How Did the Planets Get Their Names?

When you gaze up at the night sky while Venus, Mars and Jupiter are reflecting brightly, or see pictures of the planets that inhabit our solar system, you might ponder that their names sound ancient, powerful, or even mysterious. Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and (dwarf planet) Pluto. Where did these names come from? Who chose them, and what do they mean? To find out, we need to take a trip back in time – venturing into the eras of ancient civilizations, mythologies, and the early history of astronomy.

The Planets and the Ancient Night Sky

Before telescopes, people could only see five planets with the naked eye: Mercury, Venus, Mars, Jupiter, and Saturn. The word planet comes from the ancient Greek word planētēs, meaning “wanderer,” because planets move against the background of fixed stars. (As an aside, that’s because they’re closer to us and their orbits around the sun are therefore noticeable, compared to the relative movements of much more distant bodies.)

Ancient astronomers in places like Babylonia, Greece, Rome, and Egypt watched the movements of these bright wanderers and gave them special importance. Different cultures gave the planets different names, but the ones we use today mostly come from the Romans, who named the planets after their most important gods and goddesses.

The Five Naked-Eye Planets: Roman Gods and Goddesses

1. Mercury
Mercury is the fastest-moving planet across our sky. The Romans named it after Mercury, the swift messenger god who wore winged sandals and delivered messages for the other gods. The Greeks called this planet Hermes.

2. Venus
Venus shines the brightest and is often called the “morning star” or “evening star.” The Romans named it Venus, after their goddess of love and beauty. The Greeks called her Aphrodite.

3. Mars
Mars is reddish in the night sky, which reminded ancient people of blood. The Romans named it Mars, their god of war. The Greeks called him Ares.

4. Jupiter
Jupiter is the biggest and brightest of the planets. The Romans named it Jupiter, after their king of the gods – the most powerful deity. The Greeks called him Zeus.

5. Saturn
Saturn moves slowly across the sky. The Romans named it Saturn, after their god of agriculture and time, who was the father of Jupiter. The Greeks called him Cronos.

The Outer Planets: Discovered by Telescope

The planets beyond Saturn – Uranus, Neptune, and the dwarf planet Pluto – are too faint to see without telescopes. They were discovered much later, so their naming stories are a bit different.

6. Uranus
Discovered in 1781 by William Herschel, Uranus was at first simply called “George’s Star” after King George III of England! But many astronomers wanted to follow the tradition of using names from mythology. That’s fortunate, as a planet isn’t a star, so the name wasn’t particularly apt for a number of reasons. The name Uranus was suggested, after the Greek god of the sky (Ouranos), who was the father of Cronos (Saturn) and grandfather of Zeus (Jupiter). This kept the “family” in order, at least according to Greek myths!

7. Neptune
Neptune was discovered in 1846. Its beautiful blue color made astronomers think of water, so it was named after Neptune, the Roman god of the sea. The Greek equivalent is Poseidon.

8. Pluto
Pluto was discovered in 1930 by Clyde Tombaugh. Because it was far from the Sun and very dark and cold, it was named after Pluto, the Roman god of the underworld (Greek name: Hades). An 11-year-old girl in England, Venetia Burney, suggested the name – and it quickly caught on worldwide. Contrary to popular belief, it wasn’t named after a friendly cartoon dog from the Disney animation line-up. 🙂

So, What About Earth?

Unlike the other planets, Earth doesn’t have a name from Roman or Greek mythology. Our word “Earth” comes from Old English and German words (“eorthe” and “erde”) that mean “ground” or “soil.” In Latin, Earth was sometimes called Terra or Tellus – and you might see these names in science or literature. The name “Earth” reflects the fact that, for a long time, people didn’t realize our planet was a planet just like the others! Early humans presumed that the planets, sun and stars moved around or over our sky, without considering that we might be a similarly round planetary mass moving through space in concert with the other players that make up the solar system.

Honoring Mythology and Tradition

Why did people use names from mythology?
For ancient peoples, the night sky was full of mysteries and stories. Naming planets after gods and goddesses helped explain their motions and their “personalities.” For example, Mars (the red planet) seemed fierce, like the god of war, so an alignment with that deity made sense.

The tradition stuck, and even as we discovered new planets and moons, astronomers continued using names from ancient myths. Today, scientists still use mythological names for newly discovered objects in our solar system; and even for features on other planets, like craters or volcanoes.

Beyond the Eight: Dwarf Planets and More

Pluto was reclassified as a dwarf planet in 2006, but its mythological name remains. Other dwarf planets (like Eris, Haumea, and Makemake) are also named after gods and goddesses from different cultures around the world. Eris is a Greek name – representing the goddess of discord and strife. Haumea comes from Hawaiian tradition; a goddess of fertility. Makemake draws its name from the creator god of the Rapa Nui people, who lived on Easter Island.

Fascinating Facts About Planet Names

• Days of the week: In many languages, some of the days of the week are named after the planets and their gods – like “Martes” (Tuesday), which is Mars in Spanish.

• Moons, too: Most moons are also named after mythological characters – Jupiter’s moons are named after his lovers and friends!

• No Roman name for Earth: “Earth” is the only planet not named after a Greek or Roman deity.

• Venetia Burney: An 11-year-old suggested the name Pluto, and she lived to see its reclassification as a dwarf planet! That would have been a bittersweet moment, no doubt, but Pluto’s legacy and her role in its naming will forever live on.

• Naming committees: Today, the International Astronomical Union (IAU) oversees the official naming of planets and other space objects.

Questions to Ponder

1. Why do you think ancient people connected planets with gods and goddesses?

2. If you discovered a new planet, what name would you give it, and why?

3. How do you think the names of planets influence how we imagine or study them today?

4. Are there other objects in the solar system (like moons or asteroids) with interesting naming stories?

5. How might naming conventions change as we discover more planets around other stars (exoplanets)?

The story of how the planets got their names is a mix of science, myth, and human curiosity; a tradition that continues as we explore new worlds in our universe!