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James Bradley discovers the aberration of starlight. Bradley found that the positions of all the stars shift back and forth as part of an annual cycle caused by the motion of the Earth about the Sun.
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Newton publishes "Principia". Newton's monumental work described his discoveries about gravity, motion and the orbits of the planets. p. 80-86, F 2.2, F 2.3, F 2.4, F 2.5, F 2.6, F 2.7, F 2.8
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Edmund Halley predicts return of Comet Halley. Halley noted that comets with similar orbits had appeared in 1456, 1531, 1607, and 1682. He proposed that these were all the same comet and that it would return in 1758 or 1759 - which it did. p. 309-310, F 10.8, 10.9, 10.10
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Christian Huygens proposes that light consists of waves. Huygens's ideas were disputed by Newton, who proposed that light was mae up of a stream of particles. p. 96-97. F. 3.1, A3.1
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James Gregory makes the first realistic estimate of the distances of the stars. Gregory assumed that the other stars were just as bright as the Sun and then calculated how distant they had to be to match their apparent brightnesses. p. 356-358, F 12.1, F 12.2
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Dante describes medieval picture of universe in "Divine Comedy". Dante's picture of the universe has the Earth at its center, surrounded by the spheres of the Moon, Sun, planets, the fixed stars, a crystalline sphere and, finally, paradise.
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Roger Bacon advocates experimentation. Bacon was among the first to recommend experimentation as the best way to acquire scientific knowledge.
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Establishment of first universities in Europe. The development of astronomy was aided by the birth of universities at Bologna, Oxford, Paris, and a few other European cities.
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Chinese record supernova that produces Crab Nebula. Chinese astronomers observed a supernova that was visible in the daytime. The matter blasted outward by the supernova later became observable as the Crab Nebula. p. 140-141, Box F 4.5
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Ptolemy "perfects" geocentric model of solar system. In Ptolemy's model the planets moved on circles (epicycles) that moved on other circles (deferents). The model could accurately predict the positions of the planets. Ptolemy also compiled a catalog of stellar brightnesses based partly on the earlier catalog of Hipparchus. p. 45-46, F 1.25 p. 365-366
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Hipparchus discovers precession, prepares stellar catalog. Hipparchus compared his own observations with earlier ones to discover precession, the slow change in the direction of the Earth's polar axis. He also made what was probably the first catalog of the positions and brightnesses of the stars.
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Building of Bighorn Medicine Wheel. Plains Indians of North America built medicine wheels, monuments made of piles of stones. Alignments in the medicine wheels often pointed toward the direction of sunrise at the winter solstice.
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