Name: ___________________________ Date: __________________

Each sentence needs one or more semicolons or commas. Insert the appropriate marks for each sentence below.

1. The oldest science is the study of the stars and planets; even ancient peoples looked up at the night sky with wonder and awe.
   
   
2. Early scientists plotted the positions and changing brightness of the stars, and people worshipped the sun and the moon as gods.
   
   
3. Modern scientific discoveries have led to new knowledge about our solar system, but astronomers continue to gather more information every day.
   
   
4. We've learned that our sun is a star; it radiates heat and light because of nuclear reactions inside its core.
   
   
5. The mass of the universe, including our bodies, is made up of elements from stars that exploded billions of years ago; therefore, humans are the stuff of stars.
   
   
6. A galaxy is a huge collection of stars bound together by gravity; our sun and its satellites are part of the spiral-shaped Milky Way galaxy.
   
   
7. The universe is unbelievably vast; astronomers estimate that there are at least one billion different galaxies close enough to photograph.
   
   
8. Our own solar system is so big that it could take up to 12 years to journey from Earth to the outermost planet, yet it occupies only a tiny area of this vast universe.
   
   
9. There are two types of planets; Earth and the three planets like it (Mercury, Venus, and Mars) are known as the terrestrial planets.
   
   
10. The other group consists of the planets that resemble Jupiter; these Jovian planets include Jupiter, Saturn, Uranus, and Neptune.
    
    
11. Pluto does not resemble either Earth or Jupiter, so some astronomers suggest that it be classified as an asteroid rather than a planet.
    
    
12. The farthest planet from the sun is Pluto; it orbits the sun only once every 248 years.
    
    
13. Pluto is the only planet that has not been visited by a probe from Earth, but scientists hope to launch one in the near future.
    
    
14. Venus is the closest planet to the Earth; as a result, it is the brightest object in our nighttime sky.
    
    
15. Jupiter is the largest planet of our solar system; also, it has sixteen moons more than any other planet.
    
    
16. One of Jupiter's moons, Europa, may have an ocean of liquid water; if it does, it could contain life.
    
    
17. Saturn is distinctive because of its rings; they are believed to be composed of ice and rocks.
    
    
18. Many scientists believe that Mars may have once supported life, for a Martian asteroid contains what looks like fossils of tiny organisms.
    
    
19. Neptune and Uranus are twins; both have rings like Saturn and a similar composition.
    
    
20. Mercury is closest to the sun; thus, its average surface temperature is 350 degrees during the day.