets moved developments from spacecraft was on display in the Geological in straight lines and were earthly missions. The following notes are Society library. exhalations. The death of Julius my account of the meeting, and Caesar was marked by a comet in may not accurately reflect the The first speaker was Don 44 BC, which appeared after he speaker’s original presentation. Yeomans (NASA/JPL) who spoke had been murdered. When Charlemagne died in 814 there wasn’t a real comet on view, so one was invented and recorded. Broadsides became very popular in the mediaeval period and publicised disasters. In 1456 Halley’s comet was associated with the plague. Some comets were associated with good events, for example the comet wine of 1811.
Contents Comet Section contacts 2 Section news 2 Tales from the past 4 RAS Meeting (continued) 4 Professional tales 8 Review of observations 12 Meeting review 19 The comet of 1532 drawn by Peter Apian
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 221482 (W) Fax: (+44) (0)1223 221279 (W) or (+44) (0) 1223 571250 (H) E-Mail: [email protected] or [email protected] WWW page : http://www.ast.cam.ac.uk/~jds/
Assistant Director (Observations): Guy Hurst, 16 Westminster Close, Kempshott Rise, BASINGSTOKE, Hampshire. (and also Editor of RG22 4PP, England. The Astronomer magazine) Phone & Fax: (+44) (0)1256 471074 E-Mail: [email protected] or [email protected]
Assistant Director (CCD): Nick James, 11 Tavistock Road, CHELMSFORD, Essex. CM1 5JL, England. Phone: (+44) (0)1245 354366 E-mail: [email protected]
Photographic Advisor: Michael Hendrie, Overbury, 33 Lexden Road, West Bergholt, COLCHESTER, Essex, CO6 3BX, England Phone: (+44) (0)1206 240021
The Section newsletter is now free to all BAA Members who make contributions to the work of the Section. The cost for other postal subscribers is £5 for two years, extended to three years for those who contribute to the work of the Section in any way, for example by submitting observations or articles. 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. You can also download the newsletter (in colour) from the Section web page.
Section News from the Director
Dear Section member, comet 73P/Schwassmann- 73P/Schwassmann-Wachmann is Wachmann with my 90mm short proving to be a very interesting I had an interesting visit to the focus refractor that I took on my object, or objects, with over sixty Southern Hemisphere, staying in travels, but observations were fragments having been reported as the Falkland Islands, Bird Island, hampered by clouds. I can I write. The main component King Edward Point and Ascension sympathise with Gill who stayed should become visible to the Island. I managed some on the island for six months in naked eye when it passes close to astronomy, observing comet 1882 and had to move from the Earth in May, however exactly Pojmanski from on board the Georgetown to the inhospitable how many of the fragments will Fishery Protection Vessel Sigma Mars Bay to get decent survive remains to be seen. The whilst on route between the conditions. I walked to the bay numerous fragments do present a Falklands and Bird Island. We (having gained permission to visit naming problem and those also had one clear night at Bird from the US Air Force, who were submitting visual observations Island and I observed the comet very helpful) across a barren should check the observations again in the early hours, in cinder waste in scorching posted on the Section web page to company with two others from the temperatures, which seemed far make sure that they get the ICQ station and a congregation of the worse than the Egyptian desert format correct. I’m afraid that the local fur seal pups, with petrels that we visited to view the majority of reports do need some calling in the background. Leonids. I’ve written some notes editing before they can be on my visit and these are available imported into the archives. In on the web at part this is a problem with some http://www.antarctica.ac.uk/met/j mail systems which insist on ds/notes_from_south_2006.htm. splitting what to them seems long lines, but in other cases is simply a matter of not quite getting the format correct. I had not considered the issue of components when we devised the image naming system, but the The Milky Way at Bird Island IAU system can be used. This just adds the component with a I arranged a stop-over at hyphen, for so use for example Ascension Island on the way 73P-B_20060411_shanklin.jpg or north and spent four enjoyable Mars Bay, Ascension Island 2009F2- days exploring this volcanic C_20100923_shanklin.jpg. It is island. I was able to observe best to follow the standard BAA BAA COMET SECTION NEWSLETTER 2006 April 3 practice and include all relevant predicts to return in August. It is Seiichi Yoshida (apologies for information (eg telescope, camera possible that the Section might be any errors or omissions) for etc) with the image, rather than as granted regular observing time, so submitting observations or a separate file. Visual observers if you have suggestions for contributions since the last also need to double check that suitable targets let me know. newsletter. Without these they are getting the format exactly contributions it would be right – compare what you sent me Apart from the last month or so it impossible to produce the by email with what appears in the has been a very quiet period for comprehensive light curves that observation file on the Section comet observing, but I would like appear in each issue of The web page. Failing to get the to thank BAA observers: James Comet’s Tale. Observations from format exactly right adds Abbott, Peter Birtwhistle, Roger groups that currently do not send considerably to the amount of Dymock, John Fletcher, Massimo observations to the BAA would work I have to do to process the Giuntoli, Werner Hasubick, Guy be much appreciated as they make observations. Hurst, Nick James, Geoffrey a valuable addition to the Johnstone, Albert Jones, Martin analyses. The boundary between comets McKenna, Cliff Meredith, and asteroids has been further eroded with the numbering of 174P/Echeclus, and the distinction is becoming blurred with other solar system bodies. I’m sure that Pluto would be better assigned a cometary designation than a planetary one, but the arguments about whether it is a planet or not (it clearly isn’t!) will rumble on. There are perhaps reasonable grounds for even calling the Saturnian satellite Enceladus a comet – certainly the images showing water jets look remarkably similar to those of spacecraft images of comets.
Perhaps unsurprisingly no-one rose to my challenges in Astronomy Now and the SPA news circular of identifying exactly what comets were P/LINEAR 42 and P/NEAT 18 respectively. This clearly demonstrates how impossible the old naming scheme would have become, and why all astronomers should stick to the simple IAU convention. Richard Miles, Martin Mobberley, Comets under observation Gabriel Oksa, Roy Panther, included: 29P/Schwassmann- We saw a very impressive Malcolm Park, John Punnett, Wachmann, 41P/Tuttle- demonstration of the power of a Derek Rowley, Jonathan Giacobini-Kresak, 2-m telescope at the April BAA Shanklin, Jeremy Shears, 73P/Schwassmann-Wachmann, Meeting, held in Liverpool. We Giovanni Sostero, David Strange, 174P/Echeclus, 2005 E2 had a live session on the Faulkes Cliff Turk, Alex Vincent, Eric (McNaught) and 2006 A1 telescope in Hawaii and took a x- Walker and also: Jose Aguiar, (Pojmanski). second exposure of component B Alexandre Amorim, Alexander of 73P. The BAA has further Baransky, Nicolas Biver, Jean- I have been finding it increasingly sessions on the telescope and I Gabriel Bosch, Reinder Bouma, difficult to produce two issues of intend to ask for selected comets Jose Carvajal, Edwin van Dijk, the newsletter each year, so I plan to be observed on a regular basis. Stephen Getliffe, Vergil Gonano, to move to an annual report giving My thoughts that these should be JJ Gonzalez, Bjorn Granslo, a preliminary review of the a mix of speculative and routine Ernesto Guido, Michael Jager, comets of the year. This will be observations, with perhaps Andreas Kammerer, Heinz published in early January and searches for some of the Kerner, Mark Kidger, Carlos will also include many of the sunskirting comets, and Labordena, Martin Lehky, A regular features that appear in the observations of some of the Lepardo, Rolando Ligustri, newsletter. Subscribers will have brighter comets on their way in Michael Mattiazzo, Sensi Pastor, their subscription extended pro- and out of perihelion. The initial Maciej Reszelski, Jose Reyes, rata. As always the latest news targets might be comets 4P/Faye Juan San Juan, Pepe Manteca, will be available on the Section and 8P/Tuttle, which are the Jose Martinez, Andrew Pearce, web page. brightest periodic comets of the Stuart Rae, Walter Robledo, V next couple of years, and 2002 Santini, Tony Scarmato, Ralf Jonathan Shanklin R5, which Sebastian Hoenig Vandebergh, Tony Ward and BAA COMET SECTION NEWSLETTER 4 THE COMET’S TALE
Tales from the Past
This section gives a few excerpts Neptune, but at 50 kms-1 at with a scare-mongering story of a from past RAS Monthly Notices perihelion. An increase of only future German invasion in 1910. and BAA Journals. 0.5 kms-1 would make the orbit Comet 1906 F1 was discovered parabolic. Discussion of the by Mr David Ross of Melbourne 150 Years Ago: Dr Donati paper raised the point that on March 18. Mr Ross was a contributed a note giving an Pentecoulant was probably wrong Member of the Association and elliptical orbit for comet 1855 L1 in his calculation of the Vice-President of the Victoria (Donati) and suggesting an eccentricity at the last return. It Branch. This was his second identity with a comet seen in 1362 was also commented that there discovery. Other Southern (1362 E1), which had a poorly had been no decent comets since Hemisphere Members who had defined retrograde orbit. [The 1882 and that at least Halley discovered comets were Tebbutt orbit given in the 2005 Catalogue would be good in 1910. During (5), Gale (1), Davidson (1) and of Cometary Orbits gives a period the past month, five comets had Grigg (3). In March Lynn of 252 years]. The annual report been visible. Mr Longbottom had presented a paper on Halley’s of the Council, presented at the taken a 90 minute exposure of Comet and “Zadkiel”. Zadkiel February RAS meeting, records comet 1905 W1 (Schaer), though was Richard Morrison, an that three comets were discovered there was a break in the middle. astrologer who associated all sorts during the year. A report is given Two comets were under of calamities with comet Halley of Struve’s paper in the Memoirs observation at the January over the ages. of the Imperial Academy of meeting. One had been Sciences in St Petersburg on discovered only a couple of days 50 Years Ago: The October observations of Biela’s comet earlier by a former Member of the meeting included a report on with the great Pulkova refractor at Association, Prof. W R Brooks of recent comets, particularly comet its 1852 return. This included Geneva, New York. A new book 1955 O1 (Honda). Dr Merton detailed notes on its two “Remarkable Comets: A brief reminded observers of the rule components. Survey of the most interesting fact which Dr Steavenson had told in the History of Cometary him of many years ago [at least a 100 Years Ago: An extract from Astronomy” by W T Lynn was decade, as a note had been Astronomische Nachrichten (AN) reviewed. The reviewer noted published in the Journal in 1942] notes that perturbation by a ring that it would be suitable for the that in order to obtain reliable of planetoids might explain the “man in the street” who wishes magnitudes of comets you anomalous motion of 2P/Encke, not to appear to his associates should use the smallest telescope as this couldn’t be explained by a quite ignorant of matters