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Celestial Formations. 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
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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
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
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
Irregular Galaxies • Have no definite shape • Large and Small Magellanic Clouds are some examples
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
Globular Cluster • Group of stars in spherical shape • Many contain more than 100,000 stars • Example is the cluster in the constellation Hercules
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