Planets
Planets
Mercury | Venus | Earth | Mars | Jupiter | Saturn | Uranus | Neptune |* Pluto
Traditional Definition
Etymology: Middle English planete, from Old French, from Late Latin planeta, modification of Greek planEt-, planEs, literally, wanderer, from planasthai to wander.
any of the seven celestial bodies: Sun, Moon, Venus, Jupiter, Mars, Mercury, and Saturn that in ancient belief have motions of their own among the fixed stars.
any of the large bodies that revolve around the Sun in the solar system.
[see IAU resolutions below]
a similar body associated with another star.
EARTH -- usually used with "the".
a celestial body held to influence the fate of human beings
a person or thing of great importance : LUMINARY
- plan�et�like /-"lIk/ adjective
* The IAU [ International Astronomical Union ]     officially designates planets within our solar system.
STATUS February 2, 2006
"The IAU notes the very rapid pace of discovery of bodies within the Solar system over the last decade and so our understanding of the Trans-Neptunian Region is therefore still evolving very rapidly.   This is in serious contrast to the situation when Pluto was discovered. As a consequence, The IAU has established a Working Group to consider the definition of a minimum size for a Planet. Until the report of this Working Group is received, all objects discovered at a distance from the Sun greater than 40 AU will continue to be regarded as part of the Trans-Neptunian population."
UPDATE August 24, 2006
RESOLUTION 5A
The IAU therefore resolves that planets and other bodies in our Solar System be defined into three       distinct categories in the following way:
(1) A planet1 is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a        hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighbourhood around its orbit.
(2) A dwarf planet is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass       for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium        (nearly round) shape2,
(c) has not cleared the neighbourhood around its orbit, and
(d) is not a satellite.
(3) All other objects3 orbiting the Sun shall be referred to collectively as       "Small Solar System Bodies".
1The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2An IAU process will be established to assign borderline objects into either       dwarf planet and other categories.
3These currently include most of the Solar System asteroids, most Trans-Neptunian       Objects (TNOs), comets, and other small bodies.
Relative sizes of the planets and stars by Dave Jarvis .
Smallest Planets