that will show the comet clearly. resisting medium. The connected with comets. In AN, In this case some observers had Presidential address also referred Dr Cohn discusses whether one or used 20cm reflectors when they to the motion of Encke’s comet three comets had been visible in should have used binoculars. and he suggested that future 1742. [Kronk notes that a second Michael Hendrie showed some returns might throw some light on comet is likely, with a third slides of the comet, including one the mystery. [We now think that it possible]. In March the President with a 60 minute exposure. Roy is related to the rotation of the said that it was curious that there Panther exhibited some drawings, nucleus and asymmetric was an epidemic of comets of and two drawings by George outgassing]. The West of great perihelion distance. It might Alcock appear in the report. Two Scotland Branch (Glasgow) had a be that many had passed papers in the March Journal relate lecture on comets at its November unobserved since 1729 [Comet to predictions for early (ie pre 239 meeting, where the three types of 1729 P1 had a perihelion distance BC) appearances of comet Halley. comet tails were ascribed to of 4.1 AU]. It was probable that [None have been confirmed]. At metallic elements, hydrocarbons we should see only a large comet the March meeting Dr Merton and hydrogen. At the December that had such a great perihelion opened a discussion on the meeting Dr Smart read a paper on distance. There might be many observation of comets, which was “The Orbit of Halley’s Comet”. small ones that passed through followed by contributions from He noted that the comet spends perihelion unobserved by us. Mr Steavenson, Alcock and M B B less than six months north of the Maunder noted that the Daily Heath. ecliptic, and travels at 1.7 kms-1 Mail had brought up Halley’s between aphelion and the orbit of comet as an omen in connection RAS Meeting
Continued from Page 1. curved paths. Halley determined was recovered by Palitzsch in orbits using Newton’s theory and 1758, although at the time Tycho showed that comets lay predicted the return of several. Palitzsch did not realise it was the beyond the moon. Kepler Applying planetary perturbations long awaited comet. however observed that comets led to some uncertainty and he were ephemeral and said that became increasingly less Encke linked several previously therefore they must move in confident on his famous observed comets and showed that straight lines. Galileo thought prediction. Clairaut refined the they were all the same. He also similarly. Hevelius thought that calculations with Lalande and noted that it returned 2.5 hours they formed in the atmosphere of Madame Le Paute, finishing them early, supporting the idea of an Jupiter or Saturn, but travelled in just six weeks before the comet interplanetary medium. Bessel BAA COMET SECTION NEWSLETTER 2006 April 5 made the first suggestion of what after his death. There were a lot from 8 AU to 0 AU over 1 My, is now know as the “jet effect” of bright comets during his with rapid changes in inclination. caused by a rotating nucleus. lifetime. All his chums were Secular resonances can have Schiaperelli linked Swift-Tuttle older than he was. Hevelius’ idea enormous effects on comet orbits, with the Perseid meteors, however was that comets were made of despite many orbits being planet this led to the sandbank theory of something else, so didn’t have to crossing, and many end up hitting comets. In 1950 Oort computed obey the same law as planets. the Sun. The observed Halley “original” values of the aphelion Most mid 17th century books Type (HT) comets are mostly distance of a number of comets showed comets moving in straight evolving towards smaller and postulated a cloud at the edge lines. Hooke made a comet perihelion distances, eg Pons- of the Solar System, and Whipple model from wax and iron filings, Gambart. The same applies to 2P/ postulated a solid icy nucleus. suspended in sulphuric acid, and 96P/. Kosai oscillations which grew a tail. He also (where q cos2i is conserved) Giotto encountered Halley in measured coma diameters and tail produce significant variation in 1986 with 100m resolution, Deep lengths using a telescope. Dorffel resonant cases. Mark predicts a Space 1 visited Borrelly in 2001 drew a diagram of the orbit of the new class of NEO/comet orbit, with 50m, Stardust went to comet of 1680. Halley tried to where a direct orbit is flipped into 81P/Wild in 2004 achieving 30m compute an orbit and failed, so he a retrograde one. and noted vaporisation craters, but asked his chums for ideas. no impact craters. Deep Impact Flamstead suggested that the Short period comets (SPC) can saw impact craters on 9P/Tempel, comet was magnetic and was originate by capture from a direct which was a very fragile icy dirt repelled by the Sun. Newton orbit. Predictions suggest around ball. drew the path and calculated the 3000 HT comets, but we don’t see orbit, assuming that the orbit was them, so they must either fade or In answer to a question from Ian a parabola. Halley first disappear. Vice-versa the Ridpath, Don said that there were announced that 1P/ would return predictions give too few JFC, so some similarities between on 3rd January 1696, linking the we need an additional source, eg Borrelly and asteroid Itokawa, but returns of 1606 and 1682. Part of the Kuiper Belt, but probably then the latter had cm sized pebbles. the reason for thinking that still need fading. Resonances in Simon Mitton pointed out comets might return was that mean motion and secular Lyttleton’s work on the passage some comets showed very similar resonances are important and sun- of another star near the Sun and tracks across the sky. Halley also grazing is a common end state. had postulated the formation of thought that comets had hit the The high relative capture comets by accretion. Lyttleton Earth in the past, causing Noah’s probability implies a large number disliked Whipple. David Hughes flood. of dead comets. suggested that the Americans had not been keen to send a spacecraft In answer to a question on how a In answer to a question Mark said to Halley because they believed in comet could get as bright as -7, that secular changes normally the sandbank theory. Peter David said that this was easy if operated over 100,000 years, so Hingley (RAS Librarian) they passed very close to the Sun. there is time for meteor streams to remarked that there was still a lot form. Planetary encounters can of superstition associated with Mark Bailey (Armagh, in then “snip” the streams [possibly comets – he had been rung up by conjunction with David Asher and leading to orphan outbursts such some stockbrokers at the return of V Emel’yanenko) spoke about as that seen in early October 2005 Halley’s comet, asking if it would “Lessons from the Dynamical from Camelopardalus]. Evolution of Halley’s Comet”. In cause a warm winter, and if so th should they sell gas shares! the early 19 century comets were The next speaker was Stephen thought to be interstellar and Lowry (Queen’s University David Hughes (Sheffield those few periodic ones had been Belfast) on “Probing the University) addressed the captured by Jupiter. By the early Properties of Cometary Nuclei”. question of “Edmond Halley: 20th century comets had to be We can image the nucleus Why he became interested in members of the Solar System, directly. HST, Spitzer and ISO comets”. Halley was born in however there was a problem with use a model and subtract the inner north London in 1656 and died in their death rate compared to the coma. There has been direct radar 1742. He was the second greatest age of the Solar System, and a imaging of 2P/, 2004 Q2 and British scientist. The Halley growing number of periodic 2005 JQ5. It is possible to infer picture by Thomas Murray was a comets. Several bright comets properties of the nucleus from “cheap job” by an up and coming gave a boost to theories, eg rare events, eg 1993 F2 20 year old painter, who later Donati, the Great Comet of 1882, (D/Shoemaker-Levy), 1999 S4 became famous. Why did Halley the Great Comet of 1910. By etc. They have been imaging become interested in comets? 1) 1980 the Oort Cloud theory had comets at large solar distances The form of a comet orbit was a developed, with the capture by using ground based CCD, eg big unknown, 2) Kepler’s laws Jupiter of comets with period less comet 2P/Encke over 4 nights to were known, 3) He was an than 200 years, however the get a light curve. With sufficient excellent mathematician, 4) Great excess of Jupiter Family comets observations it is possible to find comets were frequent, 5) All his (JFC) led to the idea of a trans- alpha in the relation N(>r) = cr-α, mates were interested in comets. Neptunian disc. Computer and from what they have alpha is development allowed the 1.6. There is evolution from Halley’s first paper was on investigation of the orbital Kuiper Belt Object (KBO) to planetary orbits. The discovery evolution of Halley’s comet. Centaur to JFC. 2001 OG108 was rate of comets increased during Resonant perturbations can originally classed as Damacloid, his lifetime, and even more so change the perihelion distance but it had an outburst which made BAA COMET SECTION NEWSLETTER 6 THE COMET'S TALE it a comet. It has a rotation period had thought it was just the poor primordial, and was originally of 57 hours, 4% albedo and a seeing. However in July when it much more massive. JFC came diameter of around 10km. No was closer to the Sun it showed a from Centaurs, some of which spectral features were seen. clear tail. This demonstrates that come from the SDO and others you have to observe them when from the Oort cloud. The SD has Dead comet candidates are close to the Earth and Sun, and 105 objects larger than 100km, generally very blue [I may have with good seeing. and 1010 larger than 1km. got this the wrong way round]. Medium sized objects probably There appears to be a rotational Cometary nuclei are often red and look like Phoebe, and the smallest period cut off for comets, dark. There are 500 NEOs with objects look like comets. implying a density of around 0.6 known colours and 80 with g.cm-3, but a few objects imply a albedos. There is an abundance After lunch Mike A’Hearn density of 3. More work is of D types and low albedos in (University of Maryland, USA) needed to populate the statistics. those with Tj < 3. This implies told us about “Deep Impact: The 67P rotates in 12.7 hours. They that 15% of NEOs could be JFC, Experiment”. The impactor came used the VLT to image comet which is more than the 6% that in obliquely at an angle of 20 – Halley in 2003, when it was at 28 dynamicists want, but 8% could 36°. The glitches in the encounter AU, with a magnitude of 28.2, be outer belt asteroids, although animation were due to dust hits; which implies that it can now be the dynamicists need to do more there were four, with the largest imaged through aphelion. They work on this class of object. having a mass of 0.5g, spot on the are starting to observe Long Overall there is a 50/50 chance of predicted size distribution. Period Comets (LPC) beyond 10 a D-type, low albedo asteroid with Imaging was down to boulder AU. 2001 G1 at 10 AU showed a Tj < 3 being a comet. sized objects. There was plenty starlike nucleus with a detached of geology: large smooth surfaces, tail. In answer to a question from craters, old striped terrain, scarps, Mark Bailey, Alan said that the evidence of layers with rough Alan Fitzsimmons (Queen’s size distribution of NEOs and terrain above and below smooth University Belfast) was searching comets followed the same power terrain. The effective radius was for “Comet Candidates Amongst law. David Hughes said that 3.0km, with maximum and the NEO Population”. Why is surface activity often varied from minimum diameters of 7.6 and this important – predictions apparition to apparition, and we 4.9km. The jets haven’t yet been suggest that JFC should evolve don’t know why. associated with surface features. into NEO orbits and we need to The camera was 6mm out of focus test theories of end states. It also The final speaker before lunch on a long focal length instrument, helps to measure the overall was Neil McBride (Open however unlike the HST it was impact risk. There is opportunity University) speaking on “Comets possible to recover good images for remote and in-situ sensing. in the Kuiper Belt”. The first through deconvolution. The KBO was discovered in 1992. colour image showed the comet Dynamical evolution alone can The discovery rate had peaked a was reddish, with the brightest produce JFC from Trans- few years ago. There were areas having an albedo of 4% and Neptunian Objects (TNO) with a several classes: Plutinos, which a factor of two variation. ≥ 2.5 AU. There is a problem had a 3:2 mean motion resonance Outbursts happen all the time [and with Encke type objects, and to with Neptune, Classical which are very small], but are short get such small aphelia needs orbited between about 42 and 47 lived, decaying in typically an perturbations from the terrestrial AU, and a tail of Scattered Disk hour, they recur on particular planets and strong non- Objects (SDO), which ranged parts of the nucleus, which has a gravitational forces. from 44 to 100 AU. Centaurs had rotation period of 40 hours. Observationally 2% of NEOs are semi-major axes less than that of Outbursts go to the NE quadrant active comets, but 6% of NEOs Neptune. There are now over as the ‘top’ surface rotates into could come from JFC. Where are 1000 objects with semi-major sunlight. It has a temperature of they? It may be a question of axes greater than that of Neptune. 