Planets

Myths / Planets

For the ancient Greeks (before the age of telescopes) the night sky was thought to consist of two very similar components: fixed stars, which remained motionless in relation to each other, and “wandering stars” (Ancient Greek: asteres planetai), which moved relative to the fixed stars over the course of the year. Hyginus, in his Astronomica, explains that the Greeks called the five stars that wander planetai (Hyginus, Astronomica 2.42).

The Seven Planets

The five planets visible to the naked eye are Mercury, Venus, Mars, Jupiter and Saturn. The Sun and the Moon were not added to the list at a later date: Plato already counts them with the others. In the Timaeus the sun, the moon and “five other stars, which bear the appellation of planets” were made together to mark the numbers of time, seven bodies set in seven orbits. The Moon is placed in the first circle around the earth, the Sun in the second, and then the Morning Star and the star sacred to Hermes (Plato, Timaeus 38c–d). In the Myth of Er, Plato pictures the heavens as a spindle with eight whorls fitted one inside another, each carrying a circle of the heavens (Plato, Republic 616d–617b).

Planets and Gods

Each wandering star was given to a god. Plato’s Epinomis says that the planets have “received titles of gods”: the Morning Star, which is also the evening star, belongs to Aphrodite, and the star that keeps company with the sun and the Morning Star belongs to Hermes (Plato, Epinomis 987b–c). The Latin names in use today are the Roman names of the gods the Greeks had assigned. The Epinomis also names the three slow planets: the slowest is called the star of Cronus (Saturn), the next slowest the star of Zeus (Jupiter), and the next the star of Ares (Mars), which has the ruddiest colour of all (Plato, Epinomis 987c). Hyginus gives the stars of Jupiter, Mars, Venus and Mercury the names Phaenon, Pyrois, Lucifer or Hesperus, and Stilbon, and says that Mars’ star was given to Heracles by some writers (Hyginus, Astronomica 2.42, 4.16–19). The Greek god and the Roman god behind each planet are:

Mercury, the star of Hermes, called Stilbon in Greek
Venus, the star of Aphrodite, also called Lucifer and Hesperus as the morning and evening star
Mars, the star of Ares, called Pyrois, the ruddiest of the planets
Jupiter, the star of Zeus, called Phaenon by Hyginus
Saturn, the star of Cronus, the slowest of the planets (Plato, Epinomis 987c)

The ancient sources do not agree on every assignment. Hyginus reports that the second star was given to the Sun by some writers and to Saturn by others, and that Eratosthenes named it Phaethon after the son of the Sun; those who gave it to Saturn said it returns to the same sign every thirty years (Hyginus, Astronomica 2.42, 4.18).

After the Telescope

After the invention of the telescope three more planets were identified: Uranus, Neptune and Pluto. Uranus (found in 1781) is named after Ouranos, the Greek god of the sky; Neptune (found in 1846) carries the Roman name of Poseidon, the god of the sea; and Pluto (found in 1930) the Roman name of Hades. Pluto has been classed as a dwarf planet since 2006, so the Solar System now counts eight planets.