How Does Galaxies, part 1: Crash Course Astronomy #38 Work?

Galaxies are like giant cities in space made of stars, and we're going to see how they form, kind of like how neighborhoods grow when more people move in.

Imagine you have a big, empty playground. One day, a bunch of kids (like stars) show up and start running around. At first, they’re all scattered, but as more kids come, they group together, some form little clusters, others make bigger groups. That’s kind of like how galaxies are born: from clouds of gas and dust in space (gas clouds), which slowly pull each other closer until they become stars.

Now imagine those neighborhoods: the kids (stars) keep moving around, but some have a rule, everyone has to stay close. That’s like gravity, the invisible force that keeps stars together in galaxies. Just as you might be pulled back to your favorite spot on the playground, stars are kept from flying off into space by gravity.

So when we look up at the night sky and see lots of stars grouped together, we’re really seeing a galaxy, a big, busy city in the universe!