365 – 240 K, and is locally in poor discovery due to their inert There are a few with very large solar equilibrium, implying that nature or low albedos, or lack of aphelia, but there is a problem in there is no thermal inertia below identification due to low observing these as they spend about 1cm. This means that the inactivity. Comets generally most of their time at great surface is hottest at noon, when occupy a different space of the e/q distances from the Sun. Some are the Sun is highest in the sky. diagram compared to NEOs, but bigger than Pluto, and there are some high eccentricity objects some with large light curves, for A gravity controlled crater was may be comets. Objects with the example 2004 EL61 is 1500km in created. The ejecta were optically Tisserand invariant Tj more than 3 size and rotates in 4 hours. Many thick and cast shadows. A ray are asteroidal, but what of those are binaries with similar sizes and structure appeared. A small puff less than 3? Images of 2003 KV2, a large separation, and are of material at 3500K was emitted which has Tj = 2.86, showed a probably remnants of three-body very quickly in about 0.5 seconds, tail. They had found a few more captures. Their spectra are similar before the main ejecta came out. objects, eg 2005 JQ5 (Tj = 2.96). to Pluto or Triton. There is a This was about 10 tons of liquid In May when they observed 169P range form neutral to very red silicate. The rest of the material ≡ 2002 EX12 (Tj = 2.89) it was colours, but there may be four was cold – room temperature or nearly stellar, although when broad types. The classical objects less, and amounted to about observed a few days later with are all red. The Centaurs are 10,000 tons. The ejecta were larger aperture and better seeing it either neutral or red. The bluish, as were some of the was completely stellar, so they scattered disc is more or less surface patches, implying ice on
BAA COMET SECTION NEWSLETTER 2006 April 7 the surface and ice crystals in the nucleus, whilst correlated swarms asymmetric emissions. X-rays ejecta. There were large particles, are from fragmentation outside come from charge exchange which consisted of weakly bonded the acceleration zone. between cometary ions smaller particles. The overall downwind. We don’t know what density of the nucleus was 0.4 role tail rays [frequently seen in g.cm-3 and it was as strong as images] play. Rosetta will talcum powder, with a 75% investigate these aspects, and also porosity. Spectra show water, the distant ‘inert’ nucleus. There carbon dioxide, CH-X and is no evidence for a plasma tail in organics after the impact. The Deep Impact data. crater was about 100m across and 20m deep. There is lots of water Max Wallis pointed out that ice below the surface. There is comets have a large hydrogen much work still to be done on the coma, so not all cometary ions are data. heavy.
A comment was made that ice The final speaker was Gerhard isn’t expected on the surface, so Schwehm (ESA/ESTEC, The where do the patches come from. Netherlands) who presented A suggestion was overnight frost. “ESA’s Rosetta Mission to Comet In answer to a question Mike said Churyumov-Gerasimenko”. We that an overhang had been seen on study comets to understand the
81P/Wild despite the talcum like Comet particle tracks in Stardust aerogel history of the solar system. The consistency. Mark Bailey lander is named Philae after an commented that accretion must The more distant material seen at Egyptian obelisk, now in the have occurred at low relative 700 seconds can’t be a jet and garden of the Kingston Lacy velocity. may be a 40cm sized boulder estate in Dorset, which helped to fragmenting, several hundred days decipher hieroglyphs. There are Neither David Bowdley or Paul after ejection from the nucleus. 11 instruments on board Rosetta, Roche (Cardiff University) were The mass distribution is similar to covering imagery (down to 4cm), able to give their presentation on that seen in Halley, ie most of the spectroscopy, mass spectrometer, “Deep Impact on Maui: Scientific mass in a few large particles. He radio, dust, plasma and and Educational Collaboration estimates that about 3000 15 tomography. The lander, which with the Faulkes Telescope”, so micron particles will have been has a mass of 100kg, will anchor Simon Green (OU) spoke on trapped in the aerogel, with 500 itself with harpoons. The target, cometary dust measurements near from the second event. Similar 67P/Churyumov-Gerasimenko is 81P/Wild from Stardust. The about 4km diameter, has a density evidence for small fragmentation -3 primary mission of the spacecraft events has been seen in many of between 0.2 and 1.5 g.cm , an was the sample return and it had comets, eg Halley, Grigg- albedo of 4% and a rotation an imaging camera. There was Skjellerup, Borrelly (Deep Space period of 12.3 hours. The also a dust flux monitor, which 1), West, Hale-Bopp. We should rendezvous is due in May 2014 could detect particles down to 3 be able to get an estimate for the and the mission will run till 2015 microns, but only over a small density of the grains from the after perihelion. The spacecraft is area. A UK sensor had a larger sample return. derived from a area and could detect particles telecommunications satellite as down to 50 microns. There was a Andrew Coates (Mullard Space they are designed for a long life. maximum detection rate at closest Sciences Laboratory, University The solar panels are 32m from tip approach to the comet, followed College London) followed on to tip. Rosetta observed 2002 T7 by a second peak 700 seconds with “Cometary Plasma Tails”. in April after commissioning, and later at a distance of around Comets show some similarities to 9P/Tempel in July. All the 4000km from the nucleus. There Venus, Mars and Pluto. The bow instruments are working well. was a surprising distribution at shock position depends on the closest approach, with clear volatile production rate, with a Gerhard was asked given the low swarms of particles giving jumps density and tensile strength, what -1 factor of 100 variation between -1 in the rate from 0 to 1000 s in a Halley and Grigg-Skjellerup. happens in a 1 m.s impact? He few seconds. At higher Neutrals ionise in sunlight or by thought that the lander would go resolutions the rate jumped from 0 charge exchange. The solar wind in to about 30cm, but that more to 500 in bursts in as little as 1/10 slows down due to cometary studies were needed. I asked how second, equivalent to a distance of output – heavy cometary ions are the microgravity field would 600m. The jets have an angular added to the flow causing affect the lander and orbitter. width of around 5° corresponding deceleration by mass loading. Gerhard said that the field would to a distance of 600m and clearly The magnetic field is frozen into be mapped from the initial orbit give rise to the swarms. The jets the flow. Once ionised, ions and the safest trajectory to the have been mapped back to the move in a cycloidal path and can most interesting site would be nucleus. Not all swarms are be accelerated to 70 keV. Most of chose. The orbit prior to release correlated directly to the jets, and would be at 2km, so the transit -3 the acceleration happens near the jumps in density from 400 m to bow shock. The Ulysses time for the lander would be 0 in 1/10 second imply the spacecraft detected the tail of short. It was suggested that the fragmentation of large grains. comet 1996 B2 (Hyakutake) at 3.8 small asteroid, (2867) Steins, due Anti-correlated swarms are from AU. At comet Borrelly the to be encountered en route might fragmentation events close to the pickup was asymmetric, reflecting be an interesting object itself. BAA COMET SECTION NEWSLETTER 8 THE COMET'S TALE
Professional Tales
Many of the scientific magazines On the lower border is a picture of Bobrovnikoff, Z. Sekanina, F. L. have articles about comets in ghostly empty vessels floating on Whipple, V. P. Konopljova, A. S. them and this regular feature is a calm sea with only black thread. Guliev et al. studied the secular intended to help you find the ones It is only a sketch that is why it is variations of cometary brightness. you've missed. taken as a dream. It is worth They confirmed the reality of the noting that Odo Bishop of brightness fading of short-period First some abstracts from the 37th Bayeaux or later Earl of Kent was comets, they determined the Lunar and Planetary Science a half brother of William and took values of this fading for several meeting; the full papers are a leading part in the Hastings comets and they shown an available on the web. Campaign and conquest of influence of 11-year solar cycle England. Odo a warrior bishop upon secular variations of Paper 1092 - References to was born c. 1033 A.D. and died in cometary brightness. historical comets from 497 A.D. Sicily in 1097 A.D. He probably to 1402 A.D. in English commissioned the famous A paper by Zdenek Sekanina and manuscripts. E. G. Mardon & A. Bayeaux Tapestry for the Paul W. Chodas dealing with the A. Mardon dedication of his new cathedral "Origin of the Marsden and Notre Dame in the city of Kracht groups of sunskirting Paper 1527 - Representations of Bayeaux in 1077 A.D. It is said comets", I. Association with halley’s comet in April 1066 that the tapestry was hung around Comet 96P/Machholz and its A.D. found in the Bayeaux inside the church once a year on a interplanetary complex" has been Tapestry and other special feast day for centuries. published in the Astrophysical contemporary written accounts. Journal Supplement Series, 161, J. A. Greenspon (StarGate In conclusion this is the first p.551-586, December 2005. Research), A. A. Mardon, E. G. pictorial record of a comet. The Mardon (Antarctic Institute of first time that it is mentioned in Maik Meyer provides this Canada) literature outside of the synopsis of the paper and highly Chronicles was in 1476 A.D. So recommends it (all 37 pages!) to Introduction: This Medieval we can date the comet because of everyone interested in the new embroidery - incorrectly called the battle of Hastings. The comet sunskirting comet groups. tapestry is a band of linen - 231 appeared in April 1066 A.D. for feet long and more than 19 inches almost two weeks. By day and by * The tidal stresses experienced wide. A portion of it is missing night. It was very bright. [...] by the sunskirting comets are only including the final portion. It about 0.5% of the stress which is depicts the Norman Conquest of Conclusion: The breadth of experienced by sungrazers England leading up to the Battle separate references to the (Kreutz comets). of Hastings in 1066 A.D. in which appearance of Halley’s Comet in Harold Godwin king of England 1066 A.D. in England indicated * Of the several linkages was killed. that the comets appearance was an presented in recent MPECs the important historical event and ones for the Marsden group It is a remarkable work of art and indicates a serious contemporary comets are the most reliable. The important as a source of mid-11th interest in astronomy. It indicates ones between several Kracht Century history. Legend states that more effort should be group comets are highly uncertain that the Bayeaux Tapestry was directed in the research and and possibly not correct. made by Queen Matilda William recovery of historical references of Normandy with the help of the to astronomical events such as * The link between C/1999 J6 and ladies of his court. It contains 70 comets or as sometimes referred C/2004 V9 is regarded as virtually scenes and various Latin words. to as ‘star.’ Their could be more certain. Scene 31 of the Bayeaux Tapestry historical references to comets states in Latin: "ISTIMIRANT that have long periods that we * The orbital period for the STELLAE" - "Marveling at the have as yet to see appear again in Marsden group is expected to be star." the 21st Century or some time in between 5.5 and 6.0 years. (This the far future. in turn means that it is possible The six men are in the scene that no further (new) members pointing to the comet in the sky Paper 1597 - Some properties of will be found, except ones that with signs of fear. On the border secular variations of brightness were missed in the early times above is a drawing of a comet of some periodic comets. V. S. when SOHO was not operating moving from left to right. The Filonenko due to problems.) We obviously comet appears as a round ball of see the final apparitions of the red with white points and a Introduction: A secular fading of members of both groups. burning rake like object tail being the integrated brightness of sort- drawn from the ball. Scene 32 is period comets was found by S. K. * Fragmentation of C/1999 J6 of King Harold on his throne Vsekhsvyatsky. He interpreted took place most likely about 100 bending towards a man who this as a result of the days prior to perihelion. When appears a soothsayer or an disintegration of cometary nuclei. visible in SOHO in 1999 the interpreter of dreams. This phenomenon confirms youth angular separation of the of short-period comets and their fragments was below the quick evolution. N. T. resolution of the coronagraph. BAA COMET SECTION NEWSLETTER 2006 April 9
silicates, carbonates, ice etc, meteor shower is seen again in the * The lifetime of the fragments is which implies that the early solar future. not expected to be longer than 2 system was well mixed, as these to 5 revolutions, depending on the species all come from different "Jarmo Moilanen (Finland), initial mass. source regions. detected twelve meteors from a compact geocentric radiant at R. * The visual magnitude of C/1999 The Cambridge-Conference A. 164.1 ± 2.0º, Decl. +78.9 ± J6 at its presumed close approach Network (CCNet) 0.5º, on the border of Draco and to Earth in 1999, of maybe 0.009 Camelopardalis, in the evening of AU is derived to be of 19 to 21 CCNet was an electronic network October 5, 2005. The differential mag, explaining why it was not devoted to catastrophism, but mass distribution index was a low detected. The lightcurve can not which included occasional s 1.4 ± 0.2 (+0 to -6 magnitude). be described by usual models. information on comets. Over the The new shower was confirmed last year or so it has become by Esko Lyytinen (2 meteors, * The minimum diameter of increasingly devoted to early period only, located at 25.00 sungrazer which may survive a greenhouse warming scepticism, E; +60.25 N) and Ilkka Yrjölä (4 perihelion passage is estimated to however there have been a few meteors: 26.4 E, +60.9 N) at be about 1 km, with typical sizes comet related items. To nearby locations, and by Sirko for observed ones 16m to 130m! subscribe, contact the moderator Molau in Germany (7 meteors). For sunskirters the diamters are Benny J Peiser at Esko Lyytinen calculated an much smaller, for the bright one
The information in this report is a continuous in 2004. The pattern Horace Tuttle was the first synopsis of material gleaned from in the 2005/6 apparition was a discoverer of 41P/Tuttle- IAU circulars 8620 – 8711, The little different, with most Giacobini-Kresak in 1858, when Astronomer (2005 October – 2006 outbursts concentrated in the he found a faint comet in Leo April) and the Internet. Note that second half. At many recent Minor. Nearly 50 years later, the figures quoted here are outbursts it has reached 13m. It Professor M Giacobini discovered rounded off from their original spends the first half of the year in a 13m object whilst comet published accuracy. Lightcurves Aries, reaching opposition in late hunting, which was observed for a for the brighter comets are from November as it retrogrades on the fortnight. A C D Crommelin observations submitted to The Astronomer and the Director. A full report of the comets seen during the year will be published in the Journal in due course. I have used the convention of designating interesting asteroids by A/Designation [Discoverer] to clearly differentiate them from comets, though this is not the IAU convention.
Information that used to be published in the Observing Supplement can be found on the Section web pages and in the BAA Guide to Observing Comets. Reminders of the observing circumstances of forthcoming comets will however continue to appear in these pages.
Hervé A Faye discovered 4P/Faye in 1843 during a visual search with a small telescope at the Paris Observatory. It reached Observing circumstances for 4P/Faye 5m, though this has never been reached at subsequent returns. It borders of Taurus and Perseus. linked the apparitions in 1928 and is possible that this was a one off The comet is an ideal target for made predictions for future caused by a slight reduction in those equipped with CCDs and it returns, but the comet wasn't perihelion distance from 1.8 to 1.7 should be observed at every recovered and it was given up as AU following a close encounter opportunity. It is well placed this lost. In 1951, Lubor Kresak with Jupiter in 1841. Several year and UK based observers discovered a 10m comet in authors have suggested that the should be able to recover it again 25x100 binoculars whilst absolute magnitude of the comet in July. participating in the Skalnate Pleso is declining rapidly, but it reaches Observatory's program of routine a similar magnitude at all searches for comets. After further favourable apparitions. This observations the comet was return is very similar to the 1991 identified with the lost comet and return, when it reached 10th a better orbit computed. The magnitude. We should be able to comet underwent a series of pick it up in the morning sky in encounters with Jupiter in the July, and it reaches opposition on sixteenth century, which reduced the border of Cetus and Pisces in the perihelion distance from late October. It is at its brightest around 1.5 AU to 1.0 AU. in early November and slowly fades. At the 1973 return, which was similar to the 1907 return, it 29P/Schwassmann-Wachmann underwent a major outburst and is an annual comet that has reached 4m, before fading and outbursts, which in recent years then undergoing a second outburst. Alternate returns are seem to have become more th frequent and were more or less favourable and this, its 10 , is one of them. At the last two returns BAA COMET SECTION NEWSLETTER 2006 April 13 the comet has reached around 8th 52P/Harrington-Abell was magnitude and it could do a little discovered on a plate taken for the Michael Clark of Mount John better this time, although the Palomar Sky Survey by Robert G Observatory, New Zealand CBAT ephemeris suggests that it Harrington and George O Abell. discovered 71P/Clark on a will only reach 11th magnitude. This is the eighth observed return variable star patrol plate in June The comet has not been observed of the comet since its discovery in 1973. At discovery the magnitude visually at the time of writing, but 1955 and it never became brighter reached 13, but alternate returns is expected to be within range than 17th magnitude until 1998. It are unfavourable and it is then 5 soon. It begins May in Gemini was not expected to get brighter magnitudes fainter, though it and continues through Cancer, than 15th magnitude at that return, hasn't been missed. An encounter Leo and Virgo, remaining however it was found in outburst with Jupiter in 1954 put it into its relatively low in the western sky. at 12th magnitude in 1998 July, present orbit, which is such that it It should be at its best in June, which was seven magnitudes can approach quite closely to when it is in Leo. brighter than expected. After the Mars, passing within 0.09 AU in 1978. This is the comet's 7th return since discovery and it could reach 10th magnitude during the northern summer. As might be expected from the discovery, it is best seen from the Southern Hemisphere and will not be visible from the UK.
The comet was recovered at the 2006 return by several observers, including Ernesto Guido, an Italian amateur astronomer. He provides the following details: At the end of November I started the project to try to recover comet 71P. The first attempt was unsuccessful, probably because the comet was fainter than 19 magnitude, which was my limiting magnitude. On 29 December I tried again and this time I found 71P at 7' away from the nominal position roughly at 18.5
Observing circumstances for 41P/Tuttle-Giacobini-Kresak magnitude. On 30 December I was able to obtain a second night outburst it faded, and it is unclear as requested from MPC. 45P/Honda-Mrkos-Pajdusakova how bright it will get this time makes its 11th observed return around. In any case, it is not a Comet 73P/Schwassmann- since discovery in 1948 (it was favourable return and is poorly Wachmann missed in 1959). It has had placed for observation from the Professor Arnold Schwassmann several close encounters with UK. and Artur A Wachmann of Jupiter, the most recent in 1983 which made dramatic changes to ω and Ω. The perihelion distance has steadily decreased and is now the smallest it has been for the last 200 years. It can approach quite closely to the Earth and will do so in 2011 (0.06 AU) and 2017 (0.09 AU). At present the MPC only lists eight approaches closer than 0.06 AU out of 20 passes closer than 0.102 AU, and five of these are by periodic comets. It can also pass close to Venus and does so on June 4th, when it passes at 0.083 AU. It was well observed in 1995/96, when it reached 7th magnitude, but in 2001 it was fading from 9th magnitude. This is not a favourable return for UK observers, but it may be seen from further south during May and June when it is a morning object on its way in to perihelion. Observing circumstances for 71P/Clark for the Southern Hemisphere. These diagrams are made using Richard Fleet’s Graphdark software. BAA COMET SECTION NEWSLETTER 14 THE COMET'S TALE
- Serpens region. Strong activity was reported in 1930 by a lone Japanese observer, but little has been seen since then. It is likely that any future activity would be in the form of a short-lived outburst, confined to years when the comet is at perihelion.
