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Comet Hale-Bopp (April 07, 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 April 1, 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, April 07, 1997; 11:00 UT
A brief introduction to this Update
Some of the news items presented below have already been displayed during one of the preceding days as Latest News at the ESO Comet Hale-Bopp Homepage. They are here re-edited and combined with other items of the same general category with the aim of providing a better overview of the current situation.
The information in this Update is presented under the following headings (click to jump):
1. Hale-Bopp remains an impressive sight
2. Where and when to observe the comet
3. The comet's lightcurve
4. Is the ion tail `awakening'?
5. The comet's motion
6. More about the size of the nucleus
7. The olivine grains in the coma
8. Spectroscopic observations
9. More images
10. Hale-Bopp on the Web
11. Space-based observations of comets planned
12. The return of a famous comet
13. Miscellaneous information
It is apparent that in some media, the perihelion passage on April 1, 1997 was presented as the absolute culmination of the current Comet Hale-Bopp show (expression quoted from various newspaper articles). While it is true that the comet's brightness probably reached its peak at about that time, it would be entirely wrong to believe that Hale-Bopp is no longer of interest! On the contrary, it now appears that the exceptional, total brightness persists and also that the tails are developing further, see below.
It is therefore strongly recommended to have another look at this Great Comet, before the moonlight again begins to interfere, a few days from now.
John Bortle (Stormville, NY, USA) provides this recent, detailed observational account on the International Comet Quarterly Descriptive page : Apr. 5.03: to the unaided eye, as viewed in-focus, the comet's head matches the star Rigel (at a similar altitude) in brightness; ion tail 13 deg in p.a. 19 deg, dust tail 19 deg in p.a. 12 deg; w/ 7x50 B, coma dia. 15', DC = 9, very broad dust tail has several components or layers of brightness; w/ 41-cm L (70x), coma's sunward radius is 5'.5; brilliant non-stellar nucleus surrounded by three bright envelopes, inner-most joined with nucleus at p.a. 246 deg; most of coma, plus nucleus, distinctly yellow or orangish-yellow in color; great dust streamer in tail very weak tonight; weak void or darkness in center of tail; telescopically, central axis of comet measured to be at p.a. 24 deg.
For more information, take a look at the latest News Bulletin from Sky and Telescope , updated every Friday.
Here is a link to the map of Hale-Bopp's trajectory in April [JPEG; 65k] by Sky & Telescope .
Several visitors to the ESO website who are located in the southern hemisphere have been asking when the comet will become well visible from the south.
According to the Observing Guidelines by Sky & Telescope (where you will find the full details, including a section entitled `The View from the Southern Hemisphere'), by about the end of April, viewers in South America, South Africa, Australia, and New Zealand should be able to catch sight of the comet very low in the northwest in early evening hours. In any case, the comet will cross the celestial equator on June 26, but it will then be very close to the Sun in the sky (22 o ) and not easily observable. Later in the year, however, southern observers with small telescopes will be able to enjoy it when it moves outwards.
The mean of 11 estimates of the brightness on April 4-5 is -0.7 +- 0.2. This shows that the magnitude has remained virtually unchanged since perihelion, one week ago.
The most recent lightcurve, currently available on the Web, is that from IAC (Canary Islands, Spain), maintained by Mark Kidger and, whenever possible, updated every day. A preview-version (GIF; 6k) , at this moment updated with observations until April 5, is available here. It shows a large spread in the estimates around perihelion, reflecting the inherent difficulty of such estimates as well as the different methods of the observers.
Mark Kidger has also prepared a comprehensive summary of the brightness development including a comparison of Hale-Bopp with other comets.
The dust tail continues to appear comparatively diffuse, although there are interesting structures that are well visible on high-resolution images. The total length, as seen on a dark sky background, is estimated at about 15 o.
