Accidental Comet Discoveries by Variable Observers
Comet-hunters may spend hundreds - even thousands - of hours methodically sweeping huge areas of the sky in the hope of discovering a new comet. Some, such as our own Bill Bradfield, are very successful. Others get nothing except hypothermia and insect bites. So what do you reckon the chances are that someone who observes only specific patches of sky will discover a comet?
Surprisingly, four people have picked up new comets while looking at variable stars in this century. Comet Kaho-Kozik-Lis (1936III) was independently discovered by a Mr Kaho from Japan while he was observing R LMi.
A few years later, Albert Jones (New Zealand) found Comet Jones (1946VI) while observing U Pav.
It was a long wait for the next one; until Justin Tilbrook found his first comet (C/1997 O1) while observing TV Crv. Then Peter Williams discovered C/1998 P1 in 1998 while observing EK TrA. Here's how Peter describes that evening:
Most people like to complain about the weather and, well, I guess I'm just like the rest. August is usually associated with strong winds but this year they were accompanied by driving rains which produced flooding in many areas of eastern New South Wales.
My backyard observatory at Heathcote, on the southern extremity of suburban Sydney, was partially flooded with 3cm of water when a nearby drain became blocked by garden debris. Nearly 170mm of rain was recorded at Heathcote during the first 9 days of August and I was beginning to suffer the 'DTs' from a lack of starlight.
Perhaps better known for the observation of variable stars, I have been fortunate enough to also observe a number of comets over the years beginning with Comet Bennett, the Great Comet of 1970, and sending the occasional total magnitude estimate to David Seargent of the Australian Comet Section during this time.
Monday, August 10 was the first clear night of the month so, although feeling tired after arriving home from work a little later than usual, I ventured outdoors after dinner with binoculars in hand to catch up on some of the brighter variable stars on my regular working list.
A normal night's observing at Heathcote involves preparation under subdued lighting, a naked eye nova search along the Milky Way followed by a search to near magnitude 8 in two selected areas with the 10x50mm binoculars. This is followed by the binocular variables before moving onto the telescopic stars. Each observing session can last between 30 minutes and several hours.
With the moon just two days after full there was a very narrow 'dark window' before moon rise. I had used this time for the binocular variables. After this I returned indoors to help with some domestic duties and getting the children off to bed. Domestic duties complete, I sat down with my wife, Linda, and feeling rather tired thought I may retire early for the night.
However, having been clouded out for near two weeks I felt obliged to show the 'right stuff' and check on the telescopic variables. In hindsight, this proved a wise decision.
By 9.30pm local time and with the near full moon well above the horizon, the roll-off roof of my observatory parted as I prepared for observation with the 30cm F6 Newtonian reflector.
Working through my usual sequence of variable star fields, I commenced low in the south west with SY Mus and DI Cru, followed by 8 other irregular and unusual stars in the Cru-Mus-Cen region.
Then sweeping eastward at a low 72x magnification from Alpha Cir towards the faint dwarf nova EK TrA, I almost fell of the three step ladder used to reach the eyepiece as a bright comet-like object came into view.
'Oh gosh, what have we here?' or words to that effect I muttered, knowing only too well there should be no fuzzy blobs in that area of sky.
A full millisecond or two later I forgot completely about EK TrA as complete panic set in. Was it clear in New Zealand? Was it clear in Victoria? As I shuffled through my charts to find that for EK TrA, I pondered who else may be observing this field that evening. Having located the chart I proceeded to plot the object's position then wait and look for movement.
At the time of discovery the comet appeared large, round and diffuse with no tail and a 13th magnitude stellar central brightening. Through the 20x80mm binoculars it was estimated at magnitude 9.5 but of somewhat smaller diameter than through the telescope at only 4 arcmin across.
Within half an hour clear movement towards the north west was evident so I moved indoors at near relativistic speed to seek independent confirmation. After several frustratingly unanswered phone calls, I eventually raised David Seargent of the Australian Comet Section who was able to provide verification.
At this stage even Linda, who is generally content to view the moon once every second year, left the warmth and comfort of bed to become only the third person on Earth to view the comet.
David kindly emailed the co-ordinates and magnitude estimates to the International Astronomical Union's Central Bureau for Astronomical Telegrams at the Smithsonian Astrophysical Observatory in Cambridge, USA. The CBAT replied the next day with a request for more information and additional positions to allow for establishing a preliminary ephemeris.
I had never realised how long the daylight hours are as I waited for nightfall!
Tuesday night was essentially cloudy at Heathcote except for several fortunate clear patches which allowed me to relocate the comet and establish an additional position. This was duly emailed to the CBAT.
Unknown to me, Gordon Garradd of Loomberah, near Tamworth, had learnt of the comet through David Seargent and was busy measuring the comet's position on CCD images obtained that night, providing the accurate details needed by the CBAT.
IAUC 6986 was issued on Wednesday 12th August 1998 announcing the discovery of Comet 1998 P1, much to the relief of all concerned.
Many emails and telephone calls from well wishers have since been received, topping off several days of intense excitement. My two minutes of fame have certainly been an experience I will long remember. The help, encouragement and co-operation of local identities such as David Seargent, Gordon Garradd and Rob McNaught played an important part in verifying this comet.
Looking back, however, this discovery was contributed to by a number of fortunate circumstances.
Firstly, the sky was clear and calm that evening after more than a week of strong winds and driving rain. Secondly, despite a near full moon the decision was made to observe through the telescope. Thirdly, had I delayed going outdoors a little longer I may not have observed the field of EK TrA. Finally, had I not been monitoring a non-program suspected variable a little to north of EK TrA, I may not have swept northward to low magnification and onto the comet.
Luck may have played its part. However, I like to believe - tongue in cheek - that I have been conducting a systematic search for comets, in variable star fields, while looking in the wrong direction and under full moon. Clearly, my methods have been vindicated!