THE COMET’S TALE

Newsletter of the Comet Section of the British Astronomical Association

Volume 5, No 1 (Issue 9), 1998 May

A May Day in February!

Comet Section Meeting, Institute of Astronomy, Cambridge, 1998 February 14

The day started early for me, or attention and there were displays to correct Guide Star magnitudes perhaps I should say the previous of the latest comet light curves in the same field. If you haven’t day finished late as I was up till and photographs of comet Hale- got access to this catalogue then nearly 3am. This wasn’t because Bopp taken by Michael Hendrie you can always give a field sketch the sky was clear or a Valentine’s and Glynn Marsh. showing the stars you have used Ball, but because I’d been reffing in the magnitude estimate and I an ice hockey match at The formal session started after will make the reduction. From Peterborough! Despite this I was lunch, and I opened the talks with these magnitude estimates I can at the IOA to welcome the first some comments on visual build up a light curve which arrivals and to get things set up observation. Detailed instructions shows the variation in activity for the day, which was more are given in the Section guide, so between different comets. Hale- reminiscent of May than here I concentrated on what is Bopp has demonstrated that February. The University now done with the observations and comets can stray up to a offers an undergraduate why it is important to be accurate magnitude from the mean curve, astronomy course and lectures are and objective when making them. and if such a part of the light given in the Hoyle seminar room The first task in observing a curve is all that is used for the from 10:00 till 12:15, so the comet is finding it – not a analysis, erroneous magnitude pattern of the event has changed a problem with the likes of Hale- parameters will be determined. little from previous years, Bopp and Hyakutake, but a far Measurements of the coma allowing a little more time for harder task for the typical periodic diameter tell me something about leisurely chat between the 50 or comet. The ephemerides in The your observing conditions and so participants. Comet’s Tale and on the Section also something about the physical web page give an indication when size of the coma. Recent comets After welcoming refreshments, it is possible to observe a given show a wide range of variation, members were able to tour the comet. They also give the with some having a diameter than Royal Greenwich Observatory, position of the comet in B1950 appears to vary little with solar perhaps for the last time, guided co-ordinates (as used by the distance. The degree of by Margaret Penston. Members AAVSO atlas) and J2000 (as used condensation can vary of the Cambridge University by the Millennium atlas): if you dramatically and Astronomical Society (CUAS) use the wrong set you won’t see 73P/Schwassmann-Wachmann 3 demonstrated the Northumberland the comet! You can use PC was almost star like when it and Thorrowgood refractors and planetarium programs such as outburst, but gradually became the Schmidt telescope of the Megastar or Guide to produce more diffuse. University Observatories. The accurate finder charts, however Northumberland was trained on when you know exactly where to Continued on page 3 Venus, but unfortunately the look it is important not to Thorrowgood dome had suffered convince yourself that you can see mechanical failure and the something that isn’t there. I Contents telescope could not be pointed at sometimes wonder if some of the the Sun. After the tour, a buffet observations that I make of Comet Section contacts 2 lunch, prepared by CUAS was comets on the limit of the Section news 2 available, though a few people telescope and seeing conditions Section meeting (cont) 3 were dragged off to a local pub. are figments of my imagination, Near misses 6 During lunch Roger Griffin despite the fact that they seem to Tales from the Past 7 kindly showed off the 36” lie on the light curve. The Tycho Professional Tales 7 reflector. Sales stands from the catalogue now gives a good Review of observations 8 BAA, CUAS, David Early, Earth source of magnitudes down to Comet comments 12 & Sky and TA attracted much around 10.5 and these can be used BAA COMET SECTION NEWSLETTER 2 THE COMET’S TALE

Comet Section contacts

Director: Jonathan Shanklin, 11 City Road, CAMBRIDGE. CB1 1DP, England. Phone: (+44) (0)1223 571250 (H) or (+44) (0)1223 221400 (W) Fax: (+44) (0)1223 362616 (W) E-Mail: [email protected] or [email protected] WWW page : http://www.ast.cam.ac.uk/~jds/

Assistant Director (Observations): Guy Hurst, 16 Westminster Close, Kempshott Rise, BASINGSTOKE, Hampshire. (and also Editor of RG22 4PP, England. The Astronomer magazine) Phone & Fax: (+44) (0)1256 471074 E-Mail: [email protected] or [email protected]

CCD Advisor: Nick James, 11 Tavistock Road, CHELMSFORD, Essex. CM1 5JL, England. Phone: (+44) (0)1245 354366 E-mail: [email protected] or [email protected]

Photographic Advisor: Michael Hendrie, Overbury, 33 Lexden Road, West Bergholt, COLCHESTER, Essex, CO6 3BX, England Phone: (+44) (0)1206 240021

Subscription to the Section newsletter costs £5 for two years, extended to three years for members who contribute to the work of the Section in any way. Renewals should be sent to the Director and cheques made payable to the BAA. Those due to renew should receive a reminder with this mailing.

