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You step outside on a crisp, clear night and gaze up at a sky full of sparkling stars. You wonder which one to wish upon--they're all beautiful, but so far away. Why not try wishing upon the star that's closest to our own planet Earth, the one we see almost every day, the one that provides the light and heat we need to survive? Our sun is just one of the 100 billion or so stars in our galaxy , and there are billions of other galaxies in the universe. It may seem like the sun is close to us, but it's about 150 million kilometers (93 million miles) away. It's bigger than anything we can imagine--about 1.4 million kilometers (870,000 miles) in diameter. A million Earths could fit inside it! The sun may be only one among billions of other stars in the universe, but it's the one that makes our life on Earth possible. How? By providing energy in many forms--solar power, fossil fuels, wave power , wind power. Without heat and light from the sun, Earth would be just another dark, cold place in space where life as we know it couldn't exist. Where does the sun get all this energy? The sun's mass is approximately 300,000 times more than Earth's, and the greater an object's mass, the greater the pressure at its center. Charles's law tells us that when you squeeze--or compress--a gas, it gets hot. Most of the sun's mass is composed of hydrogen gas atoms, and about 100 years ago, physicists came up with the hypothesis that the sun's tremendous mass squeezed the hydrogen atoms until they ignited, releasing heat and light energy that eventually made it through space to us. Based on calculations of the mass of the sun, they figured that the sun would burn itself out in 6,000 years. Evolutionary biologists and geologists knew from their own studies that life on Earth had been around much longer than 6,000 years, so the research continued. Decades later, a new hypothesis arose. Think about the hottest oven you can imagine, then turn up the temperature to about 25,000,000*F. That's how hot it gets in the center of the sun. At that temperature the hydrogen nuclei are moving so fast that when they crash into each other they stick together to form helium nuclei. The "fallout" from this crash is a tremendous amount of energy, released mainly in the form of heat and light. This reaction at the nuclear level is called nuclear fusion . Scientists calculate that there is enough hydrogen in the sun to continue the fusion reaction and provide heat and energy for at least another five or six billion years.
  • What is the range of temperatures on Earth? Compare this with temperatures on other planets in our solar system. Do any other planets have a similar range that would allow for human survival?
  • What kinds of energy resources do we have on Earth? How are they related to the sun? Are any of our energy resources in danger of being used up? How can we conserve our energy resources?


Just how much bigger is the sun than Earth? And how far away is it? If you can't get a reservation on the next space shuttle flight, you'll have to go out to a field with a few friends and a few supplies to find the answers. You'll be amazed at what you observe when you compare the size of Earth with that of the sun and see how far you'd have to travel to get from one to the other.


  • heavy butcher paper or 4 large sheets of poster board
  • scissors
  • tape or glue
  • meter stick
  • long-distance measuring tape
  • marble, about 2 cm (3/4") in diameter, to represent Earth
  • athletic field or large open area, at least 250 meters (820') long
  • stones or bricks to use as markers
  • at least three people
  1. Make a paper circle to represent the sun. It should be 2.3 meters (7.5') in diameter.
  2. Next, go outside and measure a length of 246 meters (807') on an athletic field or other large area. Use bricks or stones to mark each end.
  3. You'll need at least two people to stand next to one marker, holding the paper sun.
  4. The third person holds the marble, representing Earth, and walks from the sun over to the other marker.


    1. How could you represent the differences in the distances between Earth and the sun at various times of the year?
    2. How far from the sun are other planets in our solar system? On a large sheet of paper position each planet at its appropriate distance from the sun and represent its size to scale.
    3. Discuss the difficulties involved in representing relative diameter and distance in the same model.


  • Darling, D. (1984) The sun: Our neighborhood star. Minneapolis: Dillon
  • Discover space. (1993) Novato, CA: Broderbund (MS-DOS).
  • Fowler, A. (1991) The sun is always shining somewhere. Chicago: The
    Children's Press.
  • Pecker, J.C. (1992) The future of the sun. New York: McGraw-Hill.
  • Rathbun, E. (1989) Exploring your solar system. Washington, DC: National
    Geographic Society.
  • The sun. (1990) Alexandria, VA: Time-Life Books.
  • Taylor, P. (1991) Observing the sun. Cambridge & New York: Cambridge
    University Press.
  • Where in space is Carmen Sandiego? (1993) Novato, CA: Broderbund
    (Macintosh, MS-DOS, Windows).
  • The view from Earth. (1992) Burbank, CA: Warner New Media (CD-ROM for

Additional sources of information

Teacher Resource Center
Jet Propulsion Laboratory
M.S. C-S 530
4800 Oak Grove Drive
Pasadena, CA 91109

Community resources

Observatory or planetarium
Local amateur astronomical society