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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.
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.
Page 862
Variable Stars: • 1920s 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.
Page 862
Variable Stars: • Stars that pulsate in brightness
because of the expansion and contraction of their outer layers.
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
Page 863 Different Types of Variable Stars:• Longer period of pulsation = greater 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.
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.
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.
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.