Astronomy 63 - The Solar System - The Basics

Overview

This lecture introduces the solar system, its main components, and focuses on the Sun's size and composition compared to everything else in the system.

Defining the Solar System

• A solar system is a star and anything gravitationally bound and orbiting that star.
• The definition includes planets, moons, asteroids, comets, and all objects that orbit the star.
• Objects just passing through and not bound by gravity are not considered part of the solar system.
• Our solar system is simply called "the Solar System," and it is part of the Milky Way galaxy.
• The Milky Way is the galaxy, not the name of our solar system.

The Sun: Center of the Solar System

• The Sun is by far the largest object in the Solar System.
• No planet or other object comes close to the Sun's size.
• You could fit over 100 Earths across the Sun's diameter and over a million Earths inside its volume.
• All other objects combined (planets, asteroids, etc.) make up less than 1% of the solar system's total mass; the Sun is nearly 99%.

Composition of the Sun

• The Sun is a massive ball of hot gas, not a solid or liquid.
• The most common elements in the Sun are hydrogen (about 75%) and helium (about 25%).
• These elements are also the most abundant in the universe.
• The Sun's composition reflects the overall makeup of the universe.

Key Terms & Definitions

• Solar System — A star and everything gravitationally bound to it.
• Milky Way — The galaxy containing our Solar System.
• Sun — The star at the center of our Solar System, composed mostly of hydrogen and helium.
• Hydrogen — The most abundant element in the universe and in the Sun.
• Helium — The second most abundant element in the Sun and the universe.

Action Items / Next Steps

• Begin reading Chapter 6 in the textbook to continue learning about the solar system.