6: Measuring Cosmic Distances

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Kim Coble, Kevin McLin, & Lynn Cominsky
San Francisco State University, Chico State University, & Sonoma State University

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Chapter 6 explores the various ways in which humanity has learned to measure the distances to the stars and beyond. Examples of several geometrical methods, the standard rulers, and standard candles are presented. The chapter concludes with a summary of the Cosmic Distance Ladder, which puts together of all the measuring techniques to bridge our understanding of distance in the Universe.

6.0: Measuring Cosmic Distances Introduction
Without a knowledge of cosmic distance, we cannot understand how much energy a faraway object is emitting. In physics (including astrophysics), knowing the energy produced by a system is fundamental to developing models that describe the nature of that system. In this chapter, you will learn how scientists measure the distances to and between objects in the Universe.
6.1: Geometrical Methods
You will know that the ancient Greeks measure the size of Earth and the Moon as well as the distance between them using geometry. You will know the principle of parallax and when it applies. You will be able to give examples from everyday life and from astronomy
6.2: Standard Ruler
6.3: Standard Candle
6.4: The Cosmic Distance Ladder
In this chapter, we have explored various techniques astronomers use to calculate distances in space. Different techniques work well for different distances, but the techniques for objects farther away typically rest on calibrations from studies of similar objects that are closer. As we go farther out into the Universe, distance measurements typically become both more difficult and uncertain. To be confident of our results, it is important that we use multiple independent techniques.
6.5: Wrapping It Up 6 - The Supernova of 1885
6.6: Mission Report 6 - Distance Measurement

Thumbnail: This beautiful image shows a giant cluster of stars called Messier 80, located about 28,000 light-years from Earth. Such crowded groups, which astronomers call globular clusters, contain hundreds of thousands of stars, including some of the RR Lyrae variables discussed in this chapter. Especially obvious in this picture are the bright red giants, which are stars similar to the Sun in mass that are nearing the ends of their lives. (credit: modification of work by The Hubble Heritage Team (AURA/ STScI/ NASA)).