How do you honor the beguiling beauty of a twinkling celestial orb? Give it the name of a god. How do you honor a god? Name one of the sky’s bewitching wonders after him. And thus, the ancients named the sky’s brightest planets after members of the mythological pantheon, affording the highest recognition to both gods and planets. As new planets were discovered, the tradition was continued.
While many of the planets had other names before the Romans bestowed them with their divine namesakes — it's these names that are recognized by the International Astronomical Union (IAU). The IAU is the body officially recognized by international astronomers and scientists as the de facto naming authority for astronomical bodies. (Although plenty of other cultures have their own names for the planets, too.)
But why did certain gods get assigned to certain heavenly bodies? Here are the celestial back stories.
The earliest recorded sightings of Mercury are from the Mul-Apin tablets from the 14th century B.C., in which Mercury was described in a jumble of cuneiform as “the jumping planet.” By the 1st millennium B.C., the Babylonians were calling the planet Nabu after their god of writing and destiny. The ancient Greeks called Mercury Stilbon, meaning “gleaming,” while later Greeks called it Hermes after the fleet-of-foot messenger to the gods because the planet moves so swiftly across the sky. In fact, Mercury speeds around the sun every 88 days, traveling through space at nearly 31 miles per second faster than any other planet. It's a speedy thing! The Romans took the helm from the Greeks and named the planet, Mercury — Hermes' Roman counterpart.
Although the Venusian atmosphere offers a scorched world so hot it can melt lead and has a surface pressure 90 times that of our planet, it’s an undeniably beautiful vision to behold from the comfort of Earth. Because of Venus’ proximity and the dense cloud cover that reflects the sunlight, it is the third brightest natural object in the sky (after the sun and moon). It is so bright it can cast shadows! Its brightness and morning appearance inspired the ancient Romans to associate the pulchritudinous planet with Venus, the goddess of love and beauty. Other civilizations have named it for their god or goddess of love as well.
Poor Earth. While all the other planets were exalted with names of gods and goddesses, Earth's name comes from a plain old Anglo-Saxon word which simply means “ground.” Not very glamorous for a planet that has been so bounteous with life and has been such a welcoming hostess, but it’s understandable. Earth wasn’t considered a planet for much of human history. Given our early terrestrial perspective, it was thought that Earth was the central object around which the rest of the celestial bodies revolved. It wasn't until the 17th century that astronomers realized that it was the sun at the center of things — oops. By that time, renaming the "new" planet was likely not even a consideration.
In the ancient Roman pantheon, the god Mars was second in importance only to Jupiter. While not much is known of his genesis, in Roman times he had developed into a god of war. He was considered a protector of Rome, a nation that took great pride in its military. So what to call the mighty blood-red planet in the sky? Mars, of course. The oxidized iron in the planet’s soil along with its dusty atmosphere give Mars a red tinge that has led to other hue-inspired appellations as well, like the Red Planet, or the Egyptian name for the fourth planet, "Her Desher,” meaning the red one.
The largest planet in our solar system — so large it forms its own ersatz solar system — was named Zeus by the Greeks and Jupiter (Zeus’s Roman counterpart) by the Romans. Jupiter was the god of light and the sky, and the most important of all gods in the Roman pantheon. This dynamic gas giant is made up of more that twice the material of the other bodies orbiting the sun combined and has 67 moons of its own. It's no wonder it was named after Rome's official chief deity.
Hooped by its thousands of beautiful ringlets, Saturn is unique among the planets with its spectacular and complicated system of circles. It has been known since prehistoric times and was the most distant of planets observed. As such, Saturn has been bestowed with much reverence in a number of cultures. The ancient Greeks made the sixth planet sacred to Cronus, the god of agriculture and time. Because Saturn had the longest observable repeatable period in the sky, it was thought to be the keeper of time. The Romans named it Saturn — the father of Jupiter and the Roman counterpart to Cronus.
While Uranus had been observed but recorded as a fixed star since prehistory, it was Sir William Herschel who discovered is as a planet in 1781. He named it Georgium Sidus (George’s star) after King George III, saying, “In the present more philosophical era, it would hardly be allowable to have recourse to the same method [as the ancients] and call it Juno, Pallas, Apollo or Minerva, for a name to our new heavenly body.” The new name lacked popularity outside of Britain. Johann Elert Bode’s suggestion of Uranus, the father of Saturn and god of the sky, became widely used and the standard in 1850 when the HM Nautical Almanac Office officially accepted the new name instead of Georgium Sidus.
Neptune was the first planet discovered by math rather than observation. It was "predicted" by John Couch Adams and Urbain Le Verrier, who accounted for the irregularities in the motion of Uranus by correctly guessing that another planet was the cause. Based on those predictions, Johann Galle found the planet in 1846. Galle and Le Verrier wanted to name the planet for Le Verrier, but this was not acceptable to the international astronomical community. Janus and Oceanus were proposed, but ultimately it was Le Verrier’s suggestion of Neptune, the god of the sea, that became the internationally accepted moniker. This was fitting given the planet’s methane-induced, rich blue tint.
Whether you are a Pluto-as-a-planet proponent or denier, we couldn’t leave our favorite dwarf planet out of the mix. To many of us, Pluto will always be a real planet. (So there.) Pluto was discovered at the Lowell Observatory in Flagstaff, Arizona, in 1930 after predictions of its existence fueled Percival Lowell to pursue its discovery. It wasn’t until 14 years after Lowell's death that the new object was discovered, an event that made headlines around the world. The observatory received more than 1,000 name suggestions from across the globe. The winning name was suggested by an 11-year-old school girl in England who loved classical mythology. Appropriately, it took decades to find the planet that was known to be out there; it was invisible, as was Pluto, the god of the underworld. Another nudge in its favor to win the final vote was that the first two letters of Pluto are the initials of Percival Lowell.
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