Exploring the Sphere
Exploring the Sphere
This chapter introduces the reader to the celestial sphere, or the Earth's surface. By rotating the sphere, the motions of the heavens can be simulated. There are three features of celestial motion that came to be associated with Aristotle: all objects move in circles; they travel at constant speeds on those circles; the Earth is at the center of the celestial sphere. The chapter shows how the movements of stars and planets on the sphere's surface can be determined by setting up a system of equatorial coordinates. It also explains how the celestial sphere can be set in motion through the day, and how Hipparchus of Rhodes endeavored to determine the eccentricity of the Sun's orbit. Finally, it discusses spherical geometry, with emphasis on finding bounds on the sides and angles of a spherical triangle.
Keywords: celestial sphere, Earth, celestial motion, stars, planets, equatorial coordinates, Hipparchus of Rhodes, Sun, spherical geometry, spherical triangle
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