Section news from the Director

Dear Section member, devote time to papers for the to have many of the present day Journal. My paper on the comets comet discoverers at the meeting, The announcement on the IAUC of 1994 and Michael Hendrie’s so it will be a chance to meet of the likely close approach of paper on comet Bennett have been them, and to discuss ways of asteroid FX11 has promoted a lot accepted for publication. I have improving our observations. The of bitter discussion. It is a pity started on the comets of 1995 and stock of Section Observing that many of the contributors do if you have any material not Guides is probably sufficient to not realise the amount of time and previously submitted do let me last the year, but it will soon be hard work that the team at CBAT have it. Michael Hendrie is well time to think about reprinting it. devotes to verifying observations advanced on his papers on comets If you have any suggestions for and claims of discovery. In this Kohoutek, and Kobayshi-Berger- changes or additions do let me particular case it was fairly Milon. Kenelm England is know. obvious to any regular observer looking at the possibility of that the initial observations writing a paper on the Kreutz There is always a great desire to showed a close approach, but few group comets. If anyone would be the first to see a returning new observations were coming in like to contribute a paper to the comet, the last to see a departing and Brian Marsden wanted some Journal there are plenty of one, or to push the limits of the immediate action before the moderately bright comets which telescope and observers asteroid faded. Goliath in the still await a report. I’d also love capability. The ready availability shape of NASA immediately to see some contributions for the of PC planetarium programs with stepped in, and is now threatening newsletter, as it is often a solo the ability to plot comet paths to control release of all future effort, with perhaps one or two against Hubble or Hipparcos star orbital predictions. Fortunately member’s contributions. fields make it very easy to amateur astronomers and the observe exactly where a faint internet make it unlikely that they The Section meeting was a useful comet should be. Looking for would be able to keep such gathering and I was glad this time this faint smudge of light at the information to themselves. It is to have more of a chance to chat limit of the telescope’s light grasp also worth remembering that with you. The next big meeting is it is possible to convince oneself Goliath came to an unexpected the International Workshop on that something is there and to end! Cometary Astronomy, which will produce an observation of it. It take place over the weekend may well be there but such Its been a very quiet six months following the total eclipse next observations should always make for comet discoveries, with only year. I’m arranging it quite clear that there is some SOHO producing them in accommodation at a Cambridge uncertainty by putting a colon (:) abundance. The Section Meeting College and there will be full after the magnitude and noting the kept me busy for a while, but the details about booking in the next observation as reliability 3. winter has given me a chance to issue of the Newsletter. We hope Comets do outburst and others BAA COMET SECTION NEWSLETTER 1997 MAY 3 fade more slowly than expected, are properly dark-adapted, or it Haakon Dahle, Stephen Getliffe, but quite a number of may be possible to pick out Guus Gilein, Bjoern Granslo, observations are appearing on the features in the inner coma more Valentin Grigore, Roberto Haver, Internet, which appear to easily. All comet magnitude Andreas Kammerer, Heinz contradict CCD observations and estimates should be made with the Kerner, Atilla Kosa-Kiss, Martin visual observations made with eyes fully dark-adapted to the Lehky, Romualdo Lourencon, larger apertures. These prevailing conditions. Jean-Claude Merlin, Vasile Micu, contradictory observations are Herman Mikuz, Andrew Pearce, often made with moderate Since the last newsletter Josep Trigo, Vince Tuboly, and apertures and the magnitudes observations or contributions Seichi Yoshida. quoted are usually at the limit of have been received from the the telescope light grasp. They following BAA members: Comets under observation were: may be true, however the human 29P/Schwassmann-Wachmann 1, imagination is a powerful thing. Sally Beaumont, Paul Brierley, 43P/Wolf-Harrington, Denis Buczynski, Michael 55P/Tempel-Tuttle, Something that I have noted after Foulkes, Maurice Gavin, David 62P/Tsuchinshan 1, 65P/Gunn, using a computer at the end of an Graham, Werner Hasubick, 69P/Taylor, 78P/Gehrels 2, observing session and then going Michael Hendrie, Guy Hurst, 103P/Hartley 2, 104P/Kowal 2, outside again, is that I can initially Nick James, Albert Jones, John 128P/Shoemaker-Holt 1, see the orange sodium sky glow Mackey, Nick Martin, Martin 129P/Shoemaker-Levy 3, quite clearly. As my eyes dark- Mobberley, Bob Neville, Detlev 132P/Helin-Roman-Alu 2, adapt this appears to go away, but Niechoy, Gabriel Oksa, Roy C/Hale-Bopp (1995 O1), is presumably still there. I Panther, Jonathan Shanklin, C/Mueller (1997 D1), C/Meunier- imagine that this change is due to James Smith, David Strange, S M Dupouy (1997 J2), C/Utsunomiya the shift between photopic Trafford, Dan Vidican, Alex (1997 T1) and C/Stonehouse (daylight, 555-nm) and scotopic Vincent, and Peter Wroath. (1998 H1). (dark, 510-nm) vision and it clearly has an implication for and also from: Jose Aguiar, Jonathan Shanklin observing. Some comets may Alexandr Baransky, John Bortle, actually be easier to see before we Reinder Bouma, Matyas Csukas,

