35P/Herschel–Rigollet

Observational history

1789 apparition

Caroline Herschel first observed the comet on 21 December 1788 and it was observed later that night by her brother William Herschel who described it as looking like a bright nebula and about 5–6 minutes in diameter, and much larger than the planetary nebula, Messier 57.

Through December and January the comet was observed by Nevil Maskelyne at the Greenwich Observatory and by Charles Messier at the Paris Observatory. Maskelyne was the last observer of the comet, his final observation taking place on 5 February 1789.

Similar possible orbits for the comet were calculated in 1789 by Pierre Méchain and in 1922 by Margaretta Palmer. Palmer considered that the orbit which best fitted the observations was an elliptical one with a period of 1,066 years.

1939 apparition

Roger Rigollet rediscovered the comet on 28 July 1939; it was described as diffuse and with a magnitude of 8.0. The sighting was confirmed the next day by Alfonso Fresa of the Observatory of Turin (Italy) and George van Biesbroeck of the Yerkes Observatory. The comet steadily faded after August, final (photographic) observations being obtained on 16 January 1940. The comet was also extensively observed from the Incheon Meteorological Observatory between July and September 1939. W. H. Dirk captured a series of photographic plates of the comet alongside recording its positions from August to September 1939.

Following the 1939 rediscovery, the comet's orbit was calculated by Jens P. Möller (Copenhagen, Denmark), and Katherine P. Kaster and Thomas Bartlett (Berkeley, USA). A perihelion date of 9 August 1939 was indicated. Based on these early orbits, Leland E. Cunningham of the Harvard College Observatory suggested that the comet was likely identical with Herschel's Comet of 1788.

The final calculation of the orbit, by Brian G. Marsden in 1974, used 75 positions from both apparitions of the comet in 1788 and 1939–40 in addition to perturbations by planets, and linked the two sightings, with a perihelion date of 9 August 1939 and a period of 155 years.

Closest approaches to Earth

• 4 November 1788 – 0.80 AU
• 30 July 1939 – 0.82 AU

References

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Bibliography

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