|Discovered by||J. G. Westphal|
|Discovery date||July 24, 1852|
|21P/1852 O1; 1852 IV;|
21P/1913 S1; 1913 VI;
|Orbital characteristics A|
|Epoch||1913-11-09 (JD 2420080.5)|
|Semi-major axis||15.642 AU|
|Orbital period||61.87 yr|
|Last perihelion||January 3, 1976 (unobserved)|
|Next perihelion||May 4, 2038|
(lost since 1913)
20D/Westphal was a periodic comet with an orbital period of 61 years. It fits the classical definition of a Halley-type comet with (20 years < period < 200 years). It 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 was last seen between September 27 and November 26, 1913, first by Pablo T. Delavan (La Plata Astronomical Observatory) and then others. It was predicted to return in 1976 but was never observed, and is now considered a lost comet.