KEY CONCEPT
Earth rotates on a tilted
axis and orbits the Sun.
STANDARDS
8–4.4 Explain the
motions of Earth and
the Moon and the
effects of these motions
as they orbit the Sun
(including day, year,
phases of the Moon,
eclipses, and tides).
8–4.5 Explain how the
tilt of Earth’s axis
affects the length of
the day and the amount
of heating on Earth’s
surface, thus causing
the seasons of the year.
VOCABULARY
axis of rotation p. 620
revolution p. 621
season p. 622
equinox p. 622
solstice p. 622
BEFORE, you learned
NOW, you will learn
• Stars seem to rise, cross the sky,
and set because Earth turns
• The Sun is very large and far
from Earth
• Earth orbits the Sun
• Why Earth has day and night
• How the changing angles of
sunlight produce seasons
EXPLORE Time Zones
What time is it in Iceland right now?
PROCEDURE
1
MATERIAL
Find your location and Iceland on the map.
Identify the time zone of each.
time zone map
2 Count the number of hours between your
location and Iceland. Add or subtract that
number of hours from the time on your clock.
WHAT DO YOU THINK?
• By how much is Iceland’s time earlier or later
than yours?
• Why are clocks set to different times?
Earth’s rotation causes day and night.
When astronauts explored the Moon, they felt the Moon’s gravity
pulling them down. Their usual “down”—Earth—was up in the
Moon’s sky.
As you read this book, it is easy to tell which way is down. But is
down in the same direction for a person on the other side of Earth?
If you both pointed down, you would be pointing toward each other.
Earth’s gravity pulls objects toward the center of Earth. No matter where
you stand on Earth, the direction of down will be toward Earth’s center.
There is no bottom or top. Up is out toward space, and down is toward
the center of the planet.
As Earth turns, so do you. You keep the same position with respect
to what is below your feet, but the view above your head changes.
In what direction does gravity pull objects near Earth?
Chapter 18: Earth, Moon, and Sun 619