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Contributor: Renae Green. Lesson ID: 12984
Have you ever gazed at the night sky and wondered what was out there? Explore this lesson on stars and galaxies to learn more about our awesome universe and what those tiny points of light really are!
You have a good idea how big a golf ball, basketball, and beach ball are. You have seen them and maybe even played with them before.
It would be harder to know exactly how big the state of Texas is, or the United States of America, or the North American continent. That is because those things are too big too hold or see completely.
There are things that are even bigger than the entire world!
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.
Within the universe are different galaxies.
A galaxy is a big group of stars, gas, and related matter that stick together because they pull on each other with a strong force called gravity. A galaxy is like a huge city of stars or like a gigantic island floating in space. Each galaxy is separated from the next by millions of light-years.
The earth is in a galaxy called the Milky Way. It got its name because we see a disc-shaped, creamy band of light and stars when we look up at the night sky.
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 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, 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.
Astronomers now believe there are more than 170 billion galaxies in the world that we can see, and each contains billions of stars. Some of them contain hundreds of billions of stars!
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. Looking up at the night sky, we see billions of stars burning in space.
Before moving on, take a moment to learn some basic astronomy vocabulary. That way, you can study astronomy like an expert!
Move to the Got It? section to learn how big our galaxy is!
Note: It is important to remember that scientific theories about things like the universe are not the same as facts. To explore further, check out our lesson under Additional Resources in the right-hand sidebar.
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