Inferior and superior planets the orbit of Earth. These terms were originally used in the geocentric cosmology of Claudius Ptolemy to differentiate as inferior those planets (Mercury and Venus) whose epicycle remained co-linear with the Earth and Sun, and as superior those 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. When Earth is stated or assumed to be the reference point: The terms are sometimes used more generally; for example, Earth is an inferior planet relative to Mars.
Science and technology of the Han dynasty Han astronomers believed the Sun, Moon, and planets were spherical like balls or crossbow bullets. He also wrote that the Moon and planets produce no light of their own, are viewable to people on Earth only because they are illuminated by the Sun, and those parts not illuminated by the Sun would be dark on the other side. For this, Jing compared the Moon to a mirror illuminating light. In the 2nd century CE, Zhang Heng drew a similar comparison to Jing's by stating that the Sun is like fire and the Moon and planets are like water, since fire