The comet was recovered on 2005 October 22.49 by Carl Hergenrother. The correction to the orbit published in the 2005 comet handbook was delta T -0.43 days. A paper on the 1995 splitting of the comet by Zdenek Sekanina, together with ephemerides for the components at this return was published in the ICQ. IAU circulars have regularly announced the discovery of further fragments, and there are m at least 40 under observation. Hamburg Observatory discovered brightest one is likely to reach 5 , Many are short lived, and their their third periodic comet on thus becoming visible to the brightness variation is highly minor planet patrol plates taken naked eye. The encounter erratic. Component (B), which on 1930 May 2. Initially of magnitude 9.5 it brightened to nearly 6m, thanks to a very close approach to Earth (0.062 AU) on June 1. The initial orbit was a little uncertain and the comet wasn’t found at the next or succeeding apparitions until 1979. The comet passed within 0.9 AU of Jupiter in 1953, and 0.25 AU in 1965. In August 1979, Michael Candy reported the discovery of a comet on a plate taken by J Johnston and M Buhagiar while searching for minor planets; this had the motion expected for 73P/Schwassmann-Wachmann, but with perihelion 34 days later than in a prediction by Brian Marsden. Missed again at the next return, it has been seen at the last three returns. At the 1995 return the comet underwent a major outburst near perihelion, reaching 5m when it was only expected to be 12m. Subsequently circumstances are favourable for had seemed a major fragment, four components were observed, the UK. At closest approach the began to disintegrate at the though calculations by Sekanina fragments will be racing across beginning of April, undergoing a suggested that the fragmentation the sky at around 4.5° a day, brightness surge that briefly made occurred after the outburst. Three strung along an arc of around 12°. it brighter than component A. fragments were recovered in The main fragment (C) is The evolution was then 2001, but only a few visual predicted to pass at 0.079 AU on remarkably similar to 1999 S4, observations were reported as the May 12.38 when it is in forming an elongated coma comet was poorly placed and the Vulpecula. The other fragments without a centre of condensation. absolute magnitude had clearly will follow it, approaching closer faded a little from the previous and will be further north in the Brian Marsden provided a list return. The components have sky. After the encounter they [MPEC 2006-G10, 2006 April 3] now separated in the date of rapidly head south and will be of perihelion times for the first perihelion by roughly a day. difficult to observe a week later. identified fragments in chronological order: The comet's 1930 approach to With the orbit approaching so Earth is currently ninth on the list closely to the Earth, an associated 6.95 C of well-determined cometary meteor shower might be expected, 7.74 Q approaches to our planet. In May and the comet has been linked to 7.88 P the fragments will make another the Tau Herculid shower, though 7.93 B close approach, when the the radiant now lies in the Bootes 8.11 G BAA COMET SECTION NEWSLETTER 2006 April 15
8.14 J A cometary coma was detected 8.20 R around the centaur asteroid 8.24 S (60558) 2000 EC98 on 2005 8.24 K December 30.50. At discovery by 8.28 M Spacewatch in 2000 the object 8.29 H was 21st magnitude, but the 8.30 N development of a coma has 8.35 L caused it to brighten by at least 3 8.51 W magnitudes. Visual reports 8.58 X suggest it could be even brighter, 8.81 Y and Seiichi Yoshida reports it at 8.83 T 14.4, with a 0.5' coma and DC3 in 9.02 U his 0.4m reflector on January 9.08 V 8.78. He suggests that this may be the most distant visual detection of a comet, as the object is 13 AU from the Sun. The object is in a 35 year orbit, and not due to reach perihelion until 2015, when it will be at 5.9 AU.
I suggested that the case seems similar to that of Chiron, which is (2060) 95P/Chiron, so the object should receive a cometary number. Roll on comet Pluto! Spitzer image of 73P taken in early May. The Committee on Small Bodies The image scale is not stated, but may be Nomenclature duly agreed to give around 15’ per frame. the comet P/2000 EC_98 (cf. IAUC 8656, 8660) the same name Visual observations in early as the centaur minor planet (60558), Echeclus (cf. MPC March put the main fragment of Stop press news: a dramatic the comet ('C') at 12th magnitude, 55988), which has been assigned outburst in fragment ‘B’ put it up also the permanent comet number with the brightest of the others to 5th magnitude on May 9, with it ('B') at 14th magnitude. It 174P (MPC 55911). [IAUC 8677, easily visible in 20x80B from 2006 February 22] brightened rapidly, and by early central Cambridge the following April component C had reached 10th magnitude and was easily visible in large binoculars. 'B' was reported in outburst on April 2nd, and subsequent analysis of the photometry by Giovanni Sostero suggests that the outburst began a few days previously. On April 3.95 I observed both components in 20x80B and found that 'B' was noticeably brighter than 'C', with an estimate at around 9th magnitude. Despite a bright moon they were easily visible in large binoculars from sub-urban locations. A second outburst of B was reported in late April.
evening, despite light pollution, 2004 B1 (LINEAR) may get to moonlight and mist turning to low 13th magnitude at its best in May. cloud. It is moving rapidly northwards and enters UK skies at the end of 1997 V9 (SOHO) was a non- April. It moves through Aquila, group comet found by Rainer Hercules, Corona Borealis, so Kracht whilst searching archival becomes steadily better placed for images for Meyer and Marsden viewing. A few observations group members in March. from Southern Hemisphere last October suggest that it might even th 2000 EC98 (174P/Echeclus = be as bright as 11 magnitude, so 60558) it will be worth trying to view it. BAA COMET SECTION NEWSLETTER 16 THE COMET'S TALE
[2005 December 3] that it seems from least-squares cubic likely that the Kracht-group comet reductions (i.e., using 11 or more C/2005 W4 is a return of C/2000 reference stars), in the case of O3 (cf. MPEC 2000-Q09), a C/1999 U2 this is true only for the suggestion made by S. Hoenig. observations shown with note 1 The orbital linkage utilizes just (rather than 2) in column 14. For the C2 observations (those from the remainder it was necessary to July 30.89596 onward in the case make only quadratic reductions, of C/2000 O3); although only the and the observations from 1999 first three C/2005 W4 10 24.70145 onward are observations were obtained with particularly unsatisfactory. Since C2, the residuals of the C3 the orbits below also reasonably observations are not represent the generally inferior C3 systematically displaced. This observations in both 1999 and orbit gives the comet a period of 2005 (i.e., without systematic 5.3 years and perihelion at 0.054 residuals above about 70 arcsec), AU. Jonathan Shanklin it seems likely that the linkage is
discovered the comet in 2000, and in fact correct. Comet 2005 E2 (McNaught) was Bo Zhou made the recovery. discovered by BAA Member Rob SOHO Kreutz group comets McNaught on March 12.75 with Marsden Group SOHO comets 1996 R5, 1997 J6, 1997 O3, 1997 the 0.5m Uppsala Schmidt, during 2005 G2, 2005 W1, 2005 W5, V8, 1998 L10, 1998 T2, 1998 U7, the course of the Siding Spring 2006 E2 and 2006 F3 were 1998 W8, 2005 S12, 2005 S13, Survey. It reached perihelion at discovered with the SOHO 2005 T6, 2005 T7, 2005 T8, 2005 1.52 AU in late February 2006, LASCO coronographs and have T10, 2005 T11, 2005 U2, 2005 when it reached 10th magnitude. It not been observed elsewhere. U3, 2005 U4, 2005 U5, 2005 U6, was never very well placed and They were sungrazing comets of 2005 U7, 2005 U8, 2005 V2, was fainter than expected. It is the Marsden group. 2005 V3, 2005 V4, 2005 V5, now in solar conjunction. 2005 V6, 2005 V7, 2005 V9, Marsden group comet 2005 W1 2005 W6, 2005 W7, 2005 W8, has been linked to 2000 C4. Brian 2005 W10, 2005 W12, 2005 Marsden notes on MPEC 2005- W13, 2005 W14, 2005 W15, W07 [2005 November 18] that it 2005 W16, 2005 W17, 2005 X2, seems probable that this comet is 2005 X3, 2005 X4, 2005 X5, identical with C/2000 C4 (MPEC 2005 X6, 2005 X7, 2005 X9, 2000-C52; alternative direct orbit 2005 Y3, 2005 Y4, 2005 Y5, chosen on IAUC 7832 and MPC 2005 Y6, 2005 Y7, 2005 Y9, 44860), although it is conceivably 2005 Y10, 2006 A4, 2006 A5, identical with C/2000 C3 or 2006 A6, 2006 A7, 2006 B2, C/2000 C7, which appeared 2006 B3, 2006 B5, 2006 B6, 2006 around the same time (and, if they C1, 2006 C2, 2006 C3, 2006 D2, still exist, are also presumably 2006 D3 and 2006 D4 were about to return). The linked orbit discovered with the SOHO has a period of 5.78 years, with LASCO coronographs and have aphelion beyond the orbit of not been observed elsewhere.
