The Structure of Our Galaxy

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: The Nucleus of a Galaxy

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:03 The Milky Way Galaxy
  • 2:04 The Disk Component
  • 3:53 The Halo, Central…
  • 5:17 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed
Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

If you ever looked up at the night sky far away from city lights, you would've seen a band of light across the night sky and lots of stars scattered around the rest of the sky. Why? The structure of our galaxy will explain exactly why.

The Milky Way Galaxy

You live at home. Your home lives in a city. The city lives in a state, which lives in a country, which lives on Earth. The Earth lives in our solar system, which calls our galaxy, the Milky Way Galaxy, home.

You know the structure of your home. Maybe it's made of brick. Maybe it's a split-level home. You even know the outline of your city and the boundaries of your country. You can use a satellite to see our Earth from a distance. But we have no way of seeing our galaxy from far away.

So, what's the structure of something we can't see from afar, something we are immersed within? What's the structure of our galaxy? This lesson will outline the answer astronomers have found from years of research.

When you look up at the night sky, it looks like the stars are pretty evenly distributed all over the cosmos. But the reality is that stars clump together into galaxies. A galaxy is a large but isolated collection of stars, interstellar gas and dust, star clusters, and nebulae that orbit around a common center of mass. When I say they're isolated clumps, I say that because galaxies are separated by vast spaces that are mainly empty.

And so it follows that just about every single thing you see up in the night sky with the unaided eye is part of our galaxy, the Milky Way galaxy, a barred, spiral galaxy that contains our sun and Earth, one that is visible as the Milky Way. The Milky Way is a wispy band of light made by the glow of our galaxy's stars that stretches across the sky. It's best seen when it's very dark outside and no light pollution is present from nearby cities or streetlights.

The Milky Way encircles us, and we see it basically as an edge-on view of our galaxy. Meaning, we are looking at it from within the plane of our galaxy. This is the reason for why it appears as a band around the sky.

The Disk Component

To help better understand how this is so, imagine our galaxy is a wafer disk. The disk component of our galaxy is the disk of our galaxy, the components within the plane of the galaxy. But what is the plane of the galaxy?

Well, let's face it; if you're looking at the wafer face-on, it looks like a flat circle. But if you look at it edge-on, that's the plane of the galaxy, and it looks like a thin band stretching from left to right, just like it would on our own night sky.

This means that when you go outside at night and look up at the night sky, you see one of two things. If you look out at the sky in the plane of the disk, you see the Milky Way. If you look perpendicular to the plane of our galaxy, you see a much sparser collection of stars scattered throughout space.

The disk component of our galaxy contains the majority of the galaxy's stars and almost all of the interstellar gas and dust. The interstellar dust and gas is where stars are born, and thus, almost all star formation occurs in the galaxy's disk. Actually, if you look at the image on your screen, you can see the Milky Way. The dark streaks that stretch across the Milky Way occur thanks to the interstellar dust located in the plane of the Milky Way galaxy.

While most of the stars in the disk are middle-to lower-main-sequence stars, there are exceptions. There are some white dwarfs, red giants, and even very massive class O and B stars. The latter two are rare but are so luminous that they are the ones that provide a lot of light emanating from the disk itself.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account