Asteroid

Definition: Minor planets, small rocky bodies.
Composition: Leftover material from our solar system.
Largest asteroid: 1 Ceres
Total discovered to date: Over 250,000 designations have been assigned by the Minor Planet Center; over 100,000 have been observed more than once.
Total numbered asteroids to date: Over 30,000.
Near-Earth asteroids: Around 1.0 AU from earth, with perihelia less than or equal to 1.3 AU.

Aten group <><><><><> Innermost, semi-major axis less than 1.0 AU, perihelion greater than 0.983 AU.
Apollo group <><><><><> Semi-major axis greater than 1.0 AU, perihelion less than 1.017 AU.
Amor group <><><><><> Semi-major axis greater than 1.0 AU, perihelion between 1.017 and 1.3 AU.

Main Belt Asteroids: Located between orbits of Mars and Jupiter (1.8 to 4.0 AU) in the "asteroid belt".
Trojan Asteroids: Two groups of asteroids located along the orbital path of Jupiter, 60 degrees ahead and behind the planet.
Centaurs: Asteroids in the outer solar system having orbits between Mars and beyond Neptune.
Type Classification: Based on albedo (reflectivity), and color or spectra. Most common are C, S, and M.
C-type: Very dark (albedo=0.03), flat spectra, grayish in color.
S-type: Moderately bright (albedo=0.10-0.22), spectra with moderate to strong absorption bands, greenish to reddish in color.
M-type: Moderately bright (albedo=0.10-0.18), spectra with few absorption bands, reddish in color.