In ancient Greece, the distinction between planets and stars was largely based on observation and the movement of celestial objects. Here’s how they differentiated between the two:
- Planets (from the Greek word planētēs, meaning “wanderer”):
- The Greeks noticed that certain points of light in the night sky moved against the background of fixed stars. These objects were different from the stars because they didn’t remain in the same position relative to the stars.
- The planets, such as Mercury, Venus, Mars, Jupiter, and Saturn, appeared to wander through the constellations over time. Their motion was more complex than the predictable movement of the stars, and they would sometimes change direction, moving retrograde (backward) for periods before resuming their forward motion.
- These wandering stars were thus recognized as a separate category, termed “planets.”
- Stars:
- The stars were fixed points of light that did not change their position relative to one another. They formed patterns or constellations that were consistent throughout the year.
- The Greeks believed that stars were part of a celestial sphere, fixed in place, and moving in a predictable manner with the rotation of the heavens.
While the ancient Greeks didn’t have our modern understanding of what planets and stars are, their careful observations of celestial movement led them to this distinction. They attributed different properties to each type of object in the sky, with planets being seen as “wanderers” and stars as part of a fixed celestial order.