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.
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.
- "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, (and later additions Uranus and 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 is different from 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" is also very different to minor planet or dwarf planet.
Famous quotes containing the words inferior, superior and/or planets:
“Though of erect nature, man is far above the plants. For man’s superior part, his head, is turned toward the superior part of the world, and his inferior part is turned toward the inferior world; and therefore he is perfectly disposed as to the general situation of his body. Plants have the superior part turned towards the lower world, since their roots correspond to the mouth, and their inferior parts towards the upper world.”
—Thomas Aquinas (c. 1225–1274)
“He said, truly, that the reason why such greatly superior numbers quailed before him was, as one of his prisoners confessed, because they lacked a cause,—a kind of armor which he and his party never lacked. When the time came, few men were found willing to lay down their lives in defense of what they knew to be wrong; they did not like that this should be their last act in this world.”
—Henry David Thoreau (1817–1862)
“Perhaps when distant people on other planets pick up some wave-length of ours all they hear is a continuous scream.”
—Iris Murdoch (b. 1919)