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Our solar system is inside a large galaxy known as the Milky Way. All of the stars you can see at night and several hundred billion more are all bound together gravitationally into a huge cluster called a galaxy. Most of the stars in our galaxy are far enough away that they blend together in a thin band across the sky. If you are fortunate enough to view a dark sky outside of the glare of the city lights, you will see this milky band running through the constellations Cassiopeia, Perseus, Taurus, Monoceros, Vela, Crux, Norma, Sagittarius, Scutum, Aguila, Cygnus, and Lacerta. To people of long ago, this band looked like milk had been spilled along a pathway, so it was called the Milky Way. This chapter covers the radical discoveries made in the 20th century of the nature of the Milky Way and our place in it. The vocabulary terms are in boldface.
last updated: 25 May 2001