A NATURALIST LOOKS AT COMETS

 A Naturalist looks at Comets

  (Reminiscences of a Sri Lankan Comet Chaser)

  Rex I. De Silva

My interest in observational astronomy was first aroused when I bought a small terrestrial refractor in January 1968.  With it and a copy of Norton’s Star Atlas (1966 ed.) I commenced a personal survey of the night sky. More than two years passed before I saw my first comet. Perhaps in the long run this was a good thing as when a comet finally did appear I had a reasonably good working knowledge of the night sky and observing techniques.

Comet Bennet arrived in late March 1970. My first sight of it was from Havelock Town (Colombo), where I was living at the time. The comet was on the meridian in the northern sky when I first saw it in the pre-dawn hours. It was a spectacular sight with its long and impressive tail. As the comet was very bright (and in 1970 atmospheric and light pollution was minimal) no optical aid was required to view it. However my best view of it came a few days later. I was a professional diver at the time carrying out underwater operations with the legendary diver and marine biologist Rodney Jonklaas. Our dive site was the Great Basses Reef, about eight miles (c. 12km) out at sea off the coast of Ruhunu National Park (Yala). There is a lighthouse on the reef and when the (lighthouse) staff invited us to have dinner with them, we eagerly accepted. We did not return to our shore base at Amaduwa that evening but, sending our dive boat back with instructions to rejoin us the following morning, spent the night in the lighthouse. Some hours after midnight I ascended to the top of the lighthouse and, positioning myself on the light platform, in a manner that the light beams did not interfere, looked northwards at the Comet. Bennet had looked spectacular from Colombo, but when seen from out-at-sea it was absolutely fantastic! In more than four decades of stargazing and several comets later, Comet Bennet is to me, still the best!

There was a long hiatus until my next comet came along. It was the ill-fated Comet Kohutek which was preceded by a wave of media hype – it even had a few pages to itself in the prestigious "Time" magazine which considered that it would become the “Comet of the Century”. Alas it was not to be. Kohutek which arrived in 1974 did not live up to expectations, and was only visible to the naked-eye with some difficulty. Kohutek also taught me that a small refractor was not a suitable instrument for observing comets (see below) so I viewed it with borrowed binoculars.

A year later (1975) Comet Kobayshi/Berger/Milon made its appearance. This comet had the most diffuse coma I have seen, (the degree of condensation of the coma being zero on the “Crinklaw Scale”). I had acquired a porro-prism binocular which, when mounted on a tripod, enabled me to observe the comet with some difficulty. I was unable to see any evidence of a tail, although observatory photographs published later showed that a faint one was present.

The next comet to come along was West (1976). This was a splendid early-morning comet. It was easily visible in binoculars and the broad fan-shaped tail was quite an impressive sight. As the days went by it moved into the dawn sky and, to my later regret, I stopped observing. A few days later the nucleus split into four; but I missed the event although I do not know if it would have been visible in my binoculars had I been observing. West was the last comet I was to observe from Colombo.

A long period of astronomical inactivity due to other commitments meant that I missed several comets in the early 1980s. I had moved to my new home in Dampe (near the Bolgoda Lake, Station ref: SXT 94) when Comet Halley came along in 1985. It was nine years since I had seen my last comet. Halley arrived accompanied by much fanfare and media hype. It was easily visible in binoculars and even the naked-eye. However the geometry of Sun-Earth-Comet ensured that Halley was not really outstanding. This however did not prevent people, who had apparently never looked at the night sky before, from unscientific and unbridled speculation. More than one observer mistook the globular star cluster Omega (ω) Centauri, for either Halley or a “new” comet. Others claimed that the comet moved in a constantly changing orbit! Reading up on the history of comets, made me realize that “Comet Mania” often accompanies the arrival of a bright or well-known comet.

Comet Wilson appeared in 1987. It was fairly bright and easy to see in binoculars, but I cannot recall anything very special or spectacular about it.

And then in 1990 there was Comet Levy. I saw Levy in binoculars, and some claimed to have seen it with the naked eye although I was unable to do so. I will always associate Levy with our old cat “Punky”. We were having dinner when, on an impulse, I decided to look for the comet. Leaving my meal unfinished I rushed out with binoculars and after only a minute or two of searching located the comet in the south-eastern sky. Seldom have I found a comet so easily. I called to my wife and daughter and we watched the comet for some time. On returning indoors we found Punky on the dining table finishing off our dinner. This reminds me of David Levy’s statement which goes something like this “Comets and cats are alike; they both have tails and both do exactly as they wish”. (Punky passed away many years ago. We will never forget her).

