inferior planet

7.6

A planet that orbits closer to the Sun than Earth, like Mercury or Venus

noun
/ɪnˈfɪriər ˈplænɪt/

Specialized

: planeta inferior

Venus, being an inferior planet, exhibits phases similar to the Moon when viewed from Earth.

Examples

Observations of an inferior planet can only be made during certain times, such as at dawn or dusk.
Mercury is an inferior planet, as its orbit is closer to the Sun than Earth's.
Mercury is an inferior planet.
Venus is also classified as an inferior planet.
Mercury is an inferior planet, as its orbit is closer to the Sun than Earth's.
Venus, being an inferior planet, exhibits phases similar to the Moon when viewed from Earth.
Observations of an inferior planet can only be made during certain times, such as at dawn or dusk.

Surface Forms

inferior planet singular

inferior planets plural

Morphology

inferior + planet

The phrase is compositionally transparent in that 'inferior' modifies 'planet' to signal a relative position, but the specific technical meaning — a planet whose orbit lies inside Earth's (Mercury or Venus) — is an astronomy-specific use of 'inferior' that a B1 learner would not reliably infer from everyday meanings (e.g. 'lower in quality' or 'below'). Because the relation to the constituents is partly clear (a relative/positional sense) but requires domain knowledge of orbital terminology, it is best classified as semi-transparent.

Etymology

Inferior planet comes from old sky-watchers who used inferior to mean 'closer to the Sun' rather than 'worse' because Mercury and Venus travel in paths that are 'inside Earth's orbit', so inferior planet means a planet whose orbit lies inside Earth's.