Section Meeting

Continued from page 1 a complete description. The ICQ reflect 100 times less light from procedure is also to report the the Sun and are similar in Guy Hurst spoke next about longest tail as the main one, reflectivity to large lumps of coal. reporting the observations. He which can give inconsistent Most of the known ones are had received about 3500 reporting when a variable length around 23rd mag in the R-band observations of Hale-Bopp and gas tail is seen with a dust tail. although the largest recently although 90% of these came by e- The apparent position angle of the discovered reach 600 km diameter mail a lot them did not use the TA tail also influences the perceived and as bright (sic!) as 20th mag. or ICQ standard, or used appearance and evening and They have a mix of names, malformed variants. [I have morning impressions of Hale- including centaurs, plutinos and placed a data entry program, Bopp were often quite different. cubewanos. Centaurs are KBOs which produces the correct format Relatively few reports mentioned between Uranus and Saturn, output, on the Section web page, the inner coma detail, yet this was typically 50 - 100 km in diameter. and it should be possible for a prominent feature of the comet. The present distribution of finds observers to download this. The Millenium star atlas, based on is biased by the presence of the Please send the TA output to Guy the Tycho catalogue, is a good Milky Way, which makes it much and the ICQ output to me. I can detailed map of the sky and the harder to find them. The original supply the program on a floppy Tycho catalogue VT magnitudes KBO discoveries needed 2.2 – for anyone who hasn’t got web are the recommended ones (coded 2.5-m telescopes (Hawaii, INT, access]. Although the report as TT), though red stars should be La Palma). Tombaugh who forms help make analysis easier, avoided. The magnitude of the searched to 18th mag, discovered they don’t record all the central condensation may be Pluto. Kowal extended the search information that the observer sees useful, though it should be made to 20th mag and discovered and a written description and clear on the report form that this Chiron. Luu and Jewitt used a drawing can help later analysis is not a total magnitude. large CCD which reached 25th and interpretation. Tail reporting mag and are now using four was a particular problem, some Mike Irwin from the Royal 4096x4096 arrays. The search observers reporting an apparent Greenwich Observatory takes part has been technology driven and length longer than would be seen in a search program for Kuiper we have only recently had the from an infinitely long tail. A Belt Objects and explained how necessary technology to carry out curved dust tail also presented he goes about discovering these wide field surveys. To find one problems: should the reported possibly cometary bodies. Pluto 22nd mag KBO we need to search position angle refer to the start, would not be classed as a planet if one square degree. CCDs are also middle or end of the tail? The it were discovered today – it is very good at detecting cosmic ICQ procedure is to report the just the largest of this class of rays – about two per minute per position angle that it leaves the solar system objects. Most KBOs square centimetre and these can nucleus, though this does not give are 10 times smaller and therefore mimic the objects being searched BAA COMET SECTION NEWSLETTER 4 THE COMET’S TALE for. Real objects can be found by highly professional presentation amateur co-ordinator. He uses a number of methods: visual commenced. Nick started by PISA for astrometry and blinking can reveal significant saying that you need to carry out photometry. motion in an hour (KBOs at 40 careful calibration of the frames, AU move at 3” per hour) and this with dark frames, flat fielding and Bob Neville now started us has been the traditional method, correction for vignetting. Terry thinking about CCD photometry. even for professionals. Three Platt’s SX series was in use by We have the problem of looking frames are needed to avoid Nick and Denis (and the Director at a diffuse object through a light confusion with cosmic rays. An and Assistant Director also polluted atmosphere. The automated search subtracts pairs confessed to owning them). The apparent brightness of a diffuse of images and looks for a high first step is to subtract a dark image changes with box size. spot close to a low spot indicating frame from the image to remove Using an image of 81P/Wild 2 movement between frames. thermal noise. Next, the image is taken on 1997 March 1 as an Telescope time has to be carefully divided by a flat field, taken at example, he showed that a 1x1 planned and search regions are twilight. A series of images, box gave a magnitude of 14.5 for selected to be near the zenith in a centred on the comet can be the central condensation. region with few bright stars and stacked together. Because of the Increasing this to 5x5 gave a high background galactic small field of view of a CCD you brighter value of 12.1, 11x11 absorption. Mike showed are generally only looking at the gave 11.3 and 21x21 (equivalent examples of images, including central part of the coma. Here we to 1’) 10.6, which was still 3 units smearing and cosmic ray defects. are interested in high frequency (on a 256 scale) above the sky The CBAT can predict future structure, so we can use an background of 20. He could positions for a month or two on unsharp mask. It is important not actually see 3’x5’ on the monitor the basis of a circular orbit and so to saturate the images, and taking so the total magnitude would be most aren’t lost provided that lots of images improves the signal even brighter, however visual there are follow up observations. to noise ratio which goes as √n. observers reported even larger There is a plan to change the A linear stretch of the original coma sizes. He had tried a couple naming convention for these image doesn’t show any detail, of mathematical models of the bodies so that there isn’t a wait of but using an unsharp mask with a coma brightness: 250 years before naming takes 15x15 median filter, dividing one –r place! Answering questions, he by the other and then stretching Ir = I0 e (a straight line on a log said that a sky survey plate was does show the high frequency plot) equivalent to a 4 Gb disk of CCD detail. Nick’s image processed in 2 data. This again is part of the this fashion showed that Hale- Ir = I0 (1/(1+r )) (a damping curve technology process as a night's Bopp changed fairly dramatically on a log plot) CCD observing can produce up to in terms of jet structure at the end 10 Gb of data. Detectors on a of 1997 January. It isn’t always The observations suggest that a fixed telescope (ie not tracking at possible to see all the detail in one damping curve is more likely. the sidereal rate) have problems single image, and several different Mathematically integrating this as with drift in non-equatorial fields techniques may be needed. As a circularly symmetric function and also if the telescope has well as processing CCD images it gives π ln(1+b2), which doesn’t aberrations. is possible to use similar converge, so a cut off is needed at techniques on scanned slides or some point, but could add to 3 – negatives, and to remove the 4m on the central value. The effects of vignetting (especially integral of the first function common in fast lenses). Offset converges to 2π, which guiding was a traditional corresponds to approximately +2m photographic technique, but it is on the central value of the 1x1 difficult and sometimes goes box. The model suggests that wrong. With CCDs short even if you sample down to 3% exposures can be stacked or made there could still be a 1m error in into a movie and Nick showed the total magnitude. A 1 in 256 clips of 55P/Tempel-Tuttle taken error in sky background by himself and Hale-Bopp taken introduces a significant error in by Terry Platt. He has written a the total magnitude. Results can batch program to process images be improved by: Mike and his co-workers have recently to get the movie sequence, which discovered two more KBOs to add to those makes life much easier. In 1. Cooling a low noise chip. shown on this plot by the Minor Planet response to a question Nick said 2. Exposing the image as fully Centre. They lie at about 1 o’clock, just that the SX is linear over 5 as possible. beyond the object shown well outside the magnitudes with a V band filter. 3. Using a range of exposure orbit of Neptune. times to avoid saturation. After a break for tea, the theme The professional Starlink 4. Using LPR filters (note that switched to amateur CCD organisation has written image the Johnson V magnitude observations and Nick James put processing software which band includes the sodium D the BAA laptop through its paces normally runs under the unix line). for the first time in anger. After a operating system, but a version is 5. Careful attention to flat few minor glitches with the IOA available which runs under PC fielding. projection system, views of the linux. This has been made 6. Find an area with similar laptop screen appeared on the available to the amateur background to obtain sky main projection screen and the community and Nick is the UK subtraction. BAA COMET SECTION NEWSLETTER 1997 MAY 5

7. Persuade software writers to commented that whilst became practical for astrometry produce variable size/shape researching his paper he found on amateur telescopes. They also aperture for photometry. that old Journals record much enabled shorter exposures to be 8. Try for darkest skies at more in the way of discussions at used, so the problem of offset midnight with the comet at meetings, something that is rather guiding was largely overcome and the zenith! lacking in modern times. [At this several people in the UK point I started making more note (including Mark Armstrong, Nick Bob concluded by suggesting a of discussions….]. Projection of James, Stephen Laurie, John project to try and correlate visual a photograph onto graph paper Mackey, Martin Mobberley, Bob and CCD observations, was tried as a method, but the Neville and Denis himself) are particularly with a view to computation of positions was now contributing observations. quantifying the degree of difficult and the observers of the Future improvements include new condensation in terms of time generally distrusted catalogues such as the USNO, photometric profiles. photographic methods. Gerald GSC #2, and new software such Merton (1945 – 1958) was a as astrometrica. Easy electronic Our final main speaker was Denis supporter of photographic communication now makes Buczynski who presented an methods which he said were twice astrometric observations almost illustrated history of the BAA as accurate as visual if done routine, however there is a need involvement in cometary properly. Reginald L Waterfield, to go to fainter magnitude comets. astrometry. Today, measurement who had been observing comets The BAA has a hard earned of images is almost a kids since he was 13, made a plate reputation and we should not rest computer game, with a click of measuring machine from bits on our laurels. the mouse and it is done. But it cobbled together from the waste has taken some getting there and bins of Oxford and Cambridge Nick James commented that the it was a very different storey in Universities. He was active in the USNO catalogue was possibly not the past. Then it was a laborious field from 1936 to 1986, despite as good as it looked. Dennis task of using a measuring being crippled by polio, and Buczynski wondered if there was machine, now we can use a PC reported his first position in 1939. any point in photographic and make more, quicker, fainter Very intricate steps had to be astrometry. Michael Hendrie and more accurate measurements. followed just to get the position of thought probably not as CCDs A C D Crommelin was the 3rd the reference stars (63 steps for were so much easier. Guy Hurst Director of the comet Section and just 3 stars), even before starting noted that not many, if any, reigned from 1897 to 1939 (I have the positional measurement of the positions were now reported no intention of serving this long!). comet. Michael Candy was photographically. His photograph clearly showed Director from 1958 – 1968 and that it was essential to have a long discovered a comet in 1960 whilst David Graham concluded the white beard to be a Victorian testing an eyepiece. Brian formal session with slides of his professional astronomer. Marsden, a Cambridge graduate, 6” reflector and 16” f/5 was a section member, working Newtonian that he’d used to view on comet orbits and now heads Hale-Bopp. He showed well the CBAT. Michael Hendrie executed drawings of the jets and participated in Waterfield’s shells seen with a magnification observations and eventually built of x200 and described the his own measuring machine and experience of standing in a dark telescope. Harold Ridley used a graveyard with the comet hanging Zeiss measuring machine, over the church. His final slides purchased by the BAA, which is showed the comet with bright now used by Glyn Marsh. Brian zodiacal light. Manning became interested in measuring positions as a result of It had been clear all day, so after seeing measurements published in downing a fortifying cup of tea or TA, and obtained very accurate coffee we headed for the results, receiving an IHW award. Northumberland and Denis started in 1984, encouraged Thorrowgood telescopes, hoping by Waterfield and has continued to have views of Saturn and to date. The number of 55P/Tempel-Tuttle as the twilight measurements dropped in the faded. Saturn was easily acquired 1970s, particularly after 1978 in the Northumberland, but I had He predicted the return of when they were no longer trouble with 55P in the 1P/Halley to within three days, routinely reported on IAUC, Thorrowgood. Using the which earned him an honorary however PCs have revolutionised traditional technique of star degree from Oxford (despite the position. It is important to be hopping I found the field being a Cambridge graduate). His timely, and the IHW asked for 48 relatively easily, but was a bit main interest was positional hours turnaround, which was perplexed that the fainter stars measurement and there are few often bettered despite virtually all seemed to be disappearing. A descriptive accounts of comets observations being photographic. quick check of the OG showed it from this period. Observers used Better catalogues have led to wasn’t dewing up, but a look filar micrometer measurements, better positions. Before the PPM outside showed that cloud was which have a personal error, need there were not many stars, hence a coming in. The East was still a time source and the positions of wide field was needed. The GSC clear, but we couldn’t move the the reference stars. Denis has many stars and so CCDs slit, so I took the group down to BAA COMET SECTION NEWSLETTER 6 THE COMET’S TALE my 0.33-m Odyssey Dobsonian. I The Northumberland refractor Melvyn Taylor at the meeting. couldn’t manage to find M35 in photographed on a time exposure by Neil Fortunately Melvyn attended the Gemini, but did succeed in Boyce and Tony Darlison out of London meeting in locating M42! Birmingham at the end of April Thanks to all those making the and I was able to present it to him journey to Cambridge, and then. Melvyn has been particularly to the speakers, contributing observations to the CUAS and the IOA for making it Section for over 25 years and also such a worthwhile meeting. makes extensive contributions to There will be a meteor Section the Meteor and Variable Star meeting here at the end of Sections. Very often such October and there is to be an ICQ stalwarts of the Association International Workshop on receive little thanks for all their Cometary Astronomy in August hard work and the Keedy award 1999 following the total eclipse. makes a fitting tribute.

