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Comet Hale-Bopp (March 17, 1997)
MPI/ESO 2.2-m + EFOSC II (May 14, 1996)
This is a summary of recent developments around this comet; the previous was published on the ESO Web on March 7, 1997. It is based on information received directly by email and also from IAU Circulars and on other Hale-Bopp WWW pages.
Please note that during the hectic phase in March - April 1997, additional, very recent information may be displayed on the front page of the ESO Comet Hale-Bopp Homepage.
Richard M. West (ESO)
Munich, March 17, 1997; 16:00 UT
Hale-Bopp brighter than expected
Comet Hale-Bopp continues to surprise and during the last days, its brightness has risen steeper than the predictions, cf. the lightcurve by Mark Kidger (IAC, Spain) (look at the bottom of the page). In case of difficulties to get through (the cable to the Canary Islands is often overloaded), here is the latest diagram (March 17; GIF; 12k). As can be seen, the recent, unexpectedly fast increase is well documented.
Mark Kidger provides the following comments, among others: If this linear brightening were to continue to perihelion, Hale-Bopp would easily go past magnitude -2 (and then start to rival Comet West which was only poorly visible when at its very brightest), although this rate of increase surely cannot continue for much longer. Even if the light curve starts to flatten-out, as it should do, we can expect a maximum around magnitude -1.5 and certainly the comet will be no fainter than -1, although no comet should ever be relied-upon to behave itself beyond the last datum point .
At the time this Update is issued, Comet Hale-Bopp is about 198 million km from the Earth and approaching at about 6 km/sec. Just over 5 days from now, it will reach its closest point at about 197 million km and then begin to move away from us. It is now 142 million km from the Sun and the speed in its orbit is about 43 km/sec.
Comet Hale-Bopp is now becoming better visible in the evening. For detailed information about viewing conditions, check the Sky & Telescope Hale-Bopp On-line Viewing Guide ; a Sky Chart for late March with horizon is particularly useful. (This information has been added on March 18 in response to requests by several visitors to this site).
Information was received on March 11 that Synchronic Bands in the Dust Tail of Comet Hale-Bopp have now been seen, cf. the image [GIF; 120k] obtained on March 10, 1997, at the National Astronomical Observatory of Japan. They correspond to distinct outbursts during which especially much dust was released from the nucleus. It is unusual that a comet shows these structures at the present distance from the Sun (about 1 AU). Look also at the corresponding Japanese website index.
The ion tail as seen in the sky now spans an angle of the order of 15 o - 20 o , i.e. the real length is approaching 100 million kilometres! The tail appearance is characterised by the excellent separation between the blueish ion tail and the more reddish dust tail; this is due to the particular spatial geometry (current position of the Sun, the comet's orbit and the Earth). See below for reference to some splendid wide-angle photos.
Where to find more information about comets
The public interest in comets has been growing as Comet Hale-Bopp is becoming brighter and I have received quite a few emails with request for more information about this subject in general.
Several educational websites may be reached via the Other Sites' page , installed here at ESO. A very useful site for anybody who wants to learn more about other aspects of comets, is that of Karen Meech 's Education project set up at the Institute for Astronomy (Honolulu, Hawaii).
Some visitors to the ESO Hale-Bopp page have indicated that they would also like to know more about the early history of cometary astronomy. These objects were among the first to be described and the available records - mostly from China - date back to about the year -1000. You will find many interesting references to comets on the History of Astronomy pages of the Working Group for the History of Astronomy in the Astronomische Gesellschaft (the Astronomical Society of German-speaking astronomers).
In addition, I have prepared an extract from a review on Comets that two colleagues and I wrote some years ago. While this Brief History of Comets (until 1950) does not pretend to be very complete, it does give the interested reader an overview of the most important developments, up to and including the emergence of the modern ideas about comets.
Solar eclipse on March 9, 1997
It is expected that information about the observations made during this eclipse will soon be published. In the meantime you may look at some of the photos obtained via the special eclipse site in Japan.
Addition on March 18 : The first, exhaustive account of the solar eclipse on March 9 , based on observations in Siberia, has now been placed on the Web by Daniel Fischer (Bonn/Koenigswinter, Germany). You will here find many interesting `exotic' links, and also one to the SOHO images!
Lunar eclipse on March 23-24, 1997
Quite often, a lunar eclipse precedes or follows a solar eclipse by half a lunar period. This is now the case and a partial lunar eclipse will take place at the time of full moon on March 23-24, 1997.