After a period of relative tranquility, there are now signs of increased `activity' in the plasma (ion) tail, most probably as a result of the comet entering more `turbulent' regions where the rapid particles in the solar wind interact with those from the comet. Look for instance at the image from Crni Vrh (half-size preview version; JPEG - 29k) , obtained on April 2 by Herman Mikuz and his colleagues there. Access their Hale-Bopp site to get the full-size version, in which many fine details are visible.
A report has been published by Louis S. Binder , Optometrist and a member of the Fort Bend Astronomy Club and Houston Astronomical Society Clear Skies (Texas, USA) about the appearance of a `second ion tail' on April 5. This may well be true, although it is unsual that a comet has more than one main ion tail. However, in an active environment, some comets frequently display several rapidly changing, less prominent and rather short, `secondary ion tails', known as streamers .
Today (April 7, at 12 UT), the distance from the Earth to the comet is 1.412 AU = 211.2 million km. The corresponding light travel time is 704 seconds or 11 minutes 44 seconds. The distance between the comet and the Earth is increasing at a rate of about 20 km/sec.
At that moment, the comet is 0.921 AU = 137.8 million km from the Sun; this distance increases by about 4 km/sec. The comet's orbital speed is about 43 km/sec.
On IAU Circular 6609 (April 2), H. Matthews (JAC, Hilo, Hawaii and National Research Council of Canada) and colleagues report about the first images of Comet Hale-Bopp obtained with the SCUBA bolometer array at the James Clerk Maxwell Telescope on Mauna Kea: Images taken at 850 microns on Mar. 30.92 UT show an approximately spherical coma that is extended relative to the 14 arcsec diffraction-limited resolution..... The surface-brightness profile appears slightly steeper than expected on the basis of steady-state ejection. The inferred central excess (210 mJy) places a strong upper limit of 49 km to the radius of the nucleus. This limit is slightly larger than that inferred from observations in 1996 with the Hubble Space Telescope and recently reported.
Jacques Crovisier informs that the recent Science paper on ISO results (Crovisier et al.) is summarized in an ESA Information Note that may be accessed at: http://isowww.estec.esa.nl/activities/info/9710.html.
It also points to a spectrum of comet Hale-Bopp from 6 to 45 microns which identifies crystalline forsterite (Mg-righ olivine) as a constituent of cometary dust. It compares the main cometary volatiles (H 2 O, CO, CO 2 ) observed in the IR spectrum of the comet with insterstellar ices and analyzes in some details the spectrum of water.
No further observations of new molecules have been published during the past days. However, a most interesting Hale-Bopp website with related information has been set up at the Institut de Radio Astronomie Millimetrique (IRAM) in Grenoble (France) whose powerful antennas in France and Spain have been repeatedly used to observe this and other comets.
The site includes a comprehensive graphical presentation (here reproduced in reduced format for preview [GIF; 5k] ) displaying the evolution of the molecular production rates of Hale-Bopp with heliocentric distance. Filled symbols with error bars correspond to detections, open triangles are upper limits. OH: black squares; CO: green circles; CHOH: blue squares; HS: red triangles; HCO: green squares ; HCN: black triangles; CS: red circles); CHCN: dark blue triangles; HNC: blue triangles. The vertical bars at r = 1 AU correspond to the ranges of molecular abundances measured in previous comets near perihelion. This clearly demonstrates the exceptional activity of Comet Hale-Bopp.
A new site that is frequently updated with new images is now avialable at IAC (Canary Islands, Spain). The Last Image site will be updated automatically as new images become available from the Mons telescope. You may also like to see an Infrared Image (more will be added to this page as they are reduced).
More fine images have become available at the Soenderborg site (here is the latest image from April 6 ). They are made by the students at a high-school, together with a veteran photographer Bernd Schatzmann and their teacher, Mogens Winther . And try these two sites for interesting and well-presented information with images: AMPO (Florida, USA) and Tuomi (Georgia, USA). More images have also just been posted at Bob Yen's site.
New images by Josef Anzer, Andreas Rodoschegg and Peter Staettmayer are available at http://telepath.gsf.de/~voss/1995O1/Fotos.html.