Inevitably I was going to forget Jonathan Shanklin something, and I should have presented the Keedy award to Close-Approach Comets

The table lists close approaches to the Earth by comets observed prior to 1998 March 31 and those predicted to occur up to 2031. The table is sorted by close-approach distance from closest to farthest. Only past close-approach distances less than 0.11 AU are included in the table. The table is taken from the web page by Alan B. Chamberlin of the Solar System Dynamics Group at the Jet Propulsion Laboratory, with future predictions taken from the CBAT web page.

Date of Close Distance Name Designation Earth Approach (AU) (LD) Comet of 1491 C/1491 B1 1491-Feb-20.0 0.0094 3.7 * Lexell D/1770 L1 1770-Jul-01.7 0.0151 5.9 Tempel-Tuttle 55P/1366 U1 1366-Oct-26.4 0.0229 8.9 IRAS-Araki-Alcock C/1983 H1 1983-May-11.5 0.0313 12.2 Halley 1P/ 837 F1 837-Apr-10.5 0.0334 13.0 Biela 3D/1805 V1 1805-Dec-09.9 0.0366 14.2 Comet of 1743 C/1743 C1 1743-Feb-08.9 0.0390 15.2 Pons-Winnecke 7P/ 1927-Jun-26.8 0.0394 15.3 Comet of 1014 C/1014 C1 1014-Feb-24.9 0.0407 15.8 * Comet of 1702 C/1702 H1 1702-Apr-20.2 0.0437 17.0 Comet of 1132 C/1132 T1 1132-Oct-07.2 0.0447 17.4 * Comet of 1351 C/1351 W1 1351-Nov-29.4 0.0479 18.6 * Comet of 1345 C/1345 O1 1345-Jul-31.9 0.0485 18.9 * Comet of 1499 C/1499 Q1 1499-Aug-17.1 0.0588 22.9 * Honda-Mrkos-Pajdusakova 45P/ 2011-Aug-15.40 0.0601 23.4 Schwassmann-Wachmann 3 73P/1930 J1 1930-May-31.7 0.0617 24.0 Sugano-Saigusa-Fujikawa C/1983 J1 1983-Jun-12.8 0.0628 24.4 Comet of 1080 C/1080 P1 1080-Aug-05.7 0.0641 24.9 * Great comet C/1760 A1 1760-Jan-08.2 0.0681 26.5 Comet of 1472 C/1471 Y1 1472-Jan-22.9 0.0690 26.9 * Comet of 400 C/ 400 F1 400-Mar-31.1 0.0767 29.8 * Schwassmann-Wachmann 3 73P/ 2006-May-12.00 0.0816 31.8 Honda-Mrkos-Pajdusakova 45P/ 2017-Feb-11.38 0.0829 32.3 Comet of 1556 C/1556 D1 1556-Mar-13.0 0.0835 32.5 * Schweizer C/1853 G1 1853-Apr-29.1 0.0839 32.7 Bouvard-Herschel C/1797 P1 1797-Aug-16.5 0.0879 34.2 Halley 1P/ 374 E1 374-Apr-01.9 0.0884 34.4 Halley 1P/ 607 H1 607-Apr-19.2 0.0898 34.9 Comet of 568 C/ 568 O1 568-Sep-25.7 0.0918 35.7 * Messier C/1763 S1 1763-Sep-23.7 0.0934 36.3 Tempel C/1864 N1 1864-Aug-08.4 0.0964 37.5 Wirtanen 46P/ 2018-Dec-21.03 0.0977 38.1 Schmidt C/1862 N1 1862-Jul-04.6 0.0982 38.2 Comet of 390 C/ 390 Q1 390-Aug-18.9 0.1002 39.0 * Hyakutake C/1996 B2 1996-Mar-25.3 0.1018 39.6 Seki C/1961 T1 1961-Nov-15.2 0.1019 39.7 Hartley 2 103P/ 2010-Oct-20.89 0.1198 46.7 Tuttle-Giacobini-Kresak 41P/ 2017-Mar 27.37 0.1362 53.1 BAA COMET SECTION NEWSLETTER 1997 MAY 7

* - Distance is uncertain because the comet's orbit is relatively poorly determined. LD Miss in earth-moon distance units

