Comet ISON entered the inner solar system at a relatively shallow angle above the orbits of the planets, and then it left the inner solar system at a much steeper angle above the ecliptic. ISON spent approximately four months closer to the sun than the orbit of Mars. From early October to early December 2013, the comet moved toward the sun before leaving the inner solar system.
ISON came within 800,000 miles of the surface of the sun, which is less than the sun's own diameter. Remnants of ISON left the inner solar system in early February 2014. These remnants were less luminous than the whole comet before it encountered the sun.
ISON was dubbed the "comet of the century" as it approached the inner planets from the Oort Cloud. The object was discovered in September 2012 by two Russian astronomers when it was still beyond the orbit of Jupiter. Several satellites observed ISON as it entered the area of the inner planets, swung around the sun and disappeared for a few days before emerging as comet fragments.
If ISON had survived its trip around the sun intact, scientists felt the object would have been one of the brightest comets ever observed. Despite its lack of luster to Earth-based skywatchers, ISON provided scientists with more than a year's worth of data on how far-reaching comets enter the solar system and then break apart after a closer encounter with the sun.