Arny/Astronomy

Explorations an Introduction to Astronomy Thomas T. Arny

Instructor Resources

CHAPTER 16 - GALAXIES

16-1 Discovering Galaxies

Early Observations of Galaxies
Types of Galaxies
Differences in the Stellar and Gas Content of Galaxies
The Cause of Galaxy Types
Galaxy Collisions and Mergers

16-2 Measuring Properties of Galaxies

Galaxy Distances
The Redshift and the Hubble Law
Extending Our Reach - Other Ways to Measure a Galaxy's Distance
Measuring the Diameter of a Galaxy
Measuring the Mass of a Galaxy

16-3 Dark Matter

16-4 Active Galaxies

Radio Galaxies
Seyfert Galaxies
Quasars
Extending our Reach - Measuring an Object's Diameter from its Light Variation
Cause of Activity in Galaxies

16-5 Quasars as Probes of Intergalactic Space

Gravitational Lenses

16-6 Galaxy Clusters

The Local Group
Rich and Poor Galaxy Clusters
Superclusters

Goals

Types of other galaxies and their differences and basic features (E, S, and Irr). Theories of how these types form. Properties of active galaxies (Seyfert, Radio, and Quasars). Model for active galaxies. Use of Hubble Law. Dark Matter problem. Properties of galaxy clusters and superclusters.

Dark matter problem might be emphasized to illustrate that we do not know all the answers. Can also serve as example of hypothesis testing and scientific method.

Section 16-5 can be omitted with no loss of continuity. In fact, the only material really important for understanding Chapter 16 is the Hubble Law. This chapter can serve as a reminder that not all astronomical questions have answers!

Clarify that galaxies consist of numerous stars and are held together by gravity. The factors that determine what type a galaxy becomes are uncertain, but probably include amount of initial rotation and random motions.

In discussing the Hubble Law, point out that the recession of galaxies is not a standard Doppler shift but arises from the expansion of the Universe. A reference that some students might find helpful on this point is Odenwald, Sten and Richard Tresch Fienberg. "Galaxy Redshifts Reconsidered." Sky and Telescope. 85 (February, 1993): 31.

Key Terms

Galaxy
Spiral Galaxy
Elliptical Galaxy
Irregular Galaxy
Barred Spiral Galaxy
Galactic Cannibalism
Recession Velocity
Hubble Law

Hubble Constant
Megaparsec
Dark Matter
Active Galaxy
Radio Galaxies
Jets
Seyfert Galaxies
Quasar

Gravitational Lens
Galaxy Cluster
Local Group
Rich Cluster
Poor Cluster
Supercluster

Animations

Chapter 16 An explanation of superluminal motion

Chapter 16 The pancake model of the formation of clusters of galaxies

16.12 Galaxies with tails

Additional Readings

Cowen, Ron. "The Debut of Galaxies." Astronomy 22 (December 1994): 44.
Croswell, Ken. "A Milestone in Fornax." Astronomy 23 (October 1995): 34.
Djorgovski, S. George. "Fires at Cosmic Dawn." Astronomy 23 (September 1995):36.
Falbo-Kenkel, Maria and Joe Lohre. "Simple Gravitational Lens Demonstrations." The Physics Teacher 34 (December 1996): 555.
Gallagher, Jay and Jean Keppel. "Seven Mysteries of Galaxies." Astronomy 22 (March1994): 38.
Price, Jill S. and KarenAnn Caldwell. "Galaxies that go Bump in the Night." Mercury 24 (July/August 1995): 23. (This article contains a very nice photographic version of the Hubble Tuning-fork diagram).
Sciama, D.W. Modern Cosmology and the Dark Matter Problem. Cambridge; New York: Cambridge University Press, 1993.
Trimble, Virginia and George Musser. "Clusters, Lensing, and the Future of the Universe." Mercury 24 (May/June 1995): 6.

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