Galaxies Chapter 15 3 pp 450 453 What

Galaxies • Chapter 15 -3 • pp 450 - 453

What are Galaxies? • Galaxies are large groupings of stars in space. • Galaxies also contain gas clouds and dust • Galaxies come in a variety of sizes and shapes.

Spiral Galaxies • Spiral galaxies have a bulge at the center and very distinctive spiral arms.

The Milky Way • From earth, we see our galaxy as a bright band of stars that cuts across the night sky. • 200 billion stars including the sun. • Our sun is located about two-thirds of the way between the center of the galaxy and its edge.

Elliptical Galaxies • Round or oval in shape • Up to 5 trillion stars • Very bright centers • Very little dust or gas • No new stars forming • Contain only old stars

Irregular Galaxies • Have no definite shape • Some form when galaxies collide

Contents of Galaxies Globular cluster – highly concentrated group of stars Nebula – cloud of gas and dust where stars are born Open cluster – group of 100 – 1000 stars that are close together relative to other stars.

Quasars • Most distant objects in our universe • Star-like sources of energy located in the centers of galaxies • May be caused by super massive black holes in the cores of galaxies • Power of 10 trillion suns

Origins of Galaxies • Because light takes time to travel through space, looking through a telescope is like looking back in time. (Sunlight that falls on the Earth is 8. 3 minutes old) • Looking at distant galaxies reveals what early galaxies looked like. • This information gives scientists ideas about how galaxies form and how galaxies change over time.