Some of the best observing conditions are those you find on the glaciers in the high Alps in Europe. A group of amateur astronomers from Tyrolia (Austria) has become quite known in the Central European area for their photographic expeditions into such territory. Many of their impressive images may be accessed at their German-language Hale-Bopp page ( here a small-size preview - 54k ). Don't worry about the spelling mistake in the cxomet's name - the images are splendid! This website also has fine views some of the very harsh places from where the photos very made (small size preview from the Nockspitze (Nock Peak) - GIF; 30k).
Several positive comments have been received from active observers about the image [GIF; 30k] by David Bridges who asked for professional advice about it (he did not want to announce a `discovery'!). It is obvious that the subsequent explanation of this `double' image as `guiding effect' has been very instructive for some of Dave's colleagues!
Following a very hectic time around perihelion, it would appear that the Hale-Bopp related traffic on the Web is now slowly abating. This is most likely a combined result of exceptional media interest at that time and a certain `saturation' - by now, many people have seen the comet and realised that it does not look very different from evening to evening. In fact, many members of the public may have gotten the impression that it is quite normal that a bright comet like Hale-Bopp should be visible for such a long period! If so, they do not fully understand how privileged we all are at this moment.
Nevertheless, the overall interest in Hale-Bopp is still very high and the number of hits per day at the ESO site runs into tens of thousands.
How many Hale-Bopp sites are there on the WWW? Nobody knows for sure, but when running the search Engine at the AltaVista site with the search string `Hale' NEAR `Bopp' (i.e., the word Hale is within 10 words of the word Bopp , ensuring that the document really refers to the comet) results in about 6000 documents matching the query! It is obvious that not all of these are bona-fide Hale-Bopp sites, but the number is still impressive and clearly shows the great interest in this event. By the way, adding the word ESO to the search gave about 300 matching documents; adding JPL gave about 700.
The JPL Hale-Bopp site now comprises nearly 2600 images, mostly obtained by well-equipped amateurs. It would be interesting to learn whether use of this enormous material for scientific purposes is planned anywhere ? Although this collection is clearly very inhomogeneous in terms of resolution and overall quality for such purposes, these images do provide a continuous record of the development of the comet, in particular the tails and the major structures in the coma. Although such a project would demand a large effort, it would indeed be a pity, if this unique opportunity would remain unused!
Cometary scientists all over the world are following the preparation of space missions to comets with great interest. More information about two of these has just become available.
The Rosetta mission by the European Space Agency (ESA) aims at the soft landing on the nucleus of Comet Wirtanen in 2013, at a time when the comet is at aphelion , the point in its orbit farthest from the Sun. This will ensure that there are relatively few dust particles around the nucleus which may hurt the spacecraft and endanger this mission during the final approach.
Comet Wirtanen moves in an elliptical orbit with a period of about 5.5 years. It passed its perihelion on March 14, 1997. It is now being observed with professional telescopes, but it is a relatively faint object, especially when compared to Hale-Bopp.
Also NASA in the USA is planning a cometary mission with the Stardust spacecraft. A 1999 launch is planned that will capture samples of comet dust from the comet Wild 2 in 2004 for return to Earth in 2006. Also this comet is observable in 1997. For more information, see this report.
The Stardust spacecraft is protected from oncoming cometary particles with a front Whipple Bumper , a shield named for renowned astronomer Fred Whipple (who first described the `dirty snowball' nucleus of a comet and who recently celebrated his 90th birthday), with a composite structure that includes metals and several curtains of the same material as bullet-proof vests. However, the bumper does not offer unlimited protection against a barrage of numerous, large particles.
While the entire world is now following Comet Hale-Bopp with great interest, it has gone almost unnoticed outside professional circles that another famous comet for which recorded observations date back to the year 1366, is now being observed with some of the largest telescopes in the world.
