(astronomy) Of, or relating to planets, or the orbital motion of planets. / Of, or relating to the Earth; terrestrial. / Of, or relating to the whole Earth; global. / (of a gear train) epicyclic

A planetary nebula.

A display museum in which images of stars and other astronomical phenomena are projected onto a domed ceiling. / An orrery.

plural of planetarium

plural of planetarium

An assembly of meshed gears consisting of a central (sun) gear, a coaxial internal gear-wheel and one or more intermediate pinions supported on a revolving carrier.

(astronomy) The study of planets, planetary systems and the solar system.

(astronomy) Any of many small, solid astronomical objects that orbit a star and form protoplanets through mutual gravitational attraction.

(astronomy) Being or relating to one of these astronomical objects.

plural of planetesimal