Post by Chicago Astronomer - Astro Joe on Aug 20, 2006 2:06:28 GMT -6
IAU Planet Definitions
Planets -
Under the proposed definition, two conditions must be satisfied for an object to be called a "planet."
1. Must be in orbit around a star, while not being itself a star.
2. Must be massive enough for its own gravity to pull it into a nearly spherical shape.
NEW PLANET CATEGORY -
A pluton is a new category of planet now being defined by the IAU. To be a pluton, a body:
1. Must satisfy the technical definition of planet.
2. Resides in orbit around the sun that takes longer than 200 years to complete (i.e., orbits beyond Neptune).
3. Typically has an orbit that is highly tilted with respect to the classical planets and is far from being perfectly circular.
NON-IAU DESCRIPTIVE DEFINITIONS
Classical planet
The eight largest planets, discovered by sky watchers and astronomers starting from the beginning of human history until the year A.D. 1900. Example: Venus
Dwarf planet
Generally used to describe any planet that is smaller than Mercury.
Ceres would be an example.
Source: International Astronomical Union (IAU)
