Terminology
Units of Measurement
au - Astronomical Units. Approximately the average distance between the earth and the sun
aphelion distance - distance between an object’s orbit point farthest from the sun
perihilion distance - distance between an object’s orbit point closest to the sun
semi-major axes - an object’s mean distance from the sun
Abbreviations
NEO - Near Earth Object. Asteroids or comets with a perihelion distance less than or equal to 1.3 astronomical units
NEA - Near Earth Asteroid
NEC - Near Earth Comet
PHA - Potentially Hazardous Asteroids. Asteroids with the potential to make close approaches to earth. PHAs are classified based on their minimum orbit intersection distance and absolute magnitude.
Earth, Moon, and Asteroid Bennu
Picture of the earth and moon (bottom left) and Asteroid Bennu (top right). Asteroid Bennu is a main-belt asteroid whose orbit is between Mars and Jupiter.
NEA classifications
Amor - An asteroid whose orbit is outside of Earth’s orbit (but within Mars’). Named after asteroid 1221 Amor.
Apollo - An asteroid whose orbit crosses earth’s orbit and whose average distance from the sun is larger than Earth’s. Named after asteroid 1862 Apollo.
Aten - An asteroid whose orbit crosses earth’s orbit and whose average distance from the sun is smaller than Earth’s. Named after asteroid 2062 Aten.
Atira - Also known as an Interior-Earth Asteroid (IEA). An asteroid whose orbit is within the earth’s orbit. Named after asteroid 163693 Atira
