Inferior and superior planets

The terms "inferior planet" and "superior planet" were originally used in the geocentric cosmology of Claudius Ptolemy to differentiate as 'inferior' those planets (Mercury and Venus) whose epicycle remained collinear with the Earth and Sun, compared to the 'superior' planets (Mars, Jupiter, and Saturn) that did not.^[1]

In the 16th century, the terms were modified by Copernicus, who rejected Ptolemy's geocentric model, to distinguish a planet's orbit's size in relation to the Earth's.^[2]

"Inferior planet" is used in reference to Mercury and Venus, which are closer to the Sun than the Earth is.

"Superior planet" is used in reference to Mars, Jupiter, Saturn, Uranus, Neptune, which are farther from the Sun than the Earth is.

The terms are sometimes used more generally: for instance, the Earth is an inferior planet as seen from Mars.

This classification should not be confused with the terms inner and outer planet, which designate those planets which lie inside the asteroid belt and those that lie outside it, respectively. "Inferior planet" should also not be confused with the very different minor planet or dwarf planet.

References

^ Lakatos, Imre; Worrall, John; Currie, Gregory (1980). Worrall, John; Currie, Gregory. ed. The Methodology of Scientific Research Programmes. Cambridge University Press. p. 186. ISBN 0521280311.
^ Kuhn, Thomas S. (1985). The Copernican Revolution: Planetary Astronomy in the Development of Western Thought (4th ed.). Harvard University Press. p. 172. ISBN 0674171039.