This comet is known as Tempel-Tuttle and it is the parent body of the Leonid meteors , which are visible in early November each year. This means that the dust grains that cause the numerous `shooting stars' when they enter the Earth's atmosphere at this time, originally come from this comet. You may learn more about all of this if you read the detailed information about a collaborative project on the Leonid meteors that took place within the Astronomy On-Line Programme.
On March 10, 1997, a message was published in IAU Circular 6579 that Comet 55P/1997 E1 (Tempel-Tuttle) had been recovered on CCD frames obtained on March 4 with the 10-metre Keck Telescope at Mauna Kea (Hawaii) by Karen Meech and her collaborators. One of these, Olivier Hainaut , reported the corresponding astrometric measurements on the Keck frames and also on a frame from the ESO 3.5-metre New Technology Telescope (NTT), taken 3 days later by a group of astronomers at La Silla.
Olivier Hainaut has also prepared a composite photo; it is available here in two versions ( [GIF; 432k] and [GIF; 120k] ) and shows the point-like image of the comet's nucleus among the trailed images of stars (because the telescopes were set to follow the comet's motion). At the time of these observations, it was about 3.6 AU (540 million km) from the Earth and 4.4 AU (660 million km) from the Sun. The magnitude was about 22.5, i.e. about 60,000 times fainter than Comet Hale-Bopp was at the time of discovery at nearly twice the distance. This again shows the exceptional activity of the latter!
Comet Tempel-Tuttle has a period of 33.2 years and the earliest recorded observations which can be associated with it, were made in October 1366 by Chinese, Japanese and Korean astronomers. Among the periodical comets, Comet Halley is the only one for which earlier observations are available. It was next seen in October 1699 by Gottfried Kirch in Germany. At the return in 1866 (when it was first seen by the two observers whose names it now carries), some astronomers noted the similarity between the orbits of the Leonid stream whose bodies give rise to the Leonid meteors and this comet. This was the first time that the close connection between comets and meteors was demonstrated.
Comet Tempel-Tuttle will come within 0.356 AU (53.3 million km) of the Earth on January 17, 1998, just before it passes it perihelion on February 28 at a distance of 0.977 AU (146.1 million km) from the Sun. It is not expected to reach naked-eye brightness at this apparition, but should become well visible in small telescopes at magnitude 8-9.
The Leonid meteor shower is expected to produce a particularly spectacular display in November 1998 according to Iwan Williams (Queen Mary and Westfield College, University of London, UK). He will present his findings at the UK's National Astronomy Meeting at Southampton University on April 11, 1997. The Leonids produce grand displays about every 33 years, just after the return of the parent comet. The last time was in 1966, but 1998 could be better than 1999. (From a UK RAS Press Release of April 7, 1997)
A general question has been posed by several visitors to the ESO Hale-Bopp site (yes, it has nothing to do with Hale-Bopp or comets in general!): When does the new millennium start? As of today, there are 1000 days until January 1, 2000, and big counters are now running in some places, for instance in Paris and New York.
The astronomical answer is that the 3rd millennium starts at midnight between December 31, 2000 and January 1, 2001! The reason is that there are exactly 1000 years in one millennium; the first comprised the years 1-1000 and the second millennium ends at the end of the year 2000. As an illustration of this, you may perhaps remember, that the first minor planet, Ceres , was discovered by G. Piazzi (Palermo, Sicily) on the first day of the 19th century (January 1, 1801) .
When the third millennium begins on January 1st, 2001, an epehemris computattion shows that Comet Hale-Bopp will be located at RA = 5h 3m 59s; Decl = -80 o 18.8 (J2000-coordinates) at a distance of 12.828 AU (1919 million km) from the Earth and 12.623 AU (1888 million km) from the Sun, i.e. it will be more distant than the planet Saturn. The predicted magnitude is about 16, but this is of course quite uncertain. It should be well observable with medium-size telescopes from the southern hemisphere at 76 o angular distance from the Sun. Back to ESO Hale-Bopp Homepage