Planets, asteroids, and comets all orbit the Sun. The Sun is a star that produces energy through nuclear fusion. It takes Earth 365 days to complete its orbit around the Sun, and 24 hours to complete a rotation on its axis. The average distance from Earth to the Sun is about 150 million kilometers, known as one astronomical unit.

1. Name _____________________________________________ Date ___________________ Class________________
The Structure of the Solar System
Directions: On each line, write the term from the word bank that correctly replaces the underlined words in each
sentence, Use each term only once. NOTE: You may need to change a term to its plural form.
asteroid
astronomical unit
comet
period of revolution
period of rotation
star
orbit
_____________________ 1. Many objects, including planets, travel around the Sun.
_____________________ 2. Orbiting objects made of gas, dust, and ice come from the outer parts
of the solar system.
_____________________ 3. The Sun is a(n) structure in space made of gases in which nuclear
fusion reactions occur.
_____________________ 4. In 365 days, Earth completes a(n) full journey around the Sun.
_____________________ 5. In 24 hours Earth completes a(n) full turn, also called a complete spin.
_____________________ 6. Millions of small, rocky objects orbit the Sun between the orbits of
Mars and Jupiter.
_____________________ 7. A(n) distance equal of about 150 million km is the average distance
from Earth to the Sun.