Chapter 24

Earth, Moon, and Sun

24.1 Planet Earth

Lesson Objectives

• Recognize that Earth is a sphere, and describe the evidence for this conclusion.


• Describe what gravity is, and how it affects Earth in the solar system.


• Explain what causes Earth’s magnetism, and the effects that magnetism has on the
  Earth.

Introduction

The Earth and Moon revolve around each other as they orbit the Sun. As planet Earth
rotates and revolves, we experience cycles of day and night as well as seasons. Earth has a
very large moon for an inner planet. We are the only inner planet that does, so how did
the Moon form and what is the surface of the Moon like? We revolve around an average,
ordinary star, the Sun. It does not look like any of the other stars we see in the sky. What
can we discover about our amazing Sun?

Earth’s Shape, Size, and Mass

Every day you walk across some part of Earth’s surface, whether that surface is your yard
or the sidewalks by your school. For most of us, a walk outside means walking on fairly flat
ground. We don’t usually stop and realize that the Earth is asphere, an object similar in
shape to a ball. How do we know that Earth is a sphere? How could you convince someone
that even though the surfaces we walk on look flat, the Earth as a whole is round?