Chapter 02

Chapter 02 - 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 Sky Chapter 2 Astronomy is about us. As we learn about astronomy, we learn about ourselves. We search for an answer to the question What are we? The quick answer is that we are thinking creatures living on a planet that circles a star we call the sun. In this chapter, we begin trying to understand that answer. What does it mean to live on a planet? The preceding chapter gave us a quick overview of the universe, and chapters later in the book will discuss the details. This chapter and the next help us understand what the universe looks like seen from the surface of our spinning planet. But appearances are deceiving. We will see in Chapter 4 how difficult it has been for humanity to understand what we see in the sky every day. In fact, we will discover that modern science was born when people tried to understand the appearance of the sky. Guidepost I. The Stars A. Constellations B. The Names of the Stars C. The Brightness of Stars D. Magnitude and Intensity II. The Sky and Its Motion A. The Celestial Sphere B. Precession III. The Cycles of the Sun A. The Annual Motion of the Sun B. The Seasons Outline IV. The Motion of the Planets A. The Moving Planets B. Astrology V. Astronomical Influences on Earth's Climate A. The Hypothesis B. The Evidence Outline (continued) Daily Motion in the Sky (SLIDESHOW MODE ONLY) Constellations In ancient times, constellations only referred to the brightest stars that appeared to form groups, representing mythological figures. Constellations (2) Today, constellations are well-defined regions on the sky, irrespective of the presence or absence of bright stars in those regions. Constellations (3) The stars of a constellation only appear to be close to one another Usually, this is only a projection effect . The stars of a constellation may be located at very different distances from us. Constellations (4) Stars are named by a Greek letter ( , , ) according to their relative brightness within a given constellation + the possessive form of the name of the constellation: Orion Betelgeuze Rigel Betelgeuse = Orionis Rigel = Orionis The Magnitude Scale First introduced by Hipparchus (160 - 127 B.C.): Brightest stars: ~1 st magnitude Faintest stars (unaided eye): 6 th magnitude More quantitative: 1 st mag. stars appear 100 times brighter than 6 th mag. stars 1 mag. difference gives a factor of 2.512 in apparent brightness (larger magnitude => fainter object!) Betelgeuse Rigel Magnitude = 0.41 mag Magnitude = 0.14 mag The Magnitude Scale (Example) Magn. Diff. Intensity Ratio 1 2.512 2 2.512*2.512 = (2.512) 2 = 6.31 5 (2.512) 5 = 100 For a magnitude difference of 0.41 0.14 = 0.27, we find an intensity ratio of (2.512) 0.27 = 1.28. The Magnitude Scale (2) Sirius (brightest star in the sky): m v = -1.42 Full moon: m...
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Chapter 02 - Note that the following lectures include...

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