Notes-Galaxies The Universe includes everything that we know exists, everything we can see or know about in space is included.

Galaxies: Most of the visible universe is made up of galaxies. A Galaxy-is a group of stars, dust, and gases held together by gravity. There are billions of galaxies in the universe and each one contains billions of stars.

Formation of Galaxies Formed from HUGE clouds of gas. Gas particles drawn closer to each other by their gravity. As the gas pulled together, they began to move around each other.

Formation of Galaxies Leads to most galaxies, but not all, being spun to a flat, disc shape.

Classification of Galaxies Classified by shape, brightness, and position in sky.

Classification: Elliptical Elliptical Galaxies- Contain mostly older stars Stars crowded to the center Range in shape from round to oval

Elliptical Galaxy

Classification:Spiral Spiral Galaxies- Disk shaped Mix of young and old stars Spiral arms around large dense center

Classification: Irregular Irregular Galaxies- Very irregular in shape No dense center Composed mostly of young stars

We live in the Milk Way Galaxy! The name Milky Way came from the dim “milky” band seen across the night sky Is an average Spiral Galaxy Contains over 200 billion stars 100, 000 Light Years across

Milky Way Galaxy It is difficult to tell exactly what our galaxy looks like because we are in it. Scientists think it is a disk shaped spiral bound galaxy with a large spherical center. Scientist believe we are on the outer edge of one of it’s arms

Hubble Images of Milky Way

Dark Matter There is also a lot in the sky we can’t see We know it’s there because other things move around it It has a gravitational pull But scientists have no idea what it is…so they call it Dark Matter