Jupiter. They were sungrazing comets of Sebastian Hoenig has predicted the Kreutz group and were not that 2002 R5 (SOHO) may return Brian Marsden notes on MPEC expected to survive perihelion. in August. If his prediction holds, 2005-X14 [2005 December 3] that Some of these comets show no the object could become visible to comet C/2005 W5 has not been tail at all and it is possible that Southern Hemisphere observers satisfactorily linked to a Marsden- some supposed observations of prior to perihelion, but is unlikely group candidate at its previous Vulcan were actually tiny Kreutz to be brighter than 12th magnitude. perihelion passage, although group comets. There are now potential fits to the various 1999 over 1140 SOHO comets, of Meyer Group SOHO comets members seem preferable to those which some 920 are members of 1996 N3, 1997 X7, 1998 G9, involving the comets of Feb. 2000 the Kreutz group. 2005 T9, 2005 W9, 2005 W11, (cf. MPEC 2005-W07). He 2005 Y8 and 2006 B4 were further notes on MPEC 2005-Y27 2005 V8 (SOHO) was a non- discovered with the SOHO [2005 December 23] Further to group comet discovered by Hua LASCO coronographs and have the note about C/2005 W5 at the Su in C2 images on November 9. not been observed elsewhere. end of MPEC 2005-X14 and its Brian Marsden notes on MPEC They were sungrazing comets of possible linkage to one of the 2005-Y07 [2005 December 19] the Meyer group. Marsden-group comets of 1999, Alternate orbit solutions are Z. Sekanina and P. Chodas, and possible for the non-group comets Kracht Group SOHO comet also R. Kracht, have suggested C/2005 V8 and C/2005 Y1. The 2005 W4 was discovered with the that a fit to C/1999 U2 seems orbit of C/2005 V8 is possibly SOHO LASCO coronographs and most likely. The linkage, giving a similar to that of C/2005 H7. has not been observed elsewhere. period of 6.10 years, is from the It was a sungrazing comet of the C2 observations. It should be 2005 X1 (Beshore) Edward Kracht group. Brian Marsden noted that, although all the Beshore discovered a 20th comments on MPEC 2005-X14 observations of C/2005 W5 are magnitude comet in the course of BAA COMET SECTION NEWSLETTER 2006 April 17 the Catalina Sky Survey on December 7.41. It has passed perihelion, which was at 2.9 AU in early July 2005. It will fade.
2005 XA54 (P/LONEOS-Hill) On January 6.41 BAA Member Rik Hill found an obvious comet on Catalina Sky Survey images. Tim Spahr has identified this with an asteroid discovered by LONEOS on December 4.38 and observed on two nights. The comet has a period of 15 years and reaches perihelion in early March at 1.8 AU. It could brighten to 16th magnitude in February and March, though it is an intrinsically faint object.
2005 Y1 (SOHO) was a non- group comet discovered by Steve of 2006, but is then heading Farmer in C2 images on towards high southern declination. December 17. Brian Marsden notes on MPEC 2005-Y07 [2005 2005 YQ127 (P/LINEAR) was December 19] Alternate orbit originally announced as an solutions are possible for the non- unusual asteroid, of 18th group comets C/2005 V8 and magnitude, discovered by C/2005 Y1. The orbit for C/2005 LINEAR on December 28, which Y1 is heavily weighted toward the had an orbit typical of Jupiter C2 data, which for the most part family comets. It was at are mutually unusually consistent, perihelion at 1.9 AU in early with the comet roughly of mag 7- November 2005 and had a period 8; the comet was much harder to of 8 years. [MPEC 2006-A07, detect in C3, and these reductions 2006 January 2, 5-day orbit]. It were unusually inconsistent. If can approach within 0.3 AU of this orbit is at all meaningful, a Jupiter. As an asteroid it was second entry into the C2 field estimated to be around 6km in Michael Mattiazzo imaged the should occur, although the phase diameter. Further observations comet on January 7 and estimated angle would be very much larger showed cometary characteristics. the magnitude as 10.5 in his 20cm and the magnitude obviously The latest orbit shows that reflector. It seems to be uncertain. perihelion was at 1.9 AU in early brightening quite rapidly as November 2005, with a period of Michael estimated it as 7.9 in 2005 Y2 (McNaught) Rob 7.6 years. 25x100B on January 23.5, with a McNaught discovered another 3' DC5 coma. I was able to comet with the 0.5-m Uppsala 2006 A1 (Pojmanski) Grzegorz observe the comet on Feb 8.05 Schmidt during the Siding Spring Pojmanski, of Warsaw University from on board the Fishery Survey. This one was found on Astronomical Observatory, Protection Vessel MV Sigma at December 30.46, and was 19th discovered a comet on All Sky 54S 39W with 10x50B and made magnitude at discovery. The latest Automated Survey images taken it 6.1. For the next three weeks I orbit confirms early suggestions with a 180mm focal length f/2.8 was at Bird Island, a notoriously that it is a periodic comet, with telephoto lens (+ V filter) at Las cloudy location, but on February perihelion at 3.4 AU in late Campanas. The object was placed 17/18 the skies remained clear December 2004 and a period of on the NEOCP and has been and I estimated the comet at 5.6 in 16 years. confirmed as a comet. Kazimieras 10x50B, DC8 on February 18.21. Cernis also reported an object in Observations received in late 2005 YW [LINEAR] This SWAN imagery, and this has the February put the comet at around unusual asteroid, of 20th same motion as the new comet. 5.5. Once in view from the UK, magnitude, was discovered by The comet is at perihelion at 0.6 observers reported a 5 degree ion LINEAR with the 1.0-m reflector AU in late February. It will tail in early March. By early April on December 21st. Currently 4 initially remain a southern it had faded to around 8.5. AU from the Sun, it reaches hemisphere object, but should perihelion at 2 AU in December become visible from the UK in Brian Marsden notes on MPEC 2006 and has a period of over late February, as a binocular 2006-E43 [2006 March 11] that 1000 years. At aphelion it is 190 object in the morning sky, when it the "original" and "future" AU from the Sun. [MPEC 2005- could be 6th magnitude. It will barycentric values of 1/a are Y43, 2005 December 27, 6-day fade rapidly during March as the +0.000798 and +0.000800 (+/- orbit]. It is classed as a scattered distance from Sun and Earth 0.000011) AU^-1, respectively. disc object or cubewano and has a increases. The "original" value suggests that diameter of around 15 km. It will this is not a "new" comet. reach magnitude 17.5 at the end BAA COMET SECTION NEWSLETTER 18 THE COMET'S TALE
2006 A2 (Catalina) The Catalina approach to around 0.4 AU of Sky Survey discovered another Jupiter. This type of orbit is A/2006 DW62 [LONEOS] This faint comet, of 19th magnitude, typical of Jupiter family comets. Amor asteroid, of 19th magnitude, on January 21.19. It is a distant The object is estimated at around was discovered by LONEOS with object, past perihelion and will 200m in diameter. the 0.59m Schmidt on February fade. Given the discovery date it 26.28. [MPEC 2006-D59, 2006 should properly have been comet A/2006 BV7 [Steward] This February 27] It has a period of 5.9 2006 B1. unusual asteroid, of 21st years, with perihelion at 1.17 AU. magnitude, was discovered from Its orbit is typical of a Jupiter 2006 A3 (175P/Hergenrother) the Steward Observatory with the family comet, and it can pass Comet 2000 C1 (Hergenrother) 0.9m reflector on January 22.39. within 0.1 AU of the giant planet. was recovered by the Mt Lemon It has a period of 7.0 years and It is estimated at around 400m in Survey. The comet will remain at perihelion was at 1.69 AU in late diameter. around 20th magnitude for the December 2005. [MPEC 2006- next six months. The Committee B59, 2006 January 24, 3-day 2006 E1 (McNaught) Rob on Small Bodies Nomenclature orbit]. In the current orbit it can McNaught discovered another has announced that P/2000 C1 = approach to around 0.3 AU of comet during the course of the P/2006 A3 (Hergenrother) has Jupiter. This type of orbit is Siding Spring Survey on March been assigned the number 175P typical of Jupiter family comets. 11.74. The object is 18th (cf. IAUC 8664). [IAUC 8677, The object is estimated at around magnitude and reaches perihelion 2006 February 22] 800m in diameter. at 6.1 AU at the end of the year.
