For thousands of years, humans have sought to understand the Universe of which they’re a part—its beginnings, structure, functioning, and future. Today, we term these studies cosmology. Many of the earliest ideas were fanciful, revolving around gods and goddesses, though there were also investigations of a more scientific nature. People asked the right questions, made careful observations of natural phenomena, used common sense and ingenuity, and came up with quite accurate answers to some basic yet profound questions. Human history and this chapter are both filled with many of these milestones of understanding. Included in this chapter are discussions of the following:

• the discovery that, unlike stars, planets are wanderers
• Ptolemy’s belief in an Earth-centered Universe
• Copernicus’s belief in a Sun-centered Universe
• Kepler’s work showing that planetary orbits are elliptical
• Galileo’s use of the telescope to study Earth’s distant neighbors
• Newton’s calculations about gravity and the laws of motion
• Eratosthenes’s calculations that gave Earth’s correct circumference
• Foucault’s analysis of pendulum motion to prove that Earth rotates (spins on its axis)
• the development of the concept of a light year to designate both distance and time in the Universe
• the discovery of galaxies, including our own Milky Way
• Doppler’s explanation of wavelengths and frequencies altered by moving sources
• the correlation between the Doppler effect and the red shift of the expanding Universe
• the big bang theory of the beginning of the Universe
• the realization that stars have beginnings, lifetimes, and deaths
• the realization that existing stars are of different ages, generations, sizes, temperatures, and densities
• the process of element formation in stars
• the development of our round Earth and our planetary system
• the origin of our Moon

The vastness of the Universe defies comprehension, so scientists created special units like the light year to make the mathematics about it more manageable, and frequently use analogies to help humans fathom its large-scale processes.

By chapter’s end you may feel you’ve had a crash course in ancient astronomy. In a way you have, but you also have established a firm foundation for your study of geology.

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