The next comet was Hyakutake which appeared in 1996. I first saw it when I was travelling at night on the way to Bundala National Park to conduct a waterbird survey. A fellow ornithologist Dushyantha and I stopped at the “Tangalle Wela” (a wetland just outside the town of Tangalle) sometime after midnight. The comet was almost overhead and we watched it in binoculars. The dark site helped to make this observation a memorable one. The comet was very bright, its head showed at least two “envelopes” and a long tail. An interesting adjunct was that our vehicle driver refused to look at the comet and warned us that bad luck would befall anyone who looked at it. However we were lucky and didn’t even have a flat tire. Comet Hyakutake was magnificent; of all the comets I have seen it was only surpassed by Comet Bennet.

Hyakutake was followed in 1997 by Comet Hale-Bopp. I first detected the comet from my home in Dampe and later viewed it from the beach at Mount Lavinia. I used binoculars and a spotting scope for most of the observations. I was joined in several of these observations by a friend from Colombo University. One night while watching Hale-Bopp, I thought that I also sighted Comet Kopff, which was reportedly in the vicinity. I showed the (putative) comet to my friend Kirthi. In retrospect I have often wondered whether I actually observed Kopff or confused a faint nebula or unresolved star cluster with the comet. As I was never able to verify this one way or the other, I do not count Kopff among my “trophies”.

By the year 2000 our skies had been “dimmed” somewhat by atmospheric and light pollution and possibly the Asian Brown Cloud. Whereas on a clear night in 1984 I could easily see the Milky Way and sixth magnitude stars with the naked eye, this was no longer possible. At present the Milky Way is seldom visible from my home and the faintest star I can see with the naked eye on most nights is around magnitude four with magnitude five on exceptional nights. (Lest it should be suggested that it is my ageing eyes that have dimmed and not the skies, I can only confirm that from a dark Dry Zone site I can still see the Milky Way and sixth magnitude stars without any great difficulty so long as I wear my spectacles).

In 2004 Comet Neat came along, but, due to poor viewing conditions, merely sighting the comet was achievement enough. Interestingly, when I first detected the comet I called my old friend Professor Sarath Kotagama (the renowned ornithologist) on his mobile phone and gave directions which enabled him to find the comet, using binoculars, which he was then able to show to his family.

Comet Machholz in January 2005 was another comet which would have looked better from a really dark-sky site. Once again observing conditions were rather poor so just seeing the comet was satisfying enough. The comet was visible high in the West at around 20h00 and I was able to follow it for several nights. Once again I was able to direct Professor Kotagama to the comet using the same procedure as described for Comet Neat (above).

Comet Holmes appeared in October 2007. Sky conditions were poor due to intermonsoonal conditions and a waning moon. I received a telephone call from the astrophysicist Dr. Kavan Ratnatunga who informed me that he had glimpsed the comet through thin clouds. My wife and I went outdoors and soon sighted the Comet, which was rather bright, in the breaks between the clouds. Some astronomers call these breaks “Sucker holes” for obvious reasons. Holmes was another fairly diffuse comet without an apparent tail. This was the result of the Sun-Earth-Comet configuration which meant that we were viewing the comet “head on”                                                   and therefore could not see any tail.

Then in February 2009 Comet Lulin made made its appearance. This was another faint comet which did not live up to my expectations mainly because of light and atmospheric pollution. My wife and I were able to observe it using my trusty old Swift Audubon binoculars although it was almost invisible in my telescope.

Finally in October 2010 Comet Hartley 2 made its appearance. My wife and I observed the comet around mid-October. Hartley was an unimpressive comet, but this may have been because I had to view it in the sky glow of Colombo which is about 12 km to the north of my observing site. We  used my old Audubon binoculars to observe it.  Comet Hartley is my 14th (possibly 15th) comet - a rather unimpressive total for nigh on 45 years of observing the Heavens.

