Chapter 30 1 Galaxies and The Universe Objectives

Chapter 30. 1 Galaxies and The Universe

Objectives �Students will be able to determine the size and shape of our galaxy. �Students will be able to distinguish the different kinds of variable stars. �Students will be able to identify different kinds of stars in a galaxy and their location.

Word of the Day �Galaxy: Any of the very large groups of stars and associated matter found throughout the universe.

Galaxies and The Universe Main Idea, Page 862 Stars with varying light output allowed astronomers to map the Milky Way which has a halo, spiral arms, and a massive blackhole at its center.

Galaxies and The Universe Page 862 Milky Way Galaxy: Disk shape collection of stars where we are located.

Galaxies and The Universe Page 862 Variable Stars: • 1920 s astronomers try to map the locations of globular clusters of stars. • To do so, they estimated the distances to the clusters by identifying variable stars in them.

Galaxies and The Universe Page 862 Variable Stars: • Stars that pulsate in brightness because of the expansion and contraction of their outer layers.

Galaxies and The Universe Page 863 Different Types of Variable Stars: 1. RR Lyrae variables: Pulse from 1. 5 hours to ever 1 day. 2. Cepheid variables: Pulse from 1 day to 100 days

Different Types of. Universe Variable Stars: Galaxies and The • Longer period of pulsation = greater Page 863 • luminosity. Luminosity is then compared to star’s magnitude (brightness. ) Allows astronomers to calculate how far away a star must be to appear so bright.

Galaxies and The Universe Page 863 The Galactic Center: A region of high star density. • • RR Lyrae variables used to determine distance to globular clusters of stars orbiting the center of the Milky Way. Clusters’ distribution was centered on a point 28, 000 light years away.

Galaxies and The Universe Page 863 The Shape of the Milky Way: • Determined by mapping with radio waves. Radio waves penetrate gas and dust without being disturbed. • • Map showed that galactic center is surrounded by a nuclear bulge. Around the bulge is a disk shaped halo.

Galaxies and The Universe Page 864 Spiral Arms: • • Along with the disk shape and bulge, the Milky Way has 4 Major Spiral Arms and numerous minor arms. Arms were discovered using hydrogen emissions spectra.

Galaxies and The Universe Page 864 Spiral Arms: • • Some galaxies are shaped like a bar and not a disk. The shape of a galaxy is determined by the density of gas in its halo. Bulge: Made of older red stars. Bar: Made of young stars and discs that form from hydrogen gas.