C/1861 J1

C/1861 J1 Discovery Discovered by: John TebbuttDiscovery date: 1861 Alternate designations: Great Comet of 1861, 1861 II Orbital characteristics A Epoch: 2400920.5 Aphelion distance: 109 AU Perihelion distance: 0.82 AU Semi-major axis: 55 AU Eccentricity: 0.98507 Orbital period: 408 a Inclination: 85.4° Last perihelion: June 12, 1861Next perihelion: 2269

The Great Comet of 1861 formally designated C/1861 J1 and 1861 II, was a comet that was visible to the naked eye for approximately 3 months. It was categorized as a Great Comet, one of eight in the 19th century.

It was discovered by John Tebbutt of Windsor, New South Wales, Australia, on May 13, 1861, with an apparent magnitude of +4, a month before perihelion (June 11). It was not visible in the northern hemisphere until June 29, but it arrived before word of the comet's discovery.

The comet of 1861 interacted with the Earth in an almost unprecedented way. For two days, when the comet was at its closest (0.1326 AU), the Earth was actually within the comet's tail, and streams of cometary material converging towards the distant nucleus could be seen. By day also the comet's gas and dust even obscured the Sun.

By the middle of August the comet was no longer visible to the naked eye, but it was visible in telescopes until May 1862. An elliptical orbit with a period of about 400 years was calculated, which would indicate a previous appearance about the middle of the 15th century, and a return in the 23rd century.

As of 1992 this Great Comet had traveled more than 100 AU from the Sun, making it even further away than dwarf planet Eris. It will come to aphelion around 2063.