I now await the next comet which, I hope, will be a truly bright one.Many who read this will no doubt wish to see a comet for themselves; so I will make some suggestions which I hope may be helpful. To know which comets are visible try the internet (http://www.aerith.net/comet/weekly/current.html) as well as magazines such as Sky & Telescope, Astronomy, Sky at Night etc. Good optical equipment will go a long way towards successful observation. There is some debate about the ideal instrumentation for comet watching, but it is universally agreed that adequate light-gathering-power, a wide field of view and high contrast are the sine qua non in optics for observing comets. Magnification, on the other hand is less important than it is for most other celestial objects and, in general, low powers are preferred. Without entering into (or starting) a controversy I will outline the equipment I would wish to have for my next comet. First choice would be a good porro-prism giant binocular, of say 16 x 70 or so, mounted on a sturdy tripod. (Good binoculars are often superior to telescopes for viewing comets). An alternative will be one of the short-tube refractors or large spotting scopes advertised in the astronomy and birding magazines. The 80 or 90mm (aperture) models combine adequately bright optics with portability. I would use one of these with a good low-power ocular (magnification 20 - 30x). I am not a fan of reflecting telescopes but, if I had to choose one, a 150mm f 8 model would be as good as anything. Regardless of the instrument used, since comets are often dim objects of low contrast, I would ensure that the optics are scrupulously clean and free of dust, fungus, finger prints etc., and that binoculars are properly collimated. A good planisphere and star atlas are essential accessories. Will Tirion’s Sky Atlas 2000 is the ideal, although I presently use the more compact Cambridge Star Atlas (1996 ed.) supplemented by my old Norton’s Star Atlas. I also use the extremely useful planetarium program Cartes du Ciel as it shows the positions and other details for numerous comets. Also important is a red light (ideally a LED model) which helps preserve dark adaptation when reading star charts or making notes. (Many observers now use “Swan Band filters” on their instruments. These are reported to improve visibility of most comets; however, I have no experience with these rather expensive accessories). I should emphasize that these suggestions are for those who wish to observe known comets (i.e. for “Comet Chasers”). Those who wish to discover a new comet and have it named after themselves (i.e. “Comet Hunters”) will probably require more sophisticated equipment, techniques and experience and anyway will not require my advice. Having aired my views on equipment, I must confess that over the years I have only used ordinary porroprism binoculars, a small terrestrial refractor and spotting scopes for my observations. Finally, I invite all comet observers to read Leslie Peltier’s book "Starlight Nights: the adventures of a stargazer", William Liller’s "The Cambridge Guide to Astronomical Discovery" and Joseph Ashbrooks "The Astronomical Scrapbook", all of which contain information on comets.

Unfortunately,  Sri Lanka is not really ideal for astronomical observation. One major drawback is the heavy cloud cover, especially during the monsoon season which blocks out the night sky. The progressive lessening of sky-transparency by atmospheric pollution combined with increasing light pollution may, in future, require the use of larger aperture (read: more expensive) telescopes and accessories. However the less populated areas of the dry zone and, especially the arid northwest and southeast regions as well as parts of Uva and most of the east coast will probably remain good for observation in the foreseeable future. Prior preparation and training can mitigate matters to some extent. While waiting for the next bright comet to come along, a prospective comet observer would do well to sharpen his or her skills on other comet-like objects. Observations should be preceded by dark-adapting properly (i.e. remaining in a dark place for at least 15 minutes or so to give the eyes an opportunity to increase their sensitivity to dim light). It is also useful to practise using averted vision. This means using the peripheral regions of the retina which are more sensitive to faint light than the central area which is relatively insensitive. A good start is to look for objects in the Messier (M) list. After mastering the “M” objects observers would do well to test their skills on the brighter NGC objects. Then, when the next comet comes along, they will be prepared. Of course all this will be unnecessary when a really bright comet comes along where views with the naked eye may be most satisfying.

Finally beware of "Comet masqueraders" i.e other objects which can be confused with comets. In 1969 while observing with my small refractor I thought that I had discovered a new comet. I even convinced myself that I could detect its movement against the background stars. Fortunately scientific training came to the fore and before announcing "Comet De Silva" to a waiting world, I observed the object for two more nights and realised that my "Comet" was merely the well known Wild-duck Cluster (M11) in Scutum. A salutary lesson which I have never forgotten.

 Comets Bennet and Neat images courtesy David Darling

 Other Images are courtesy of JPL/NASA/ Fred Espenak 

 Text © Copyright Rex I. De Silva. All rights reserved.

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