Editor's Update (Nov. 27): Comet ISON is just one day away from its close encounter with the sun on Thanksgiving Day (Nov. 28). The comet will be just 684,000 miles (1.1 million kilometers) from the sun's surface when it makes its close approach. It is still uncertain if the comet will survive the encounter. If it does survive, the comet could once more be visible to the unaided eye in early December. Latest Story: Comet ISON's Thursday Sun Encounter a Thanksgiving Feast for NASA
Named after the International Scientific Optical Network, Comet ISON — officially designated "C/2012 S1 (ISON) — has the potential to be the most spectacular comet of the century. But it could also prove to be a dud. A critical moment will be perihelion passage, when the comet comes closest to the sun.
On Nov. 28, 2013, the head of the comet passes 800,000 miles (1.2 million kilometers) above the sun's surface. This is closer to the sun's surface than the sun's own diameter. [Will Comet ISON Sizzle or Fizzle? (Video)]
If it survives its close brush with the sun without breaking up, Comet ISON will make a hairpin turn past the sun, whipping around onto the outbound leg of its orbit. The comet could provide a spectacular display in Earth’s skies in November and December.
Comet ISON Seen By NASA Spacecraft | Video
Astronomers have high hopes because Comet ISON seems to be a new comet fresh from the Oort cloud, a zone of deep-frozen objects orbiting in the dark outlands of our solar system. The most optimistic prediction is that Comet ISON could rival the Great Comet of 1680. [Photos of Comet ISON]
The performance of comets cannot be accurately predicted. Some previous "great comets" such as Comet Elenin in 2011, fizzled instead.
Comet ISON is believed to be making its first trip to the sun, and so is hoped to still have most of its volatiles intact. Volatiles are the substances which heat up and blast off the comet's nucleus to form the wispy comet tail which can stretch for millions of miles through space.
Editor's note: If you have an amazing picture of Comet ISON or any other night sky view that you'd like to share for a possible story or image gallery, send photos, comments and your name and location to managing editor Tariq Malik at spacephotos@space.com.
- Will Comet ISON be Comet of the Century?
- Amazing Comet Photos of 2013 by Stargazers
- Comets: Formation, Discovery and Exploration
- Photos: Spectacular Comet Views from Earth and Space
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