planetāˈrium noun (pl planetāˈria)

1. A machine showing the motions and orbits of the planets, often by the projecting of their images onto a (domed) ceiling
2. A hall or building containing such a machine

planˈetary adjective

1. Relating to the planets or a planet, or this planet
2. Consisting of or produced by planets
3. Under the influence of a planet (astrology)
4. Erratic
5. Revolving in an orbit

planetesˈimal noun

In one theory of the origin of the solar system, any of many very small units absorbed into the planets as these formed

planetic /plən-etˈik/ or planetˈical adjective

planˈetoid noun

1. An asteroid
2. An artificial body put into orbit

planetoiˈdal adjective

planetolˈogist noun

planetolˈogy noun

The science of the planets

planetary gear noun

A gearwheel that travels around a central gearwheel

planetary nebula noun

A ring-shaped nebula around a star, consisting of a shell of gas, illuminated by the star's short-wave radiation

planˈet-strickˈen or planˈet-struck adjective (astrology)

1. Affected by the influence of the planets, esp adversely
2. Blasted

inferior planets

The planets within the earth's orbit (Mercury and Venus)

minor planet

A rocky object that orbits the sun but is smaller than a planet

on another planet (informal)

Not in touch with reality

superior planets

The planets outside the earth's orbit