show #1206

David learns that the sun is so large a million Earths could fit inside it. Segment length: 7:39


Insights & Connections



Main activity

Try this


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.


Charles's law When you squeeze a gas, it heats up.

evolutionary biologists scientists who study the development of organisms or species from their initial form to their present state

galaxy group of stars

helium light, colorless inert gas that places second on the periodic chart. It's often used to inflate party balloons and blimps.

hydrogen the lightest of all known substances, it comes in first on the periodic chart

mass measurement of how much matter there is (not how much that matter weighs)

nuclear fusion fusing, or joining, the smallest of nuclei to release tremendous amounts of energy

nuclear reaction reaction that takes place at the core of an atom. It converts mass into energy.

wave power energy generated by waves in the sea or in rivers and lakes


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


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.


  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.


When we talk about the sun, we must use extremely large numbers. When working with very large or very small numbers, we use scientific notation, which means rewriting a number as the product of a number between 1 and 10 and a power of 10. For example, the sun's diameter, approximately 1,391,000 km, would be written as 1.391 x 106 km. Write some other large numbers in scientific notation.


Simulate the transfer of energy that takes place in a nuclear reaction and recycle sheets of paper at the same time! Get a group of at least six people to form a circle, each wearing safety glasses. Give each person two sheets of used paper (everyone should have the same size and weight of paper) and ask them to crumple the sheets to make two paper balls. Each person in the circle should hold a paper ball in each hand, and be ready to toss them in the air. The leader tosses (don't throw) a ball at one person. Whoever is hit by the ball quickly tosses the two balls she or he is holding at the group. The two people that person hits in turn toss their papers balls at the group. This continues until everyone has tossed their paper balls. The process should only take a few seconds. Observe how the tossing action speeds up as more people get involved!


Sunlight looks colorless until it is refracted (bent) by water molecules in the air (raindrops), and displayed in the sky as a rainbow. There are many ways to capture white sunlight and create your own rainbow. Cut a slit that is 1 cm (3/8") wide and 20 cm (8") long out of the middle of a sheet of opaque white paper or cardboard. Tape this sheet to the side of a clear glass of water so the sheet is standing vertically next to the glass. Place an 8 1/2" x 11" sheet of white paper on a table next to a sunlit window. Position the glass of water and the slit paper on top of the other sheet so that the paper with the slit is between the glass and the window. The room must be darkened except for a small beam of sunlight. As sunlight passes through the slit, it will be refracted by the water, creating a spectrum of colors that you'll see on the plain sheet of paper.
Newton's Apple is a production of KTCA Twin Cities Public Television. Made possible by a grant from 3M. Educational materials developed with the National Science Teachers Association.