Earth in Space

Earth in Space

Section 1 Earth’s Motion and Seasons

A. Earth is a sphere because gravity acts on it.
1. Gravity is a force that attracts all objects toward each other.
2. Gravity depends on how far apart and how large the objects are.
B. Motions of Earth
1. Axis—the imaginary line drawn from the north geographic pole through Earth to the south
geographic pole
2. Rotation—the spinning of Earth on its axis; causes day and night
3. Revolution—the motion of Earth traveling around the Sun
a. Earth’s revolution causes seasons.
b. Earth’s elliptical path around the Sun is called an orbit.
4. Solstices and Equinoxes
a. Because Earth’s axis forms a 23.5 degree angle, the Sun’s position relative to Earth’s equator
constantly changes.
b. Summer and winter solstices—the longest and shortest days of the year; when the Sun
reaches its greatest distance north or south of the equator
c. Equinox—when the Sun is directly over the equator