How did the Planets get their Names?

The origin of Western names for the planets

In Ancient Greece the planets were not named directly for gods.  Rather they were given names broadly representing their characteristics. Each planet was also assigned as sacred to a particular god, again often based on characteristics.

Stilbon, or “the gleamer”, was the fastest planet across the night sky, so was assigned to Hermes, the messenger of the gods. Phosphoros, “the light bringer”, was the name for the brightest planet, assigned to Aphrodite, the goddess of love. Pyroeis, “the fiery”, named for its gentle red hue, was ruled over by Ares, the god of war. Phaethon, “the bright”, was assigned to Zeus, the king of the Olympian gods. And finally Phainon, “the shiner,” as the slowest or most stately planet across the sky, was sacred to Cronus, the leader of the Titan gods and father of Zeus.

The Romans, influenced by Greek traditions and learning, took the Greek gods associated with each planet and gave those planets the names of the equivalent gods in their own pantheon – Mercurius, Venus, Mars, Iuppiter, and Saturnus. These names subsequently made their way, with only minor variations, into most modern European languages.

The invention of the telescope in the early 17th century paved the way for the discovery of more distant, fainter planets and the convention of using names of ancient gods was continued. The seventh planet, discovered in 1781, was eventually named after the Greek god of the sky, Ouranos. Just as Cronus (Saturnus) was the father of Zeus (Iuppiter), so Ouranos was the father of Cronus. It’s thought that the Greek name was adopted in error, with the assumption that the Latinised form Uranus would be the Roman version, although the equivalent Roman god is actually Caelus. In subsequent centuries, Neptune, the Roman god of the sea, was adopted for the eighth planet, and Pluto, the Roman god of the underworld, for what was then considered the ninth.

Planet names in some other traditional cultures

The two approaches seen above, of naming planets in honour of gods or to be broadly descriptive, are replicated in many other cultures.

For example, traditional Hebrew astronomy took an approach much like that of Ancient Greece, with the planets’ names being descriptive, or representative of that planet’s supposed influence in the culture.  Mercury is known as Kokhav, simply “the planet” intended to represent a blank slate allowing adaptability. Venus is Nogah, “the bright one”, and Mars Ma’dim, “the red one”.  Jupiter’s name, Tzedek, means “righteousness” or “justice”, with the planet thought to embody the divine. Saturn is named Shabtay, meaning “of the Sabbath”, interestingly tying in with the naming of Saturday in Western cultures.  The approach also extends to the Sun – Khamma, or “the hot one” and the Moon – Levana, or “the white one”.

Traditional Persian naming is an example of a system honouring local gods, generally tying in with the equivalent Greek and Roman gods.  This gives us Tir for Mercury, Nahid for Venus, Bahram for Mars, and Hormoz for Jupiter. Saturn, however, is named differently, its name Keyvan coming from the ancient language of Akkadian. The name means “steady”, as in the Ancient Greek system, acknowledging its slow movement across the sky. When Uranus, Neptune and Pluto were discovered, modern Persian borrowed those words almost precisely from the Western names.