G8 – Solar Systems, Galaxies and the Universe Approaching -02

Introduction

You gaze into the night sky and ponder what’s beyond the stars you can see. It is difficult to imagine the scale of the universe from this vantage point. We can see more stars than we can count on a typical night. Even so, what we are seeing is only a tiny fraction of what is up there.

In fact, as we look at the many stars in the sky, we are seeing only the stars in our own star neighborhood. It is called the Milky Way Galaxy. Our galaxy has billions of stars, solar systems, planets, and other celestial objects. Our solar system is located inside our galaxy.

Planets versus Stars

For millennia, people have gazed to the sky, hoping to understand it. The ancient Greeks noticed that a few objects in the night sky moved differently than others. They referred to them as wanderers. We now know these wanderers as planets. They named these wandering points of light after their gods and goddesses.

You know them as Mercury, Venus, Mars, Jupiter, and Saturn. Today we know that we have eight planets in our solar system. Also orbiting our Sun are five dwarf planets and over 165 moons. There are also many, many asteroids and other small objects in our solar system. They all revolve around the Sun, our closest star.

Our solar system spans over 6 billion miles. That is like traveling 240,000 times around Earth. In fact, scientists use a unit of measure called the astronomical unit (AU). An AU is much easier to work with as opposed to the large numbers. One astronomical unit is equal to the distance between the Sun and Earth. Therefore, 1 AU equals about 150 million km (93 million miles).