Chapter 20

The Universe

20-1

What is earth’s place in the universe?

The Universe

Astronomy is the study of space and the objects in it.

Earth is part of the Milky Way Galaxy.A galaxy is a huge grouping of stars.There are three types of galaxies; spiral,

elliptical, and irregular.

The Planets

The Sun and the bodies around it make up our solar system.

An asteroid is a small body of rock and metal that orbits the Sun.

Comets are small icy bodies that orbit the Sun.Mars is covered with red dust and has strong

winds that blow the dust. Jupiter has the strongest force of gravity.

The Planets (continued)

An astronomical unit is the average distance of Earth and Sun. AU’s are used to measure distances in space.

Venus is very different from Earth because it has thick clouds and an atmosphere of carbon dioxide.

Planets orbit the Sun because of the Sun’s force of gravity on them.

Why Planets Differ

A planet’s size affects how strong the gravity is at its surface.

The planet’s atmosphere and distance from the sun determine why planets differ.

The Sun and Inner Planets Video