273P/Pons–Gambart

273P/Pons–Gambart, also called Comet Pons-Gambart, is a periodic comet in a retrograde orbit first discovered on June 21, 1827 by Jean-Louis Pons and Jean-Félix Adolphe Gambart. It has a 186 year orbit and it fits the classical definition of a Halley-type comet (20 years < period < 200 years). Its last perihelion was in December 2012 and will next come to perihelion around August 2191.

The orbit was initially considered to be parabolic, but its orbit was recalculated in 1917 and it was found to be elliptical with an orbital period determined to be 64 years with 10 years uncertainly. The comet was considered lost until November 7, 2012, when amateur astronomer Rob Matson discovered a comet in images taken by SWAN instrument on board SOHO, and it was identified that the pre-recovery short-arc orbital calculations for Pons-Gambart were completely wrong because the comet only had a 1-month observation arc with poor data and that was the first perihelion after the 1827 apparition. It was last observed in April 2014 when it was 5.8 AU from the Sun.

The original name when first discovered was C/1827 M1. Before the 2012 return, when Comet Pons–Gambart was speculated to have a roughly 60 year orbit it was suspected of possibly being comet C/1110 K1.

Of the numbered periodic comets only 153P/Ikeya-Zhang has a longer orbital period.