During a partial lunar eclipse, a part of the Moon will enter into the Earth's central shadow (the `umbra') and will faintly glow in a deep red light. This time 92 percent of the Moon's diameter will be within this shadow. With the moonlight considerably reduced, observers will be able to enjoy Comet-Hale-Bopp in a darker sky. Full information about this lunar eclipse is available at Sky & Telescope , cf. in particular the map of the eclipse. The event is best visible from the American continent - in Europe it will happen in the early morning, as the Moon is about to set.
For more information about the motion of the Sun and Moon and how lunar eclipses happen, take a look at the relevant Astronomy On-Line site for the total Lunar Eclipse on September 27, 1996.
Rotation and size of the nucleus
Further observations from Pic-du-Midi by L. Jorda and collaborators confirm a main rotation period between 11.20 +/- 0.10 hr and 11.65 +/- 0.10 hr. The motion is quite complex and there appears to be a superperiod ( precession ?) of 22 +/- 2 days, i.e. not too far from the earlier period of variation of about 19 days, first observed in 1995. Images are available (IAUC 6583; March 11). A corresponding link to Pic-du-Midi has been installed from the Other Websites area.
Millimeter-wave continuum observations of comet Hale-Bopp at 150 GHz, with the Nobeyama 45-m telescope (Japan) by H. Matsuo and colleagues on March 2 and 4 have detected a compact source of emission (IAUC 6585 March 12). Moreover, on IAU Circular 6587 (March 14), J. E. Wink and colleagues report that they have detected the millimeter-wave continuum with the IRAM Plateau de Bure Interferometer (France) at 3 mm (resolution 3.5 arcsec) and at 1 mm (resolution 1.5 arcsec) on Mar. 9 and 11. On Mar. 11.4 UT... the flux can be accounted for by thermal radiation at blackbody temperature 380 K from a 1600 km 2 area, which corresponds to a sphere of diameter 45 km..... It should be noted that this is not necessarily the true size of the nucleus (it may refer to the densest part of the dust cloud), but this measurement does set an upper limit to its size.
Structures in the coma
Ring and spiral-like structures have been detected in the coma by K. Birkle and H. Boehnhardt on exposures from Calar Alto (Spain), cf. IAU Circular 6583 (March 11, 1997).
Confirming observations were obtained by the European Comet Hale-Bopp Team with the 1m Jacobus Kapteyn Telescope of the Observatorio del Roque de los Muchachos (IAU Circular 6587; March 14). The corresponding image may be accessed at IAC-site , or here ( small version [JPG; 49k] and larger version [JPG; 184k] ). The astronomers also write that the observations were taken through a CN and a blue continuum filter and.... reveal both spiral-jet and arc structures.... A bright shell is also seen in both filters 20 arcsec to the southwest of the nucleus, which corresponds to a recently separated jet.... Assuming, as in IAUC 6583, that the two arcs are ejected by the same active spot and that the nucleus rotates with an 11.47 hour period (Lecacheaux et al. IAUC 6560, Jorda et al., 6583) we obtain an expansion velocity for CN of 1.3 km/s for a 60 degree rotation between arc emissions, very close to the velocity calculated by Birkle and Boehnhardt.
Bill Matthews writes (March 12): I am an amateur astronomer, located in the central USA. I have been observing this comet for about 18 months. Observing the shells on March at 11.44 UT, in a 25-cm reflector at 110x, I was struck by the impression that I was viewing not three distinct shells, but a spiral (seen edge on). As if I was looking at part of an apple peel(peeled in spiral) held up and looked at from the side. I have not seen any discussion of such a hypothesis of the shell formation. Could it be possible, that the jet is at a latitude below the solar, or rotational axis, and ejecting material in a circle, that forms a spiral as it moves away from the coma? This would seem to explain the differing geometric centers (I think). If you have any ideas or links concerning this, I would appreciate hearing about it. Thanks for your time.
The described phenomenon is well documented in various images, e.g. from Observatoire de Haute Provence (message from Luc Arnold of March 12, who likens it with a spiral galaxy!). As far as I can tell, the explanation suggested by Bill Matthews is a most likely one, although only advanced dynamical computations can show whether this is the complete truth. I would expect that the experts in this field will soon communicate their results and I will of course report about them in due time.
On IAU Circular 6586 (March 14), A. J. Apponi and colleagues report on radio observations with the NRAO 12-m telescope at Kitt Peak on March 10: We detected the HNC J=3-2 transition at 271.981 GHz.... Observations of the HCN J=3-2 transition at 265.866 GHz suggest an abundance ratio for [HNC]/[HCN] about 0.5.
