Chapter 09

Chapter 09 - Note that the following lectures include...

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Unformatted text preview: Note that the following lectures include animations and PowerPoint effects such as fly ins and transitions that require you to be in PowerPoint's Slide Show mode (presentation mode). The Family of Stars Chapter 9 Science is based on measurement, but measurement in astronomy is very difficult. Even with the powerful modern telescopes described in Chapter 6, it is impossible to measure directly simple parameters such as the diameter of a star. This chapter shows how we can use the simple observations that are possible, combined with the basic laws of physics, to discover the properties of stars. With this chapter, we leave our sun behind and begin our study of the billions of stars that dot the sky. In a sense, the star is the basic building block of the universe. If we hope to understand what the universe is, what our sun is, what our Earth is, and what we are, we must understand the stars. In this chapter we will find out what stars are like. In the chapters that follow, we will trace the life stories of the stars from their births to their deaths. Guidepost I. Measuring the Distances to Stars A. The Surveyor's Method B. The Astronomer's Method C. Proper Motion II. Intrinsic Brightness A. Brightness and Distance B. Absolute Visual Magnitude C. Calculating Absolute Visual Magnitude D. Luminosity III. The Diameters of Stars A. Luminosity, Radius, and Temperature B. The H-R Diagram C. Giants, Supergiants, and Dwarfs Outline D. Luminosity Classification E. Spectroscopic Parallax IV. The Masses of Stars A. Binary Stars in General B. Calculating the Masses of Binary Stars C. Visual Binary Systems D. Spectroscopic Binary Systems E. Eclipsing Binary Systems V. A Survey of the Stars A. Mass, Luminosity, and Density B. Surveying the Stars Outline Light as a Wave (1) We already know how to determine a star’s • surface temperature • chemical composition • surface density In this chapter, we will learn how we can determine its • distance • luminosity • radius • mass and how all the different types of stars make up the big family of stars. Distances to Stars Trigonometric Parallax: Star appears slightly shifted from different positions of the Earth on its orbit The farther away the star is (larger d), the smaller the parallax angle p. d = __ p 1 d in parsec (pc) p in arc seconds 1 pc = 3.26 LY The Trigonometric Parallax Example: Nearest star, α Centauri, has a parallax of p = 0.76 arc seconds d = 1/p = 1.3 pc = 4.3 LY With ground-based telescopes, we can measure parallaxes p ≥ 0.02 arc sec => d ≤ 50 pc This method does not work for stars farther away than 50 pc. Proper Motion In addition to the periodic back-and- forth motion related to the trigonometric parallax, nearby stars also show continuous motions across the sky....
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Chapter 09 - Note that the following lectures include...

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