BAA COMET SECTION NEWSLETTER 8 THE COMET’S TALE

Tales from the Past

This section gives a few excerpts not discovering any comets when meeting and “The Computing from past RAS Monthly Notices, Mr Perrine in America had Section (which but rarely BAA Journals and Sky and discovered five in two years. contributes to an exhibition) was Telescope. represented by an unusual item in 50 Years Ago: Comet notes in the form of a notebook of some 150 Years Ago: Several issues of the January Journal commented 200 pages showing the MN carried search ephemerides, on the exceptional number of calculations of the perturbations based on computations by Mr comets that had been under of Comet Gale, exhibited by the Hind, for the expected return of observation, though only two Rev Dr C Dinwoodie.”. the comet seen in 1264 and 1556. were bright enough for those with [No such comet was seen and the moderate equipment. Comet Although not strictly relevant to 12th Catalogue lists two separate Reinmuth 1947j (44P/Reinmuth, comets my eye was caught by two comets with parabolic elements]. 1947 R1) was found to be a other items. In 1948 May “The In January Professor Challis periodic comet and there were future of the present Royal published a paper giving a method attempts by E Rabe in Germany to Observatory buildings at for computing a comet’s orbit link it to 1858 J1 (Tuttle) and Greenwich is still under from three positions. Caroline 1907 L1 (Giacobini) however consideration.” and in 1948 June Herschel died at Hanover on Gerald Merton was not “Another factor which was taken January 9th aged 98. She convinced. [Crommelin had into consideration was that owing discovered eight comets, of which demonstrated that these two to the brightness of modern street- five carry her name (1786 P1 comets were linked in 1928, but it lighting, the long exposures (Herschel), 1788 W1 (Messier), was not recovered. Lubor Kresak necessary for photographing the 1790 A1 (Herschel), 1790 H1 discovered a comet in 1951, solar phenomena could not be (Herschel), 1791 X1 (Herschel), which was identified with the lost given, and solar photography 1793 S2 (Messier), 1795 V1 comet and it is now known as plays a large part in the life of the (2P/Encke), 1797 P1 (Bouvard- 41P/Tuttle-Giacobini-Kresak.] A Observatory.”. Herschel). note in the February Journal recounted the tale of the German The November issue of Sky & 100 Years Ago: An address by astronomer von Zach who had Telescope noted that publication Andrew C D Crommelin (the new humorously advised Pons that of the Minor Planet Circulars had Director of the Section) was comets were more numerous begun at the Cincinnati published in the November when there were many sunspots. Observatory under the Journal. He divided cometary Shortly afterwards a large group Directorship of Dr Paul Herget. work into: 1) Sweeping, of spots had appeared and Pons The February issue had several estimating that 120 hours were went out and found a fine comet. pages devoted to ‘The Great required per comet, 2) The note pointed out that when Comet of 1947’ (1947 X1). It Astrometry, 3) Visual physical one of the largest sunspots ever was widely seen in the Southern observations, 4) Photography and recorded was seen at the end of Hemisphere on the evening of 5) Computation of orbits and January 1946, 29P/Schwassmann- December 8 as it emerged from Wachmann 1 had brightened to perihelion. With a tail more than ephemerides. Interestingly even th this long ago defocussing stars to 9 magnitude, so there might be 25° long, and a magnitude near 0, make them comparable to the some truth in the tale. it was a splendid sight. A few comet was recommended for days later the nuclear making magnitude estimates, and The meeting at the end of condensation was observed to be the procedure was regarded as December (recorded in the April double. The editorial also noted very difficult. Tail features were Journal) reported on 1947 X1 that Michiel John Bester, an regarded as important, with which had reached –3 on assistant at Boyden Station had photography recognised as a December 9. There had been a discovered three and shared a valuable tool for precise number of UK reports of the fourth of the year’s 14 comets. A measurements. The December comet, but in fact the object seen follow up article in the next issue Journal included a list, prepared was Venus. The Journal also looked in more detail at comets by W F Denning, of comets notes that for the first time i as and their link to meteors. There expected to return over the next well as j had been used for comet was also more coverage of the couple of years, which was designations. [In fact both were Great Comet. One observer noted originally published in Nature. At used in 1898, but generally j was that the comet appeared distinctly the March meeting Crommelin omitted to avoid confusion, as pinkish to the naked eye. castigated British observers for was i on occasion.] The April meeting was the Exhibition Professional Tales

Many of the scientific magazines the next issue so that everyone of comet Hyakutake (1996 B2). have articles about comets in can look them up. They used the Goldstone Deep them and this regular feature is Space Communications Complex intended to help you find the ones Science 1997 December 12. J K in California to detect echoes you've missed. If you find others Brown et al report on the radar from the nucleus and large grains let me know and I'll put them in detection of the nucleus and coma in the comet’s coma. These BAA COMET SECTION NEWSLETTER 1997 MAY 9 measurements suggest that the was the highest ever found in an probably around 50 km diameter, nucleus was quite small, only two IDP. This prompted Scott though the range of estimates to three kilometres in diameter, Messenger and Robert Walker to varies between 40 and 80 km, with a surface similar in try and identify the source. The with some suggestions that it may consistency to loosely packed IDPs were minimally altered by have an elongated shape or even snow. The small size agrees with heat, suggesting a low entry speed have multiple components. It other measurements and explains into the atmosphere. The low rotates with a period close to the need for non-gravitational amount of helium suggested a 11.34 hours, however the forces to fully represent the relatively recent release of the direction of the rotation axis has orbital motion, something quite material (within the last ten years, not yet been determined. Many rare in long period comets. The compared to the average lifetime molecules have been seen for the rotation period could not be of dust at 1 AU of 10,000 years), first time in the comet’s spectrum, measured, but other otherwise it would have picked up however it was a very dusty measurements suggest either 6.25 more from the solar wind. As comet making the gaseous or 12.5 hours. The centimetre radiation pressure always enlarges components harder to see. Peak sized grains in the coma seem to the orbit of dust particles, the dust production reached 400 be quite porous and were ejected source must come from closer to tonnes per second, however the at speeds of tens of metres per the sun than is the earth. Using entire mass loss during the second, probably at an angle of these constraints, and the date of apparition is probably still less some 40° to the sun. They are collection, they narrowed the field than 0.1% of the total mass. perhaps similar to very small from 17 active earth crossing Generally the comet was quite lightly compacted snowballs, comets to four which have low similar to 1P/Halley and probably though there is also some eccentricity orbits. Of the four, formed in the region between evidence for much fluffier grains only 73P/Schwassmann- Uranus and Neptune; it showed as well. Only five other comets Wachmann 3 approaches the earth many similarities with have been detected by radar: at the right time (the others are interplanetary and circumstellar 1P/Halley (15 x 8 km), 2P/Encke, 26P/Grigg-Skjellerup, dust. SOHO observed an 26P/Grigg-Skjellerup, Sugano- P/Machholz 2 and 107P/Wilson- enormous Lyman-alpha halo of Saigusa-Fujikawa (< 1 km) and Harrington). Its dust trail hydrogen, about 150 million IRAS-Araki-Alcock (16 x 7 km). intersects the earth in late May kilometres in diameter. The (producing the Tau Herculid discovery of a neutral sodium tail Science 1998 April 3 and Nature meteor shower), which would is well known, but the origin of 1998 April 23. A resume of allow just enough time for the the sodium has still to be found. highlights of the annual Lunar IDPs to sink down to the The comet will be studied for a and Planetary Science Conference stratosphere by June and July. long time to come and more held in Houston in March reports This doesn’t explain the strange results are likely to be published on the possible recovery of dust isotope ratio and final explanation in scientific journals over the next from 73P/Schwassmann- may have to wait until the decade. Wachmann 3. A converted U2 CONTOUR spacecraft visits the spy plane has been collecting dust comet in 2006. The comet makes NASA is giving people another particles from high in the a very close approach (0.082 AU) chance to send their name to a stratosphere for many years and in May 2006 when it may attain comet and back. They are making some of them have filtered into 0th magnitude, although the coma a second microchip that will be the atmosphere from outer space. diameter will be very large. carried on the STARDUST Many of these interplanetary dust spacecraft that will be launched to particles (IDPs), have a fragile, A report posted on the ESO web comet 81P/Wild 2 in February highly porous structure and are pages gives some highlights of the 1999 and will return samples of thought to come from comets. recent conference on Hale-Bopp the coma to earth for analysis. If Alfred Nier and Dennis Schlutter held in the Canary Islands. The you want to sign up, submit your of the University of Minnesota original period of the comet was name from analysed some collected in June 4211 years and the future period http://stardust.jpl.nasa.gov/microc and July 1991 and found that they is 2392 years. It may have passed hip/signup.html were relatively low in helium, and very close to Jupiter on June 7, more interestingly that the ratio of 2216 BC and the orbit is clearly Jonathan Shanklin the helium-3 to helium-4 isotopes evolving rapidly. The nucleus is Review of comet observations for 1997 November - 1998 April

