Published in the December 1999 issue of Universe
and the Autumn 2000 issue of Comet Tales
The Great Comet of 1811
Pons stumbled across another comet (already just visible to the naked-eye) on 11th April, 1811. This time, however, he was not the first discoverer, as Honore Flaugergues had first sighted the comet on 25th March, just three weeks earlier. Comet C/1811 F1 was found in a portion of the now-defunct constellation Argo Navis - its position places it in today's constellation of Puppis. In those days, communication was far from rapid, and Pons had not heard of the earlier discovery.
[Ask yourself this question: how long would it be before you heard about the discovery of an already naked-eye comet in the sky? Would you rely on the daily newspapers and TV to let you know, and give details of where to look? If you're not receiving the ASNSW's Astrocards, you may miss out on catching bright discoveries in time.]
At the time of its discovery, the comet was low in the south but moving north. By the end of May, observers were finding it difficult to see the 5th magnitude comet because of its low altitude in the twilight. The last sighting of the comet around solar conjunction was in mid-June.
During June, a new orbit was calculated for the comet, and it became apparent that it would be very bright by October of that year.
The comet was recovered from the solar glare on 18th August by Flaugergues himself. Perihelion occurred on 12th September when the comet was just over 1 AU from the Sun. At this time, the comet was nearly 1.6 AU from Earth, and at 5th magnitude. However, during the rest of September and most of October, the comet brightened to better than 1st magnitude, despite its minimum distance from Earth only being a mere 1.1 AU. For Northern Hemisphere observers, the comet was circumpolar in early October, and displayed two easily seen tails. In mid-October, William Herschel noted that the straight gas tail was 24° in length and the curved dust tail was about 7°. He also described the apparent nucleus as having a ruddy hue surrounded by a large coma (28 arc-minutes wide) with a bluish-green tinge.
Naked-eye observations of the comet continued until mid-January, 1812, and incredibly the tail reportedly grew to 70 degrees by December 1811. All up, the comet was visible without optical aid for 260 days, a record that stood head and shoulders above every other comet until Hale-Bopp.
News of new discoveries, and reports on how current comets are performing, can be found in each issue of Comet Tales, available from the writer at 2/100-104 Kissing Point Road, Dundas. NSW. 2117. Annual subscriptions are $10, payable to the writer.