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.