The information in this report is a during the year will be published according to IAUC 6844 and the synopsis of material gleaned from in the Journal in due course. comet brightened to around 12.5 IAU circulars 6771 - 6894 and before fading in April. This The Astronomer (1997 November 29P/Schwassmann-Wachmann comet seems to spend a lot of - 1998 April). Note that the 1 was glimpsed by Andrew time in outburst and is worth figures quoted here are rounded Pearce at 14th mag in his 0.41-m monitoring with CCD cameras on off from their original published reflector at the end of December a regular basis. Observers are accuracy. Lightcurves for the 1997. Further reports suggested encouraged to check the comet at brighter comets are from that the comet brightened to every opportunity over the observations submitted to The around 12th mag in January and apparition, although it is at rather Astronomer and the Director. A then faded to 14th mag. The low altitude for UK observers. full report of the comets seen second outburst of the year commenced in mid March BAA COMET SECTION NEWSLETTER 10 THE COMET’S TALE

43P/Wolf-Harrington made an Clement Taylor from South January, a week or so after early morning apparition and Africa in December 1915. It was perihelion. It then faded, a little consequently few observations quite bright, 9th magnitude at best, more slowly than expected from were made. A small faint object, and shortly after perihelion split the mean light curve using a log r it peaked at around 13m in early into two fragments, each with a fit. The light curve was more or November and slowly faded, short tail. The secondary nucleus less the same as at the last return, though its southern declination became brighter than the primary, and its behaviour is fairly made it a difficult target for UK but then rapidly faded and the consistent. The comet seems to observers. Andrew Pearce made primary also faded more rapidly brighten more or less linearly with the final observation at the end of than expected. The comet was time, peaking a little after January. The 33 observations then lost until 1977, when new perihelion, then fading at the received so far give a preliminary orbital computations led to the same rate. Observations received aperture corrected light curve of : recovery of the B component by so far (257) give a preliminary m = 9.9 + 5 log d + 6.1 log r Charles Kowal with the Palomar standard light curve of 8.4 + 5 log Schmidt. The A component was d + 20.8 log r or a linear light not found. curve of 8.3 + 5 log d + 0.044 abs Comet 43P/Wolf-Harrington (T-15) where T is the number of 12 78P/Gehrels 2 peaked at around days after perihelion. 12th mag in December and the light curve suggests that it should have faded quite rapidly in the 13 New Year. I made a final observation of it in early February, making it 13.9 in the

Observed magnitude Observed 14 Northumberland refractor and was unable to see it mid month under very good conditions. Reports on the Internet however, suggest that 15 th Aug Sep Oct Nov Dec Jan Feb it remained brighter than 13 1997 - 1998 magnitude into March. The 60 observations give a preliminary light curve of 10.1 + 5 log d + 5.0 62P/Tsuchinshan 1 was reported log r, though the fit is not very at around 13th mag in March on good. the IAUC and on the CBAT web pages. Martin Lehky observed it at the end of the month. Comet 78P/Gehrels 2

10 65P/Gunn was observed by

Martin Lehky at the end of 1997, 11 though at 15th magnitude it was beyond the range of most 12 observers.

13 Comet 103P/Hartley 2 drawn by

69P/Taylor was found to be magnitude Observed unexpectedly bright at 12th Nick Martin. magnitude in January. It seems to 14 be slowly fading, though the 15 Comet 103P/Hartley 2 actual light curve is rather Aug Sep Oct Nov Dec Jan Feb indeterminate. 1997 - 1998 7 8 9 Comet 69P/Taylor 88P/Howell was brightening quite 10

10 rapidly in the early spring 11

according to estimates posted on 12

11 the CBAT/ICQ web page. This 13 Observed magnitude Observed suggested that the comet might be 14

12 observable by the end of April 15 and I made a tentative observation on April 28.9 with the 16 13 17

Observed magnitude Observed Northumberland refractor, making Aug Sep Oct Nov Dec Jan Feb Mar Apr May it around 13.2:. Other 1997 - 1998 14 observations will be needed to confirm this, but it should 15 Feb Mar Apr May certainly be reasonably easily 1998 visible by the end of May.