A/2006 AQ [Mauna Kea] This A/2006 BZ8 [Catalina] This A/2006 ED1 [Catalina] This Amor asteroid, of 20th magnitude, unusual asteroid, of 19th unusual asteroid, of 20th was discovered from Mauna Kea magnitude, was discovered by the magnitude, was discovered by the with the 2.24m reflector on Catalina Sky Survey with the Catalina Sky Survey with the January 2.23. It has a period of 0.68m Schmidt on January 23.43. 0.68m Schmidt on March 4.48. 6.3 years and perihelion is at 1.18 The orbit is retrograde and current [MPEC 2006-E25, 2006 March 6] AU in early February 2006. solutions give a period of 30 years It has a period of 5.4 years, with [MPEC 2006-A16, 2006 January with perihelion at 1.90 AU in perihelion at 1.41 AU. Its orbit is 5, 3-day orbit]. In the current orbit 2006 July. Gareth Williams notes: typical of a Jupiter family comet, it can approach to around 0.4 AU Observers with access to large and it can pass within 0.4 AU of of Jupiter. This type of orbit is telescopes are encouraged to the giant planet. It is estimated at typical of Jupiter family comets. search for cometary activity in around 1km in diameter. The object is estimated at around this object. Parabolic and near- 2km in diameter. parabolic solutions are still A/2006 EX52 [Catalina] This possible. [MPEC 2006-B67, 2006 unusual asteroid, of 20th A/2006 AL8 [Siding Spring] January 27, 4-day orbit]. The magnitude, was discovered by the This Apollo asteroid, of 20th object is estimated at around 9km Catalina Sky Survey with the magnitude, was discovered during in diameter. 0.68m Schmidt on March 5.26. the Siding Spring Survey with the The orbit is still rather uncertain, 0.5m Uppsala Schmidt on January 2006 CK10 (Catalina) but it is retrograde and current 8.70. It has a period of 6.7 years Announced as an unusual solutions give a period of around and perihelion was at 0.38 AU in asteroid, of 19th magnitude, it 255 years with perihelion at 2.57 mid November 2005, although the was discovered by the Catalina AU later this year. [MPEC 2006- orbit is still rather uncertain. Sky Survey with the 0.68m E36, 2006 March 9, 18-day orbit]. [MPEC 2006-A58, 2006 January Schmidt on February 4.43. The Somewhat surprisingly it is being 10, 2-day orbit]. The object is preliminary orbit was retrograde classed as a plutino, with a 3:2 estimated at around 1km in with an inclination of 144 degrees resonance with Neptune. It is diameter. and a period of 150 years. [MPEC estimated at 9km in diameter. 2006-C44, 2006 February 8, 4- 2006 B1 (McNaught) Rob day orbit]. Rather as expected 2006 F1 (P/Kowalski) R McNaught has discovered another further observations showed the Kowalski discovered an 18th comet, during the course of the object to have cometary magnitude comet on March 21.49 Siding Spring Survey. This one characteristics and it was given a during the course of the Mt was found on January 27.62 and cometary designation. The orbit is Lemon survey with the 1.5-m was 18th magnitude. It was at retrograde with an inclination of reflector. The initial orbit perihelion in November 2005 at 144 degrees and current solutions suggested that it would reach 3.0 AU and will not brighten give perihelion at 1.75 AU in perihelion at 1.9 AU in 2007 May, significantly. 2006 July. The orbit is parabolic. when it might reach 13th It will be near solar conjunction magnitude. Further observations A/2006 BO6 [Mt Lemon] This when at perihelion. however show that it is in a Apollo asteroid, of 20th periodic orbit [as first suggested magnitude, was discovered by the 2006 D1 (P/Hill) BAA Member by Hirohisa Sato], period 10 Mt Lemon Survey with the 1.5m Rik Hill has discovered another years, with perihelion at 4.1 AU reflector on January 22.11. It has comet during the course of the in February 2008. The comet a period of 5.6 years and Catalina Sky Survey. It is a faint appears to have had a recent close perihelion was at 0.98 AU in late 20th magnitude object in a encounter with Jupiter. December 2005. [MPEC 2006- periodic orbit of 13 years and will B55, 2006 January 24, 2-day fade as it is past perihelion at 1.89 2006 F2 (Christensen) E orbit]. In the current orbit it can AU. Christensen discovered a 20th BAA COMET SECTION NEWSLETTER 2006 April 19 magnitude comet on March 23.33 magnitude and is near perihelion at 200 AU and can approach during the course of the Mt at 2.3 AU. It is in a short period within 0.6 AU of Saturn. It is Lemon survey with the 1.5-m orbit, with period of 6.6 years. currently classed as a scattered reflector. It is near perihelion at disk object or cubewano and has 4.3 AU and has an orbital period A/2006 HA6 [Siding Spring] an estimated diameter of 18km. of 45 years. This unusual asteroid, of 19th magnitude, was discovered during A/2006 HY51 [LINEAR] 2006 F4 (P/Spacewatch) A 20th the Siding Spring Survey with the This Apollo asteroid, of 18th mag comet has been found on 0.5m Uppsala Schmidt on April magnitude, was discovered by Spacewatch images taken on 20.58. It has a period of 5.5 years LINEAR on April 26.35. [MPEC March 26.36 with the 0.9-m and perihelion was at 1.20 AU in 2006-H57, 2006 April 28] It has a reflector by R S McMillan and M early March. [MPEC 2006-H24, period of 4 years and perihelion is T Read. It is near perihelion at 2006 April 21, 1-day orbit]. The at 0.08 AU in early July. It can 2.36 AU and has a period of object can approach to within 0.2 approach within 0.09 AU of around 7 years. AU of Jupiter and 0.22 AU of the Earth, but with aphelion at 5.0 AU Earth. It is estimated at 600m can only approach within 0.9 AU 2006 G1 (P/McNaught) Rob diameter. of Jupiter. It is estimated at 2km McNaught discovered another diameter. comet, during the course of the A/2006 HR30 [Siding Spring] Siding Spring Survey, on April This Amor asteroid, of 19th A/2006 HZ51 [Catalina] 5.70. The object is 18th magnitude, was discovered during This Amor asteroid, of 20th magnitude and reaches perihelion the Siding Spring Survey with the magnitude, was discovered by the at 2.6 AU in August. It has a 0.5m Uppsala Schmidt on April Catalina Sky Survey on April period of around 11 years. 20.78. It has a period of 22 years 27.16. [MPEC 2006-H58, 2006 and perihelion is at 1.23 AU in April 28] Further observations A/2006 GZ2 [Steward] This early January 2007. [MPEC 2006- show that it is rather less unusual asteroid, of 20th H40, 2006 April 26, 9-month interesting, with a period of 3 magnitude, was discovered from orbit]. The object could reach years, although it is a PHA the Steward Observatory with the 14th magnitude when at approaching within 0.06 AU of 0.9m reflector on April 7.18. It is perihelion. It can approach to Earth. in a retrograde orbit with a period within 0.6 AU of Jupiter and a of 60 years and perihelion is at 2.9 similar distance from the Earth. For the latest information on AU at the end of October. [MPEC discoveries and the brightness of 2006-G38, 2006 April 10, 2-day A/2006 HW51 [Siding Spring] comets see the Section www orbit]. It is estimated at around This unusual asteroid, of 18th page: http://www.ast.cam.ac.uk/~jds or 7km in diameter. magnitude, was discovered during the CBAT headlines page at the Siding Spring Survey with the http://cfa- 2006 H1 (P/McNaught) 0.5m Uppsala Schmidt on April www.harvard.edu/cfa/ps/Headlines.html Rob McNaught discovered 23.49. [MPEC 2006-H56, 2006 another comet, during the course April 28] It has a period of 1000 of the Siding Spring Survey, on years and perihelion is at 2.3 AU April 29.79. The object is 18th in late September. It has aphelion Comet Section CCD meeting (Part II) 2005 May 14
Part 1 appeared in the last issue, different way by making a which is available as a pdf on the synthetic coma using a 1/r law for Section web page. the variation in brightness with distance from the coma centre. Nick James introduced Giovanni The 1/r law is what would be Sostero. He noted that Giovanni expected for an ideal coma made was one of the most active comet up of dust. The final image is the imagers in Europe and that he was difference between the original also active in cometary image and this synthetic image photometry. Giovanni started by and shows variations from the introducing some image The first algorithm was called theoretical dust-only coma. processing algorithms that had azimuthal median subtraction. been developed for the This creates a map of pixel Giovanni also mentioned the enhancement of faint cometary intensity across the coma by using Larson-Sekanina method which details. He said that the CARA the median value of pixels in a emphasizes radial detail. He said group (Cometary Archive for series of concentric circles centred that it was interesting to compare Amateur Astronomers) included a on the false nucleus. The median these three methods. If a feature team who were very skilled in image is then subtracted from the was visible using all three then it developing tools for the popular real image to give a map of the was likely to be real but if it was Astroart package and that they coma which shows brightness only visible in one it was probably had taken two algorithms used by differences. This map makes an artifact. Giovanni illustrated professionals and made them subtle photometric details this by showing some images of more accessible to amateur apparent in the final image. The C/2004 Q1 (Tucker) processed in observers. second algorithm was the radial each of the three ways. These weighted method. This works in a showed considerable detail which BAA COMET SECTION NEWSLETTER 20 THE COMET'S TALE was not visible in the original When put together the is concerned. Giovanni said that images but which was consistent mathematical algorithms and the only by using narrowband filters between methods. These methods optical filters were a very can you be sure to get consistent really only work on bright comets powerful tool. Giovanni showed results. and it is very difficult to enhance images of the inner part of the structure if the image SNR is coma of C/2004 Q2 (Machholz) Giovanni showed some examples small. taken in January 2005. The CN of work with 9P/Tempel. This emission line filter shows comet has a very low level of gas Giovanni now discussed the use structure in the central contamination and so the results of optical filters. He commented condensation whilst the dust measured with broadband filters, that the comet spectrum shown by continuum filters show a fan no filters and narrowband filters Mark Kidger earlier in the opening towards the Sun. were similar. One of the problems meeting was one of a quiet comet with 9P was that it shows a very where most of the light was The next part of the talk dealt steep change in AFRho with reflected solar continuum. with photometry. Giovanni aperture size which is unusual. In Frequently comets, particularly described how he had seen a rapid theory, assuming a canonical the brighter ones, were strongly evolution in this aspect of steady-state coma model, the contaminated by emission lines cometary astronomy and that what coma should have the same from ionised gasses. In these was needed for consistency was a AFRho no matter what cases the light from the comet is procedure that amateur observers photometric aperture was used. In made up of broadband scattered could follow. Giovanni said that the case of 9P the different results sunlight from dust and he mostly agreed with Mark must mean that the model is narrowband emission from Kidger but that there were a few wrong. Professionals think that various molecular species in the areas where they had differences, there may be some seasonal coma and tail. Depending on the in particular he thought that effects at work here. Some parts comet these two contributors optical filters were essential. He of nucleus are more active at could be equal or one could showed a spectrum of C/1995 O1 certain distances from sun and at dominate the other. Giovanni (Hale-Bopp) to illustrate this. He certain phase angles. showed the spectrum of C/1996 agreed that there were many B2 (Hyakutake) and Very strong instances where comets had no In conclusion Giovanni said that emission lines could be seen, strong emission lines but that it the CARA photometry is particularly the C2 Swan bands was impossible to know for sure comparable to professional results around 513 nm and strong CN unless you had a spectrum and to within 10-15% and that they emission in the blue). These these were hard to come by. To were good enough to have been emission lines could lead to have a general method that will published in some papers in the incorrect photometry if broadband work properly in all cases it is last few years. unfiltered detectors were used. necessary to use filters. Giovanni also pointed out that the spectral After Giovanni's talk there was an The CARA group had considered sensitivity profile of CCDs varies open forum discussion of the whether it would be possible to considerably and so this would various issues that had been use standard photometric filters affect unfiltered estimates. As far raised. Denis Buczynski asked (e.g. Johnson). They had as CARA are concerned there is “Which method should the BAA concluded that they were better no shortcut and so filters must be Comet section adopt?” Giovanni than nothing but that they were used. described the selection of one still too wide in many cases. For method or other as a "lifestyle this reason professionals use The other problem is that there is choice". The Spanish method may narrowband interference filters no convincing definition of what work 90% of the time but what but these are usually too defines a comet's magnitude! about the 10% of comets where expensive for amateurs. The What do we measure given that the observations were CARA group has selected some the coma gradually merges with contaminated by gas? The Italian filters which are very close to the the sky? The Spanish group use a method was more complex but is professional ones but which are 10 arcsecond aperture and larger did work on all comets. easily available from companies multiples of this. CARA does such as Edmund Optics. The cost something similar but their Mark Kidger argued that that is then much more reasonable (a aperture is defined in terms of most comets did not suffer from 25 mm diameter filter costs physical size at the comet and significant gas contamination. around $90). CARA have used they have decided to fix a Giovanni had shown the bright these filters to image CN (at reference window of 100,000 km ones near to perihelion and Mark + 390 nm), C3 (430 nm) and CO . or smaller. The first test was on agreed that in these cases filters They have also selected filters to C/2000 WM1 (LINEAR) in 2001 were necessary but for the vast isolate bands where there are no November. This was a comet with majority of faint comets the emission lines since this allows us some gas contamination and this Spanish method was effective and to study the dust, unpolluted by meant that the AFRho calculated much simpler for the observer. gas emission. These filters have a using different colour filters Buczynski asked whether very narrow bandpass of only showed different results. Giovanni observed faint comets 10 nm (FWHM) and so are only Unfiltered photometry would far from perihelion with the same practical for bright comets. With have definitely been affected by filters? In reply Giovanni said that fainter comets, such as the gas emission in this case, CARA did not use narrowband 9P/Tempel, exposure times of an without appropriate filters the filters below around magnitude hour or more are necessary. measurements do not have a real 11.5 since exposure times would physical meaning as far as AFRho be too long. In these cases they BAA COMET SECTION NEWSLETTER 2006 April 21 used a broadband R or I filter. any cometary spectroscopy now of a comet on a tapestry! The Mark commented that, for a you wouldn't know how strong earliest Babylonian records are of periodic comet, 3AU out, it was a the gas contribution was. He was Comet 1P/Halley and this comet pretty safe bet that it would not hoping to see more spectroscopy is again recorded in woodcuts have significant emission line from amateurs in the future so that made at its return in AD66. The activity. In conclusion Giovanni the applicability of various most famous Halley record is, of and Mark agreed that the Spanish methods could be checked. course, the Bayeux tapestry method was appropriate for most although it wasn’t a particularly faint comets which were far from Mark pointed out some problems realistic portrayal. Sun although Giovanni did with the Italian method for comets question whether this was observed over a large range of appropriate faint comets such as geocentric distances. He cited an 9P/Tempel. example where the range of geocentric distance was a factor of 10. Since CARA were using a fixed physical aperture size this would change by factor of 10 between the furthest and closest observations, say from 20 to 200 arcsec. This would cause big
problems if the sky background was bright. Usually a fixed In the middle ages comets were angular aperture was better since, considered to be omens of doom if the comet obeys the rules, the but by the 15th century people It was clear that 9P/Tempel was AFRho is independent of were getting a better idea of what rather unusual and Giovanni aperture. He acknowledged that they were and had rediscovered wondered why the Spanish 9P did not obey these rules! what the ancient Chinese had measurements of AFRho were 3-4 Giovanni said that he did not find known that comets tails point times bigger than the problem with 3 arcmin aperture away from the Sun. The 17th and measurements made by other since their CCDs generally had a 18th centuries saw the production groups. Mark said that, since in 10-15 arcmin field of view. Of of magnificent star maps and the this case AFRho was strongly course they needed a very major advances of Halley and aperture dependent, they were accurate sky background Newton allowed much more affected by the small aperture correction in these cases. Mark accurate predictions of comet's size. The Spanish AFRho values responded by stating that he didn't orbits. Hevelius recorded many computed for larger apertures think that it would be possible to comets and he would frequently were more consistent with other get a good sky subtraction at this record multiple nuclei. Today we data. Responding Giovanni said aperture. Giovanni said that, in know that most comets do not that he was not convinced since these cases, they could reduce have multiple nuclei but Jonathan he had made measurements with there aperture down to 25,000 km suggested that visual observers the same 10 arcsec aperture and for instance. Giovanni further should use higher magnificiations obtained an AFRho of 250 cm pointed out that the fixed angular to get early indications of any whereas the Spanish result was aperture sampled different parts of breakups that do occur. 750 cm. Something was wrong. the coma depending on geocentric After some discussion both agreed distance whereas CARA were The 18th and 19th centuries that 9P was a comet with unusual always observing the same produced a number of particularly behaviour. volume at comet. To counter this spectacular comets. One iconic Mark said that the Spanish image was made in 1744 and Nick James asked whether anyone observers now provide results in shows the multiple tails of Comet using Spanish method used an R multiple apertures so that he can de Cheseaux rising above the broadband filter. Mark said that interpolate any aperture horizon. These days we think that some in the Spanish group were dimension that he wants. these may have been synchrones and he recommended this for the in the dust tail. Another BAA since it did at least eliminate To conclude Giovanni said that it spectacular comet was Comet some observational variability. was not important what he or Donati in 1858. Shanklin showed Mark said about their respective a picture of this comet with the Karen Holland asked Mark methods. In the next few years it old Northumberland dome in the Kidger whether it would be would become clear which foreground and compared it to a possible to work out the method was most accepted by the picture of Hale-Bopp with the transformation coefficients of number of third parties who used modern dome. The Earth passed various unfiltered CCDs in the the data. through the tail of Donati and way that Richard Miles had perspective gave rise to great already done with some Starlight The next speaker was Jonathan spreading rays in the sky which Express cameras. In most cases Shanklin who was going to talk must have been particularly they had a response about his historical perspectives spectacular. Shanklin presented a approximating R band in any on comet observation. Jonathan series of woodcuts and copper case. Mark said you could do this said that some of the oldest comet plates which showing parabolic if the spectrum was purely observations were Chinese structure, rays and spines in the reflective but this method could recordings made on silk. This inner coma of Donati. These were not cope with narrowband gas medium was no longer popular very similar to the features visible emission. Since there is hardly but he had once received a record in Hale-Bopp under high power. BAA COMET SECTION NEWSLETTER 22 THE COMET'S TALE
Jonathan moved on to discuss the days before he moved to the In modern times of course there prospects for Deep Impact and professional world, and John was George Alcock. Denis speculated on the effect that the Mellish both of whom used 5-inch showed a picture of a young impact would have. The refractors. Another common Alcock using his 5-inch Zeiss observational circumstances from feature, as Denis noted, was that binoculars. These binoculars were the UK were poor for the July 4 comet discoverers needed to wear now in the safe possession of impact. On the south coast the a substantial hat in those days. Glyn Marsh. One of George’s comet would be 15° up at the end contemporaries, Roy Panther, of nautical twilight and so there Denis pointed out that these made his discovery on Christmas was a chance of seeing it if it discoverers had to be hardy folk. day, 1980 after many years of brightened dramatically. At the Lewis Swift observed from a searching. Roy had built his own latitude of Cambridge it was only rooftop on top of a cider mill. He telescope and was a modest man 10° up at end of nautical twilight left the telescope tube on the roof so he didn't make much of a fuss and further north it was even but carried the lenses up and about the discovery. He has worse. In 1983 the comet had down a 100ft ladder! Other carried on searching to the present reached 10th magnitude and in discoverers roped in assistants to day with no further discoveries. 1994 it behaved in a very similar help with the work. The Reverend way but since it came a little Joe Metcalf involved other Denis concluded the talk by closer it reached 9th magnitude. members of his family in his showing pictures of Albert Jones Extrapolation of recent comet searching and his daughter and Bill Bradfield. Albert has observations suggested that it once wrote that her “brother didn't made a remarkable number of wouldn't get brighter than 10th look forward to the long winter variable star observations but he magnitude this year unless nights when he had to guide also discovered two comets, one something dramatic happened. father's telescope for hours”. The at beginning of his observing The impact was due when the son was never credited with any career and one near the end. Bill comet was near perihelion and of the discoveries! Bradfield built his own reflecting about 1 au from the Earth. comet seeker, designed Jonathan thought it unlikely that It is worth remembering that specifically for his own height the impact would increase the comets discovered around that and made of bits found in scrap active area by more than a factor time were usually brighter than yards or bought in DIY stores. of two so he expected that the best magnitude 8-9 but they must have Despite appearances this was a we could hope for was an increase been very difficult to find given comet discovery machine and his to magnitude 9 or possibly 8. If that the instruments had such dedication has led to a large this were the case it would be a narrow fields of view. Discovery number of discoveries. very difficult observation from the became more efficient as UK given the low elevation. photography was developed. Nick James thanked Denis for his Barnard used the 10-inch Bruce talk and brought the meeting to a photographic telescope at Lick for close rather later than expected. Milky Way work and made the He thanked all of the speakers and first photographic discovery of the audience for the lively open comet. Photography then became forum session and said that he dominant and Max Wolf at hoped that BAA observers would Heidelburg found several comets start to make serious cometary during his photographic asteroid photometry observations in the survey. near future.
Nearer home, William Denning, Nick James The final talk was by Denis the greatest English amateur Buczynski on "discoveries, tools discoverer before Alcock used a [Special thanks to Nick for of the trade". Denis said this was 10-inch, f/8 alt-azimuth transcribing the talks from his to be a light talk since most of the Newtonian for his discoveries. recording of the meeting] meeting had been rather heavy! One of Denis’ favourite discovery He was going to talk about groups was the one based at various famous comet observers Skalnate Pleso where a and the instruments they have programme had been set up used. Discoverers in the 18th and during the 40s and 50s to visually 19th centuries used instruments discover comets using large that would not be considered binoculars. They had a team suitable today. Denis showed a approach and each observer picture of Pons’ brass short-focus would spend a 90 minutes shift searching the sky. The team found refractor on an alt-az mount. He had used this to discover 37 18 comets and the most successful comets from France. William individual observer was Ludmila The Comet's Tale is produced by Tempel also used a refractor on a Pajdusakova who later went on to Jonathan Shanklin, with thanks to strange alt-az mount that allowed a professional career and became the British Antarctic Survey and him to adjust the height of president of the Czech the Institute of Astronomy, telescope. Other famous visual astronomical society? Cambridge for the use of comet observers were Edward computing facilities. E&OE. Emmerson Barnard, in his early
BAA COMET SECTION NEWSLETTER