David learns that the sun is so large a million Earths could fit inside it.
Segment length: 7:39
- How big is the sun, and how far away is it from Earth?
- What is the sun made of, why is it hot, and will it ever burn up?
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
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
- 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
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
- Asimov, I. (1987) How did we find out about sunshine? New York: Walker &
- 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
- Pecker, J.C. (1992) The future of the sun. New York: McGraw-Hill.
- Rathbun, E. (1989) Exploring your solar system. Washington, DC: National
- The sun. (1990) Alexandria, VA: Time-Life Books.
- Taylor, P. (1991) Observing the sun. Cambridge & New York: Cambridge
- 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
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.
- heavy butcher paper or 4 large sheets of poster board
- 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
- Make a paper circle to represent the sun. It should be 2.3 meters (7.5')
- 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.
- You'll need at least two people to stand next to one marker, holding the
- The third person holds the marble, representing Earth, and walks from the
sun over to the other marker.
- How could you represent the differences in the distances between Earth
and the sun at various times of the year?
- 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.
- 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