The best-known periodic comet, returning to perihelion at average intervals of 76 years on a retrograde orbit (the time between returns ranges from 74 to 79 years). Comet Halley has been observed at every return since 240 bc. It is named after E. Halley, who in 1705 showed that comets seen in 1531, 1607, and 1682 were identical, and successfully predicted the return of 1758. In 1910 Halley’s Comet passed 0.15 au from Earth, reaching magnitude 0 and showing a 100° tail; the Earth passed through the tail on May 20. At its most recent return, in 1986 (perihelion February 9, closest to Earth 0.42 au on April 11), it reached 3rd magnitude and had a 10° tail. On this occasion, five space probes were sent to investigate it: Giotto, Sakigake, Suisei, and Vega 1 and 2. It was found to have an irregular nucleus measuring 15 × 8 km with an albedo of 0.04. Halley’s Comet is the parent of the Eta Aquariid and Orionid meteor showers. Its perihelion is 0.586 au, aphelion 35.1 au, eccentricity 0.967, inclination 162°.3. The comet will next return to perihelion in 2061 July.

http://cometography.com/pcomets/001p.html Information page at Cometography website.