The ancient Greeks saw the five visible planets and called them “wandering stars” because they moved randomly across the sky instead of staying in fixed positions like the stars. The word “planet” comes from the Greek word for “wanderer.”
We have known for many centuries that the planets are not stars. They appear to wander because they orbit the Sun, just like our planet Earth. They orbit at different speeds, making them appear to wander in the sky. For astronomers to classify a celestial body as a planet, it must meet three requirements:
- It must have enough mass for gravity to cause it to become spherical, unlike an asteroid.
- It must not have enough mass to cause thermonuclear fusion, which would make it a star.
- It must have cleared the area of debris known as planetesimals.
We have five planets that are visible without the aid of telescopes or even binoculars. Two of the visible planets are called inferior planets, not because of importance but because their orbit is inside Earth’s orbit. They are Mercury and Venus. The other three are known as the superior planets since they are beyond Earth’s orbit. They are Mars, Jupiter, and Saturn.
There is one essential thing the ancient Greeks did not understand about the solar system. They did not know that it is orderly. The Greeks saw a pantheon of gods controlling various aspects of the Earth and skies. Each of their gods had all of the bad traits of humans struggling with each other. It was the Judeo-Christian concept of one almighty and wise creator God who created an orderly system that led to the scientific understanding of the cosmos.
Today, we can study and understand the wisdom of God in creation. Because of that, we can know where the planets and stars, as well as solar and lunar eclipses, will be visible at any given time and from any location on Earth. Those “wandering stars” are not wandering after all.
— Roland Earnst © 2020