Lesson Plan - Get It!
- Have you ever wondered how big the universe is?
- How big is a galaxy?
- How about "just" a star?
The study of the stars, galaxies, and the universe is called astronomy. Learn more about the work of astronomers to answer these questions.
The word "universe" means everything.
When astronomers use the word "universe," they usually mean everything we can see.
According to the Smithsonian, “a galaxy is an assembly of stars and related matter and gas, all held together by mutual gravity. We might think of a galaxy as a super megalopolis of stars. A more common analogy is that a galaxy is a vast island in space, separated from the others by millions of light-years.”1
We live in a galaxy called the Milky Way. It got its name because when we look up at the night sky, we see a disc-shaped, creamy band of light and stars. We are contained within this band. It’s our neighborhood in the universe. People once thought the Milky Way was just a bright part of the sky, but when Galileo looked through his telescope in 1610, he realized it’s actually made up of a bunch of stars.
Until recently, people thought the Milky Way was the only galaxy. But in 1917, an observatory in Pasadena, California erected a hundred-inch-wide telescope. This was the largest telescope in the world! An astronomer named Edwin Hubble went to Pasadena to study the Andromeda nebula, or a fuzzy patch of gas and dust with this giant telescope. He discovered that the fuzz was farther away than anyone imagined. It wasn’t a nebula, after all . . . it was a whole other galaxy! This was renamed as the Andromeda galaxy. It was another island in our universe, millions of light years from the Milky Way.
This changed everything. If there was another galaxy out there that we could see, how many galaxies were out there that we couldn’t see? Astronomers now believe there are more than 170 billion galaxies in the world that we can see, and each one contains billions of stars. Some of them contain hundreds of billions of stars!
So if a galaxy is like an island in space made up of billions of stars, what is a star? A star is a great, big ball of fire in the sky.
The sun is our closest star. Think about that. There are billions of sun-like balls of fire out there in the universe. When we look up at the night sky, that is what we see; billions of stars, burning in space.
Does that make you feel small?
Before we move on, take a moment to learn some basic astronomy vocabulary. That way you can study astronomy like an expert!
Let’s move on to the Got It? section to learn just how big our galaxy is.
1 Binns, Stephen. "Cosmic Questions." Smithsonian in Your Classroom, Spring 2010, p. 02.