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2) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: Our Home-The Milky Way Galaxy
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Starting a series of lectures on galaxies, you begin with our home galaxy, the Milky Way. The band of light by that name is simply the Galaxy seen edge-on from our place within it. You also explore the nebulae in our Galaxy, many of which are regions of stellar birth.
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A voyage to another star would require exact information on distances and properties of the stars. This lecture shows how astronomers measure the distance to nearby stars and how they determine their surface temperatures, which are the basis for stellar classification.
10) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: Jupiter and Its Amazing Moons
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Beyond Mars lie the four gas giants: Jupiter, Saturn, Uranus, and Neptune. Jupiter is the Solar System's largest planet by far. Its moons include Io, which is volcanically active, and Europa, which may have an ocean of liquid water below its frozen surface.
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According to general relativity, the fate of the Universe is tied to its global geometry. If the Universe has positive curvature, like a sphere, it must eventually collapse in a "Big Crunch." If it is flat or has negative curvature, however, it will expand forever.
12) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: Dark Energy-Quintessence?
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This lecture looks at problems with the quantum fluctuations explanation for dark energy. One alternative is called quintessence-a class of models that postulate repulsive energy that may be associated with unified forces or fields.
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If a quantum fluctuation gave rise to our Universe, must ours be the only one? Are others possible, perhaps even with different rules? This lecture examines reasons for suspecting the existence of other universes, though we do not know how to test for their presence.
15) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: The Afterglow of the Big Bang
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An accidental discovery in 1965 overturned the steady-state theory of the Universe, an alternative to the Big Bang theory. The detection of a uniform microwave glow in all directions was exactly what was expected if the Universe was hot and dense long ago.
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Brown dwarfs are low-mass objects whose dim glow is caused by slow gravitational contraction and the fusion of deuterium, a heavier but far less abundant isotope of hydrogen. Free-floating planets have even less mass than brown dwarfs and are not associated with any star.
20) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: Warping of Space and Time
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This lecture explores observational tests of general relativity. Astronomers exploit its effects by searching for distant objects that are gravitationally lensed, which occurs when an object's light is bent and focused by foreground masses such as galaxy clusters.
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