103P/Hartley 2 brightened very A series of Jupiter encounters last rapidly from around 16th century reduced q from 3.1 to 1.6 magnitude in August to a peak of AU and led to its discovery by near 8th magnitude in early

BAA COMET SECTION NEWSLETTER 1997 MAY 11

corrected for the distance from the Comet 103P/Hartley 2 Comet Hale-Bopp (1995 O1) earth]. 7 -4 -3 8 -2 Comet 55P/Tempel-Tuttle 9 -1 0 10 6 1 2 11 7 3 12 4 8 13 5 9

Reduced magnitude Reduced 6 14 magnitude Observed 7 10 8 15 9 11 16 10 11 17 magnitude Observed 12 12 -150 -100 -50 0 50 100 150 AugOctDecFebAprJunAugOctDecFebAprJunAugOctDecFebApr 13 Time from perihelion (days) 1995 - 1998 14

15 104P/Kowal 2 slowly brightened Jan Feb Mar Hale-Bopp (1995 O1) is now a 1997 - 1998 from around 14.5 in late October faint binocular object, but still to a peak of near 13 when at reasonably easy for Southern perihelion at the beginning of Hemisphere observers and will 55P/Tempel-Tuttle (1997 E1) March. It was then low in the continue to fade slowly. The was recovered visually in late twilight and this, combined with observed arc covers 1008 days December at around 13th mag. bad weather prevented many with observations made on 682 We will not see it again for further observations. 33 days. The equation -0.73 + 5 log another 33 years. It brightened observations give a preliminary d + 7.79 log r fits daily means rapidly and peaked at 8th light curve of 10.5 + 5 log d + very well, but there are long magnitude in late January around 11.8 log r. period variations about this mean the time of closest approach to the light curve of around a earth. It faded slowly as the

Comet 104P/Kowal 2 magnitude. Between October 20 distance from earth increased, and the end of December the although it was still approaching 10 comet faded by about 1 mag the sun. It dropped lower and

11 relative to the mean curve. lower into the twilight and was last seen around mid March at

12 about 9.5. The 186 observations Comet Mueller (1997 D1) received so far give a light curve 13 5 of 8.6 + 5 log d + 25.9 log r, 6 which is similar to that of

Observed magnitude Observed 14 7 103P/Hartley 2. A linear curve

8 shows a rather rapid brightening 15 9 with an equation of 7.9 + 5 log d

16 10 + 0.071 abs (T+4). The Hubble Oct Nov Dec Jan Feb Mar 11 Space Telescope has determined 1997 - 1998

Observed magnitude Observed that the nucleus is only about 12 three kilometres across. 13 128P/Shoemaker-Holt 1 was 14 observed by Martin Lehky at 15 around 15th magnitude in late Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan December. 1997 - 1998

129P/Shoemaker-Levy 3 was Mueller (1997 D1) was very observed by Seiichi Yoshida at difficult to see when it reappeared 14.5 at the end of January. from conjunction and the early light curve overestimated its rate 132P/Helin-Roman-Alu 2 was of brightening. The comet became observed by Martin Lehky at th difficult to see because it was around 15 magnitude during the very diffuse and the comet autumn. seemed to be becoming less active. The observations give a light curve of 9.5 + 5 log d + [5] log r though this is a very poor fit (curve near mag 13) and a better fit is given by either: a) 8.0 + 5 log d + [7.5] log r or b) 6.5 + 5 log d + [10] log r until Comet 55P/Tempel-Tuttle imaged October, followed by a fade of by David Strange. The two around 0.5 magnitude per month [shown as points near mag 8, data galaxies on the left of the upper

BAA COMET SECTION NEWSLETTER 12 THE COMET’S TALE frame are NGC 4490 (10.2) and Schmidt during a search program. X1, 1998 A1, 1998 E1, 1998 F1, NGC 4485 (12.3) D D Balam of Victoria noted that 1998 G2 and (provisionally) 1997 one of them was clearly cometary G3. Brighter objects are often with the 1.8-m reflector of the discovered in the real time data,

Comet 55P/Tempel-Tuttle (1997 E1) Dominion Astrophysical but the fainter ones have to wait Observatory. for the archival data to be 7 searched which runs three or four 8 Utsunomiya (1997 T1) was months behind. More details are followed into the twilight at the available on the Section web 9 end of December, but very few page. 10 observations were made after solar conjunction when it was in 135P/Shoemaker-Levy 8 (1998

11 the morning sky. It was brightest B1) was recovered by Carl Reduced magnitude Reduced 12 at the beginning of November Hergenrother with the SAO 1.2-m when it was around 9th magnitude. reflector at Mt Hopkins on 13 The 122 observations suggest a January 22 when it was 22nd 14 light curve of 6.1 + 5 log d + 19.3 magnitude [IAUC 6821, 1998 -80 -60 -40 -20 0 20 log r February 9]. The comet is Time from perihelion (days) unlikely to become bright enough

for visual observation. Meunier-Dupouy (1997 J2) Comet Utsunomiya (1997 T1) moved from the evening sky to 8 P/LINEAR (1998 G1) was the morning sky at the end of discovered during CCD survey January and since then has 9 work by the Lincoln Laboratory received very little attention. Near Earth Asteroid Research Project using the Lincoln There is a lot of scatter in the 10 observations, which makes the Laboratory Experimental Test System 1.0-m f2.15 reflector on magnitude equation a little 11 uncertain. The 190 observations magnitude Observed April 2.13 [IAUC 6863, 1998 April 6]. The asteroidal object received so far suggest a 12 preliminary light curve of 5.0 + 5 had a retrograde near parabolic log d + 7.4 log r. If this is orbit and follow-up images by 13 Warren Offutt of Cloudcroft, New followed the brightness won’t Oct Nov Dec Jan Feb Mar vary much from 12th magnitude 1997 - 1998 Mexico showed a tail but no over the coming year because the coma. Further astrometric changing distances from earth and observations showed that it is in sun just about balance. It is a 1997 T3 was named Lagerkvist- an elliptical Halley type orbit with slow moving, distant comet and Carsenty in early 1998. Uri a period of 45.1 years. The comet Carsenty and Andreas Nathues, of is around 18th mag, but won't will remain on view until the end th of the year. the DLR Institute of Planetary become much brighter than 17 Exploration, Berlin discovered a magnitude, when it reaches 19th mag cometary object on perihelion in November. Comet Meunier-Dupouy (1997 J2) October 5.1 during the course of

10 the Uppsala-DLR Trojan Survey, The most recent batch of MPC in collaboration with C-I lists 35417 observations by the Lagerkvist, S Mottola and G LINEAR team, with observations 11 Hahn. [IAUC 6754, 1997 October of 3424 asteroids of which 1463 7]. The comet was not named are new discoveries! By contrast until January 1998, when it was the same issue lists ‘only’ 2477 12 given the names of the discoverer observations by the NEAT team,

and the person who found that it 1924 by Spacewatch and 1725 by Observed magnitude Observed

