Long-period comet

A comet with an orbital period longer than 200 years. Many follow highly elongated orbits that carry them from the distant Solar System toward the Sun.

Oort cloud: A hypothesized spherical reservoir of icy bodies surrounding the Solar System at great distances. Gravitational disturbances can send its bodies inward as long-period comets.
Solar System formation: The process by which the Sun, planets, and smaller bodies formed from a collapsing cloud of gas and dust. The distant comet reservoirs arose from leftover material scattered during planet formation.
Comet Hale–Bopp: A bright comet discovered in 1995 that reached naked-eye visibility in 1997. Its long orbital period and exceptional visibility made it a landmark modern apparition.
Short-period comet: A comet with an orbital period shorter than 200 years. Its more frequent returns contrast with the long intervals between long-period comet passages.
Cometary orbit: The path a comet follows under gravity, usually an ellipse, parabola, or hyperbola. Orbital shape and period distinguish long-period comets from shorter-period populations.
Oort cloud formation: The proposed assembly of a distant comet reservoir from icy bodies scattered outward by the giant planets. It explains how many long-period comets came to occupy remote, weakly bound orbits.
Comet Hyakutake: A comet discovered in 1996 that passed close to Earth in 1996. Its close approach produced a prominent tail and unusually detailed observations.
Halley-type comet: A short-period comet with an orbital period between 20 and 200 years. Its period places it below the conventional long-period threshold.
Orbital eccentricity: A measure of how much an orbit deviates from a circle. High eccentricity lets a comet travel from the distant Solar System to the Sun.
Nice model: A model of Solar System evolution in which the giant planets migrated from their original orbits. Planetary migration and scattering help explain the emplacement of distant icy bodies.

Linked from 7 pages