20D/Westphal

20D/Westphal was a periodic comet with an orbital period of 61 years. It fits the classical definition of a Halley-type comet (20 years < period < 200 years).^[3] The comet appeared to disintergrate during the 1913 apparition and hasn't been observed since then.^[4]

20D/Westphal

Discovery
Discovered by	J. G. Westphal
Discovery date	July 24, 1852
Designations
Alternative designations	21P/1852 O1; 1852 IV; 21P/1913 S1; 1913 VI; 1913d
Orbital characteristics
Epoch	1913-11-09 (JD 2420080.5)
Aphelion	30.030 AU
Perihelion	1.2540 AU
Semi-major axis	15.642 AU
Eccentricity	0.9198
Orbital period	61.87 yr
Inclination	40.890°
Last perihelion	January 3, 1976?[1] (unobserved)
Next perihelion	May 4, 2038?[2][1] (lost since 1913)

The comet was originally discovered by the German astronomer J. G. Westphal (Göttingen, Germany) on July 24, 1852. It was independently discovered by the American astronomer Christian Heinrich Friedrich Peters (Constantinople) on August 9. The comet exhibited many flunctuations in intristic brightness and reached an apparent magnitude of around 4 while a dust tail was also observed.^[4] It was last observed about 120 days after perihelion.^[4]

The comet was recovered on September 27, 1913, by Pablo T. Delavan (La Plata Astronomical Observatory), about 60 days before perihelion, however the comet faded as it approached the Sun, losing its central condesation and the nucleus became elongated.^[4] The plates of the comet indicate that the disintergration began on October 1, when the comet was reported to be visible with naked eye using averted vision.^[4] It was last observed on November 26, 1913. It was predicted to return in 1976^[1] but was never observed, and is now considered a lost comet.