The abundance ratios of the various parent molecules detected in the coma of Hale-Bopp serve to study the composition of the nucleus. As is the case for the isotopic abundances, these studies help to discern the origin and evolution of comets ( `fingerprinting' ). It is of particular interest to compare the findings with the known abundances of atoms and molecules in interstellar clouds (the solar system - and the comets - originate from such a cloud) and the major planets.
So far, the published data indicate that the gas around the nucleus of Hale-Bopp and the Earth have similar abundances of the stable isotopes of, e.g., carbon and nitrogen, thus pointing at similar (interstellar) material in the pre-solar nebula as origin. However, in Comet Halley, a careful study (in 1986 by instruments onboard ESA's Giotto spacecraft) of the isotopic abundances of individual dust grains gave wildly varying 13 C/ 12 C isotopic ratios. This showed that the grains in that comet must have formed in very different environments, well before the solar system came into being.
Amateurs and professionals continue to take hundreds and thousands of pictures of Comet Hale-Bopp. There is now little doubt that it must by now be one of the most photographed celestial objects ever - with the possible exception of the Moon and the major planets! Many of the best images are displayed at the Jet Propulsion Laboratory (JPL) - Hale-Bopp mirror site which was established when the main site began to experience symptoms of access saturation.
Among the most impressive ones are two wide-field colour photos by Eckhard Slawik (Engineer and Art Photographer) in Waldenburg (Württemberg in Southern Germany) which have been installed at the ESO site. They were obtained with a special 6 x 6 cm camera. You may access them directly via a special page or the Local Page (which has been considerably expanded during the past days!). They are available in three versions, including high-resolution files for reproduction purposes (5 Mb; please be aware of possible problems connected to the transfer of such large files!). Enjoy the comet and the Milky Way!
Incidentally, if you want to see the best panoramic images of the entire Milky Way in different wavebands, try http://adc.gsfc.nasa.gov./mw/milkyway.html. We at ESO are glad to have contributed with the panorama in visual light!
Many visitors to this site have sent me moving impressions about their encounters with this wonderful comet and it is obvious that for many people, it has been a revelation of the beauties of the night sky. I would love to pass on all of these comments for all others to savour, but which to select in a limited space? Let me just reproduce one such message (slightly edited) which obviously touches upon some of the deep feelings experienced by many observers:
Kurt Hertha in Grünwald near Munich writes: For me The Comet was always present. I have enjoyed it above many nativity scenes and renderings of the birth of Christ. The Comet thus marks the beginning of our era. I went specifically to Bayeux in France to see The Comet on the famous tapestry. In the early 18th century The Comet received its present name name, Halley, but at the time of its last visit in 1986, this particular comet was not so impressive. During the past two decades, for me The Comet was the one I saw in March 1976 in such a majestic beauty and which has since been reproduced in so many astronomy books.
Comets are fun and thousands of eager amateur astronomers search for such objects every night, hoping that they may also one day get their name on a comet. Then suddenly it is there and shows itself to one of these patient observers who calls upon his friends and says `have a look, I think I have found something'! And in no time he becomes world-famous. Now The Comet is Hale-Bopp. It grows and grows and blossoms like a white lily. Every evening and every morning I have looked in wonder and let myself be carried away by this phantastic view. Even though it is easy to see with the naked eye, it is only in the binoculars that the incredible beauty of the gas and dust tails appear. The coma and the delicate shells elevate the view through a telescope to a very special event. Whenever I can, I take the opportunity to show it to my friends and neighbours. When they leave the telescope, I still see its image in their eyes! (The author is a famous German songwriter and an avid amateur astronomer with a well-equipped private observatory).
Here are some new links:
http://cip2.e-technik.uni-erlangen.de:8080/hyplan/cnkuhn/nhab.html (Astronomy Club in Nuremberg, Germany)
http://www.comet-track.com/hb/hb.html (Bob Yen's new Hale-Bopp page)
http://scienceweb.dao.nrc.ca/comet.html ( The Great Canadian Hairy Star Party based at the Dominion Astrophysical Observatory)
Upcoming Hale-Bopp observations
Observations of Hale-Bopp are increasing in intensity as the Comet nears its perihelion on April 1. Most of the large professional telescopes in the northern hemisphere are being used and on March 25, a sounding rocket with the Wide-Field Imaging Survey Polarimeter (WISP) of the University of Wisconsin-Madison will lift off from a pad at the White Sands Missile Range in New Mexico (USA). At the apex of its trajectory nearly 400 km above the Earth, WISP will take a series of eight pictures in ultraviolet light. Back to ESO Hale-Bopp Homepage