Orwell Astronomical Society (Ipswich)

Comet C/1986 P1 (Wilson), 10 August - 07 September 1986

On Saturday 09 August 1986, a letter arrived announcing the discovery, by Margaret Wilson of Mount Palomar Observatory, of a new comet. (The modern designation of the object is C/1986 P1 (Wilson).) The report was somewhat confused: four observations had been made within two days but brightness estimates varied widely, suggesting that the comet had gone through some form of outburst before settling down to about magnitude 12. Predicting the path was a little difficult from so few observations but I estimated where it should be that night, set up my Schmidt camera and located the appropriate star field. Around midnight on 09-10 August I took a 10 minute exposure and developed it immediately. The following morning, having found in the photograph what I thought was Comet Wilson, I came up to Orwell Park Observatory to check the photographic charts for the area and, sure enough, there was nothing on the chart to match the object in my photograph. This was my first photo of the comet, taken only five days after its discovery.

I phoned Guy Hurst, editor of The Astronomer and national coordinator for observations of new comets, supernovae, etc. He said that up to that time only one other person, Alan Young, had succeeded in obtaining a photo (in fact, about two hours before I did). Guy asked me to send him the negative and he subsequently worked out an accurate position for the comet on August 10.001 as follows (1950 coordinates): RA 22^h 14^m.04, dec +24^d 44'.21.

Encouraged by the conversation with Guy, I decided to take more photos. Unfortunately, two weeks of bad weather meant that my next photo was not until the end of August. However, after the first observations, a more accurate path was calculated for the comet so that it was easier to predict its position prior to observing.

My images of the comet are as follows:

• 10 August 1986. A ten minute exposure taken from 23:58 UT on 09 Aug to 00:08 UT on 10 Aug. The image is a 13x enlargement from the original negative taken by the Schmidt camera; it shows the comet to be stellar in appearance and of magnitude circa 12. At this time, it was in Pegasus.
• 31 August 1986. A five minute exposure taken in hazy conditions between 21:44 and 21:49 UT.
• 06/07 September 1986. Two photographs taken 70 minutes apart showing the comet to have moved by almost 100 arcseconds across the sky. The first photograph was a 10 minute exposure taken 23:08 - 23:18 UT on 06 September and second a seven minute exposure taken 00:18 - 00:25 UT on 07 September. Again, these photographs are 13x enlargements from the original negative taken by the Schmidt camera. I was able to repeat the exercise a couple of nights later and found the comet to appear "fuzzy", in contrast with its stellar appearance in early August.

The following montage shows my photographs of the comet superimposed on a plot of its motion through the heavens between 10 August and 07 September. At the beginning of the period, the comet was in Pegasus; by late-September, it had moved into Delphinus and was predicted to enter Aquila on 06 November. During the period spanned by my photographs, the comet was still very distant: at the time of the first it was 540 million km from the Sun, and by the time of the last had moved 45 million km closer. The fact that it is relatively bright even at such distances is encouraging: predictions suggest that it should be visible in the 26 cm Orwell Park Refractor, and maybe even in large binoculars, once it crosses into Aquila and, during April-May 1987, should be easily visible to the naked eye, although only from the southern hemisphere. At closest approach to the sun, the comet will still be outside the orbit of the Earth so is unlikely to become very prominent, but nevertheless it will be interesting to follow its progress over the next year or so.

Mike Harlow

Original: Newsletter October 1986
Updated: 26 March 2023