A periodic comet, the parent of the Perseid meteor shower, independently discovered in 1862 July by the American astronomers Lewis Swift (1820–1913) and Horace Parnell Tuttle (1837–1923). It reached magnitude +2 and showed a tail 25–30° long in 1862 August. Swift–Tuttle’s nucleus was particularly active, with many jets or fountains of material. Such activity is the source of non-gravitational forces which influence the comet’s orbital period. It was recovered in 1992 September, reaching perihelion (0.96 au) on December 12 and peaking at 5th magnitude. The comet has an average orbital period of about 130 years. It is now known to be identical with Comet Kegler of 1737, and appearances back to 69 bc have been identified. Comet Swift–Tuttle will make a close passage to Earth on its next return in 2126. Its orbit has an eccentricity of 0.963, aphelion 51.2 au, and inclination 113°.5. The nucleus has an estimated diameter of around 25 km.

http://cometography.com/pcomets/109p.html Information page at Cometography website.