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Explorations An Introduction to Astronomy, 3/e
Thomas T. Arny

Galaxies


Galaxies479
16.1Discovering Galaxies480
Early Observations of Galaxies480
Types of Galaxies481
Differences in the Stellar and Gas Content of Galaxies485
The Cause of Galaxy Types487
Galaxy Collisions and Mergers488
16.2Measuring Properties of Galaxies490
Galaxy Distances490
Extending Our Reach: Measuring the Distance of a Galaxy Using Cepheid Variables491
The Redshift and the Hubble Law492
Measuring the Diameter of a Galaxy493
Extending Our Reach: Other Ways to Measure a Galaxy's Distance494
Measuring the Mass of a Galaxy494
16.3Dark Matter495
16.4Active Galaxies496
Radio Galaxies496
Seyfert Galaxies498
Quasars498
Cause of Activity in Galaxies499
Extending Our Reach: Measuring the Diameter of Astronomical Objects by Using Their Light Variability500
16.5Quasars As Probes of Intergalactic Space502
Gravitational Lenses503
Extending Our Reach: Dark Matter and Gravitational Lenses504
16.6Galaxy Clusters504
The Local Group505
Rich and Poor Galaxy Clusters506
Superclusters507
Project511