s8pe-41301-ca
10/28/05
12:34 PM
MAZER
Page 413
KEY CONCEPT
Planets orbit the Sun at
different distances.
CALIFORNIA
Content Standards
8.2.g Students know
the role of gravity in
forming and maintaining the shapes of
planets, stars, and the
solar system.
8.4.d Students know
that stars are the
source of light for all
bright objects in outer
space and that the
Moon and planets
shine by reflected
sunlight, not by their
own light.
8.4.e Students know
the appearance,
general composition,
relative position and
size, and motion of
objects in the solar
system, including
planets, planetary
satellites, comets,
and asteroids.
VOCABULARY
astronomical unit (AU)
p. 415
ellipse p. 415
MAIN IDEA AND DETAILS
Put sizes and distances
in the solar system into
a chart.
BEFORE, you learned
NOW, you will learn
• Earth orbits the Sun
• The Moon is Earth’s natural
satellite
• The Moon’s features tell us
about its history
• What types of objects are in
the solar system
• About sizes and distances in
the solar system
• How the solar system formed
EXPLORE Planet Formation (8.4.e)
How do planets form?
PROCEDURE
1
Fill the bowl about halfway with water.
2 Stir the water quickly, using a circular
motion, and then remove the spoon.
MATERIALS
•
•
•
•
bowl
water
spoon
wax pieces
3 Sprinkle wax pieces onto the swirling water.
WHAT DO YOU THINK?
• In what direction did the wax move?
• What else happened to the wax?
Planets have different sizes and distances.
You may have seen some planets in the sky without realizing it. They
are so far from Earth that they appear as tiny dots of light in the darkened sky. If you have seen something that looks like a very bright star
in the western sky in the early evening, you have probably seen the
planet Venus. Even if you live in a city, you may have seen Mars,
Jupiter, or Saturn but thought that you were seeing a star. Mercury
is much more difficult to see. You need a telescope to see three of the
planets in our solar system—Uranus, Neptune, and Pluto.
Like the Moon, planets can be seen because they reflect sunlight.
Planets do not give off visible light of their own. Sunlight is also reflected
by moons and other objects in space, called comets and asteroids.
However, these objects are usually too far away and not bright enough
to see without a telescope.
check your reading
Why do planets look bright?
Chapter 13: Our Solar System 413
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