Alex Filippenko
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Why is the sky dark at night? In an infinitely old and large Universe the sky should be ablaze with light at all times. There are several possible answers to this paradox, each of which has profound cosmological implications. The relative youth of the Universe is now known to be the main explanation.
6) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: The Corpses of Massive Stars
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The imploding core of a Type II supernova typically forms a bizarre, enormously compact object called a neutron star, consisting entirely of tightly packed neutrons, a teaspoon of which would weigh about a billion tons.
9) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: The Diverse Sizes of Stars
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This lecture discusses the Hertzsprung-Russell diagram, a plot of stellar surface temperature versus luminosity that contains a wealth of information. Stars spend most of their existence on the diagram's well-defined main sequence; outliers include supergiants and white dwarfs.
10) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: Our Sun, the Nearest Star
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Beginning a sequence of lectures on the Solar System, you start with the Sun, which you explore from the interior to the surface. Sunspots are cooler regions associated with strong magnetic fields, and violent eruptions blast solar material into space.
12) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: The Quest for Black Holes
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Because they don't emit any light, black holes can't be seen directly. But they reveal their presence through their gravitational influence on other objects. This lecture looks at the methods astronomers use to track them down.
14) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: A Grand Tour of the Cosmos
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You embark on a fantastic voyage throughout the Universe, starting in this lecture with a whirlwind tour of the course, which extends from phenomena in Earth's atmosphere to events at the farthest reaches of space and time.
16) Understanding the Universe: An Introduction to Astronomy, 2nd Edition: On the Shoulders of Giants
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According to legend, Newton saw a falling apple and realized that the force that pulled it toward Earth also pulled on the Moon, keeping it in its orbit. Building on the work of Kepler and Galileo, he revolutionized astronomy with his law of universal gravitation and laws of motion.
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Apparent brightness is the observed brightness of a star. Because stars are at different distances, astronomers need a standard reference by which to compare stars in absolute terms, as if they're all at the same distance. This standard is called intrinsic brightness, or luminosity.