Download Planets orbit the Sun at different distances.

KEY CONCEPT
Planets orbit the Sun at
different distances.
STANDARDS
8–4.1 Summarize the
characteristics and
movements of objects
in the solar system
(including planets,
moons, asteroids,
comets, and meteors).
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
How do planets form?
PROCEDURE
1
VOCABULARY
astronomical unit (AU)
p. 657
ellipse p. 657
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.
MAIN IDEA AND DETAILS
Put sizes and distances
in the solar system into
a chart.
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 the large but
distant planets Uranus and Neptune.
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, such as those called comets and
asteroids. However, these objects are usually too far away and not
bright enough to see without a telescope.
Why do planets look bright?
Chapter 19: Our Solar System 655