Warm-up: How far is an Astronomical Unit? Go over 10 questions Sun – Earth - Moon System Notes Sun – Earth – Moon System Homework: Finish the lab.

Introducing the Sun-Earth-Moon System Notes Lesson 2

Background Info The Sun is the only star in our solar system. The other stars we see at night are part of a larger galaxy A galaxy is a collection of dust, gas, and stars. Ours is called the “Milky Way.”

Our Solar system is just a small part of the “Milky Way” galaxy. Our sun is just an “average star” and one of 100 billion or so stars in our galaxy. Joined by billions of other galaxies in the universe. The term “average star” is how astronomers classify stars by temperature, luminosity, and mass. The sun is not unusually hot or cold, old or young, or large or small.

Distances in Space Though the Sun seems close to the Earth, it is about 150 million km (93 million miles ) away or about 12,000 Earths away. The Sun’s diameter is 1,392,000 km (864,327 miles). The Earth’s diameter is 12,756 km (7,926 miles). One million Earths could fit inside of the Sun. The Moon’s diameter is 3,500 km (2,159 miles).

The Moon and the Sun look to be similar sizes because the moon is about 400 times smaller than the Sun but also about 400 times closer than the Sun. The Earth’s distance from the Sun (150 million km) is used as a standard unit for measuring distances in space. This unit is known as an Astronomical Unit or AU. Jupiter is 778,400,000 km from the Sun or 5.2 AU.

About 12,000 Earths could fit between the Earth and the Sun. About 30 Earths could fit between the Earth and the Moon. About 109 Earths would equal the diameter of the Sun.

Movement of the Earth Rotation – Indicates the spinning of an object on a central axis. Earth makes 1 rotation about every 24 hours. Revolution – Means the orbiting of on object around another. Earth makes 1 revolution about every 365 days. We will commonly use the word “Orbit” to describe a “Revolution.”

The orbit of the Earth around the Sun is an elliptical orbit. The orbit of the Moon around the Earth is nearly a circular orbit. The Moon rotates on its axis in about days. The Moon makes one orbit of the Earth in about days.