13 was a cometary object [IAUC LONEOS. British observers have 6811, 1998 January 23] 39 between them and no cometary astrometry is reported from the 14 Jim Scotti recovered UK. May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May 1997 - 1998 134P/Kowal-Vavrova (1997 X2) with the Spacewatch telescope at SOHO (SOHO-47 and Kitt Peak on December 5.5 when provisionally 1998 G4) is the Some confusion occurred with the it was 22nd mag. The predicted third non-Kreutz group comet naming of comet 1997 L1 and it ephemeris required a correction of discovered by the satellite. It was is now Zhu-Balam. The comet +5.3 days. [IAUC 6784, 1997 found over the Easter weekend by was originally named Xinglong December 10] Kevin Schenk, but faded very and thought to be a main belt rapidly. So far it has not been asteroid, but was renamed in 1998 A further twelve sungrazing announced on IAUC. [IAUC 6811, 1998 January 23] comet fragments have been after the discoverer and the discovered by the LASCO Stonehouse (1998 H1) was person who pointed out that the coronographs on the SOHO discovered by Patrick Stonehouse object was cometary. J Zhu spacecraft, bringing its total to 45 of Wolverine, MI, USA on April reported observations of 5 objects comets. The new comets are: 22.3. He was observing in detected on June 4 by the Beijing 1997 H3, 1997 P3, 1997 S2, 1997 Serpens Caput using a 0.44-m Astronomical Observatory 0.6-m U1, 1997 W1, 1997 W2, 1997 reflector when he noticed a BAA COMET SECTION NEWSLETTER 1997 MAY 13 diffuse object which showed motion. There was some confusion over the reported motion, but it was eventually confirmed by Alan Hale on April 26.3 [IAUC 6883, 1998 April 26]. The discovery magnitude was put at 12 - 13, though Hale estimated it at 10.7. I observed it with the Northumberland refractor on April 28.08 and made it 11.7, coma diameter 1.1', DC s3. It will fade quite rapidly, though a provisional ephemeris is given in the observing supplement.

As this issue went to press, the discovery of SOHO (1998 J1) was announced. This is the first comet discovered by the satellite likely to be visible from the ground. By the time this reaches you it will only be visible from the southern hemisphere, and a special supplement is included for our southern readers.

For the latest information on discoveries and the brightness of comets see the Section www page: http://www.ast.cam.ac.uk/~jds

BAA COMET SECTION NEWSLETTER 14 THE COMET’S TALE

Comet Comments

Don Machholz OCTOBER 1997: With so many comet discoveries were made with comets from the Kreutz 150mm (6-inch) binoculars. Comet Comments is a monthly Sungrazing Group being column that I've been writing discovered by the SOHO satellite, FEBRUARY 1998: Of the last since 1978. I started writing it to amateurs have taken a renewed 100 visual comet discoveries, inform other amateur astronomers interest in sweeping along the amateurs using refractor of new comet discoveries and to path by which these comets are telescopes made 23. The smallest provide information so that they arriving. That path is now in the was Genichi Araki's 3" scope to can find the brighter comets. morning sky, having been behind find Comet IRAS-Araki-Alcock. Each issue of Comet Comments is the sun this past summer. The Toshio Haneda used a 3.3" written three weeks before the comets are very faint in the weeks refractor to find his comet and "due" date, giving time for it to be before perihelion and it may take three other instruments were from distributed to the editors and CCD imaging to capture them. 4.8 to 5.2 inches in diameter. The placed into the newsletters. The brightest members, although remaining 18 refractors were 6" in Comet Comments contains rare, can still be discovered size, with William Bradfield information about new comet visually. finding 12 comets since 1975 discoveries, followed by comet (and two before) with his 6" news and observing tips for the NOVEMBER 1997: Since the telescope. comets currently visible. Carried first day of 1975, 76 comets have in only one newsletter (the San been visually discovered. Some MARCH 1998: Amateurs using Jose Astronomical Association's have been discovered by more reflectors made forty-eight of the "Ephemeris") for the first two than one person: ten by two visual last 100 visual comet discoveries. years, the column is now carried discoverers and seven by three. They range in size from 4" to in some three dozen newsletters. This amounts to 100 visual 19.5". The most popular size (16" It also appears on the Internet: discovery events. Thirty-two of aperture) was used in 16 finds. America-On-Line displays it in those 76 comets were found in the These large reflectors were also their astronomy department evening sky with 44 found in the efficient, averaging 231 hours per (Keyword: Astronomy) and you morning sky. Additionally, 42 find compared with 391 hours for can find it at: were found in the north of the all visual comet discoveries. All http://members.aol.com/cometco celestial equator with 34 found five accidental comet discoveries m/index.html. south. All of the 23 comets found (Berger, Milon, Hale, Bopp and by observers living south of the Tillbrook) were made with JULY 1997: Of the 97 visual equator were found in the reflector telescopes. comet discovery events since southern celestial sky. Northern 1/1/75, during which 73 comets Hemisphere observers found APRIL 1998: Of the 100 comets were found and named, only four comets both north and south of visually discovered since 1975, times was the comet found by the equator. only one was found without the accident. In early July 1975 use of a reflector, refractor or Doug Berger and the late Dennis DECEMBER 1997: Since January binoculars. It was Merlin Milon found a comet while 1975, 48 different individuals Kohler's comet discovery on Sept. observing M 2. A comet hunter have visually discovered comets 3, 1977. He used an 8" (Toru Kobayashi of Japan) had that now carry their names. What Dynascope Schmidt Cassegrain. found it the previous day. Then, countries do they live in? This discovery took about forty twenty years later Alan Hale and Twenty-three are in Japan, nine hours of sweeping. Mr. Kohler is Thomas Bopp chanced upon a reside in the USA, with four in now retired and still living in new comet near M 70. Australia. Other countries Quincy, California. represented are the old USSR, AUGUST 1997: With Tabur's Canada, England, South Africa, Advertisement: To purchase my find, six of the last seven visually- Philippines, Italy, New Zealand 88-page book An Observer's discovered comets have been and Norway. The most discovery Guide to Comet Hale-Bopp for found south of the celestial events occurred in Japan (33) $12 plus $3. S&H, send a check equator; and 14 of the last 17 followed by the USA (30) and to me at: P.O. Box 1716, Colfax, visually-discovered comets have Australia (19). CA. 95713. Also available: A been found in the morning sky. Decade of Comets and Messier JANUARY 1998: Of the last 100 Marathon Observer's Guide. SEPTEMBER 1997: Many people visual comet discoveries, quote the 1700 hours it took me to amateurs using binoculars made Don's Comet Hunting Hours: find my first comet or the 1742 28. The smallest pair of 1975-1997: 6277.25 hours to find my second. This has binoculars used was 7x35's by Hours through Mar. 1998: 21.50 been surpassed twice in recent William Bradfield in 1980 to find Total hours at last discovery (10- years. In 1987 Noboru Nishikawa a magnitude-six comet. Three 8-94): 5589.00 took 3024 hours in 2389 sessions were the 80mm size while six Least hours in any month since I to find his first comet (1987a). In finds were made using binoculars began comet hunting on 1/1/75: 1990 Yuji Nakamura discovered with objectives of 110-120 mm. 4.00 (02/98), 4.50 (01/86), 5.50 his first comet after searching Four finds were made with my (02/80) 2236.5 hours in 1558 sessions. homemade binoculars (130mm), and half (14) of all binocular BAA COMET SECTION NEWSLETTER 1997 MAY 15

Most hours in any month since I began comet hunting: 69.25 (05/76), 63.00 (05/78)

BAA COMET SECTION NEWSLETTER 16 THE COMET’S TALE

BAA COMET SECTION NEWSLETTER