The Eight Planets
- Our solar system includes the sun, the planets, and many smaller objects.
Astronomical Unit – the average distance between the Earth and the sun; approximately 150
million kilometers (symbol, AU)
Inner Planets – The inner planets are known as the terrestrial planets because their surfaces are
dense and rocky. (Mercury, Venus, Earth, Mars)
Outer Planets – The outer planets are gas giants, which are large and mostly made of gas.
(Jupiter, Saturn, Uranus, Neptune)
Section Review
2. When was the planet Uranus discovered?
b. in the 18th century
3. The invention of what instrument helped early scientists discover more bodies in the solar
system?
The telescope
4. Which of the eight planets are included in the outer solar system?
Jupiter, Saturn, Uranus, Neptune
5. Describe how the inner planets are different from the outer planets.
The inner planets are dense and rocky. The outer planets are extremely large and made
mostly of gas.
6. If Venus is 6.0 light-minutes from the sun, what is Venus’s distance from the sun in
astronomical units?
1 AU = 8.3 light-minutes
x AU = 6 light-minutes
x = 6/8.3
x = .7 light-minutes