Astronomy
Lesson 1 of 4 8 min +55 XP

The Solar System

The Sun, planets, and orbits.

What you'll learn

  • Order the planets
  • Explain what an orbit is
  • Distinguish rocky and gas planets
The family around the campfire

The Sun is a campfire and the planets are people sitting around it at different distances — close ones roasting, far ones shivering — each circling on its own path. The solar system is that gravity-held gathering, with everyone orbiting the fire.

Our neighborhood in space

Eight planets orbit the Sun, held by its gravity. The inner four (Mercury, Venus, Earth, Mars) are small and rocky; the outer four (Jupiter, Saturn, Uranus, Neptune) are large gas and ice giants. An orbit is the curved path one object takes around another under gravity.

Order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Lab · Rocky or gas?
  1. List the four planets closest to the Sun.
  2. List the four farthest.
  3. Label each group rocky or gas/ice giant.

What you should see: The inner four are rocky; the outer four are gas and ice giants.

Knowledge Check

+15 XP / correct

1. Which planet is closest to the Sun?

2. What holds the planets in orbit around the Sun?