Orwell Astronomical Society (Ipswich)
Comet C/1986 V1 (Sorrells), 12 December 1986
In early November 1986, Californian astronomer W Sorrells discovered the 14th comet of 1986. At the date of discovery it shone at about magnitude 12 and was moving slowly westwards between the two stars marking the horns of Taurus (β and ζ Taurii). Unfortunately, a combination of poor weather and moonlight meant that it wasn't until 26 November that members of OASI observed the comet through the Orwell Park refractor. It appeared as a small, oval, hazy patch of light a few degrees north of the Pleiades. (Coincidentally, at the same date one year earlier, Halley's comet had passed a few degrees south of the Pleiades.)
By the time that members of OASI observed Comet Sorrells with the Orwell Park refractor, accurate predictions of its orbital parameters were available  and I used these to calculate its hourly motion and the PA (position angle) of its motion through to mid-December. The figure below summarises my calculations. It shows that the fastest apparent motion of the comet occurred at the end of November when it was closest to Earth. After this, although the comet was still approaching the Sun, it was receding from the Earth and its motion appeared to slow. The comet reached perihelion in March 1987.
On 06 December I took the two photographs shown below. The images are 10 minute exposures taken about 70 minutes apart. They were taken with a 15 cm f/2.7 Schmidt camera using Kodak Technical Pan film which was subsequently developed in D-19 for 6 minutes. The diagonal of each full size image (not the thumbnails) is approximately 1° and brightest star is 20 Arietis at magnitude 5.5. The comet, marked by the white triangle, appears at circa magnitude 9-10. The negatives show a distinct fuzziness to the east, indicating the presence of a tail. When the photographs were taken the comet was 180 million km from the Earth and over 310 million km from the Sun. Its motion was 220 arcseconds/hour and the difference in position between the two images is approximately 250 arcseconds. On the photographic negatives motion is apparent as trailing of the comet's image - the motion during each 10 minute exposure is about 40 arcseconds.
H B Ridley, Journal of the British Astronomical Association, vol. 95, p. 8 (1984).