Planets

Definition

Planets are celestial bodies that orbit a star, such as the Sun, and have cleared their orbit of other debris. They do not produce their own light but reflect the light of their parent star.

5 Must Know Facts For Your Next Test

1. Planets can be categorized into terrestrial planets (rocky) and gas giants.
2. The discovery of planets dates back to ancient civilizations who observed them as wandering stars.
3. Kepler's laws of planetary motion describe how planets orbit the Sun.
4. The heliocentric model proposed by Copernicus placed the Sun at the center with planets orbiting it.
5. Each planet in our solar system has unique characteristics, such as size, composition, atmosphere, and satellites.

Review Questions

• What distinguishes a planet from other celestial objects like stars or asteroids?
• How did ancient astronomers categorize and understand planets?
• What is the significance of Kepler's laws in understanding planetary motion?

Related terms

Star: A massive luminous sphere of plasma held together by gravity, often at the center of a planetary system.

Asteroid:

A small rocky body that orbits the Sun, mostly found in the asteroid belt between Mars and Jupiter.

Satellite: An object that orbits a planet; can be natural like moons or artificial like human-made satellites.