CELESTIAL FORMATION

Galaxy A large collection of stars Galaxies contain star groups Galaxies only contain 1% of matter

in the universe The remaining 99% of matter in the

universe is “empty” space consisting of gases and dust

Milky Way Galaxy

The galaxy where we are located Contains 100 to 200 billion stars Also contains gas and dust clouds

(nebulae) Approximately 100,000 light years in

diameter and about 15,000 light years thick

Solar system is located in the outer spiral arm of the Milky Way, about 30, 000 light years from the center of the galaxy

Milky Way Galaxy

Rotates about its center It takes 200 million years for the

solar system to revolve around the galaxy

The Milky Way Gaalaxy

Types of Galaxy

Elliptical Galaxies

Vary in shape from nearly spherical to resembling a flat disk

Contain very little dust Have stars that are generally older

than those in other types

Elliptical Galaxy

Spiral Galaxies

Made up of thick mass of material and flattened arms that spiral around the center

Milky Way and Andromeda galaxy are spiral galaxies

Spiral Galaxy (Andromeda)

Irregular Galaxies

Have no definite shape Large and Small Magellanic Clouds

are some examples

Irregular Galaxy

Star Clusters

Smaller groups of stars within a galaxy

They are gravitationally bound There are two types of star clusters

in the Milky Way galaxy Most star clusters are far from the

solar system and appear as fuzzy patches in the night sky

The open cluster and the globular cluster

Open Cluster

Contains large, loosely organized groups of stars

Pleiades, one of its examples, can be seen in the constellation of Taurus in winter

Open Cluster (Pleiades)

Globular Cluster

Group of stars in spherical shape Many contain more than 100,000

stars Example is the cluster in the

constellation Hercules

Globular Cluster

Multiple Star System

Clusters that contain stars in much smaller groups

Binary stars are stars found in pairs Eclipsing binary is a binary star

system in which one star blocks out the light from its companion star

Binary Stars