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Astronomy & Astrophysics
Michael Reid

Chapter 3: The Science of Astronomy 3.1 The Ancient Roots of Science - Began in central Africa, where people long ago learned to predict the weather with reasonable accuracy by making careful observations of the Moon - The length of our day is the time it takes the Sun to make one full circuit of the sky - The length of a month comes from the moon’s cycle of phases, and our year is based on the cycle of the seasons - 7 days of the week were named after the seven naked-eye objects that appear to move among the constellations: the sun, the moon, and the five planets recognized in ancient times - Ancient societies studied the sky by: 1. Determining the time of day  Egyptians divided the daylight and night into 12 equal parts 2. Marking the Seasons  Stonehenge was both an astronomical device for keeping track of the seasons and a social and religious gathering place  Other structures were used to mark the sun’s position on special dates such as the winter or summer solstice 3. Lunar calendars  The 19-year cycle on which the dates of lunar phases repeat is called the Metonic cycle 4. Ancient structures and archaeoastronomy  The study of ancient structures in search of astronomical connections is called archaeoastronomy 5. From observations to science 3.3 The Copernican Revolution - Origin of modern science - Nicholas Copernicus, Tycho Brahe, Johannes Kepler challenged the prevailing dogma that our planet must be the center of the universe Copernicus - Born in Torun, Poland, on February 19, 1473 - First-class education in mathematics, medicine, and law - Sun-centered idea first proposed more than 1700 years earlier - Discovered simple geometric relationships that allowed him to calculate each planet’s orbital period around the Sun and its relative distance from the Sun in terms of the Earth- Sun distance - First printed copy of his book De Revolutionibus Orbium Coelestium (“Concerning the Revolutions of the Heavenly Spheres”) on May 24, 1543 - Overthrew the idea of earth-centered - Held fast to the ancient belief that heavenly motion must occur in perfect circles. This incorrect assumption forced him to add numerous complexities to his system - His complete model was no more accurate and no less complex than the Ptolemaic model Tycho - Danish nobleman - Alignment of Jupiter and Saturn occurred nearly 2 days later than the date Copernicus had predicted - Set about compiling careful observations of stellar and planetary positions in the sky - Observed nova, meaning “new star” in 1572 - Proved that the nova was much farther away than the Moon - Over a period of 3 decades, Tycho and his assistants compiled naked-eye observations accurate to within less than 1 arcminute - Advocated a model in which the Sun orbits Earth while all other planets orbit the Sun - Failed to explain the motions of the planets Kepler - German astronomer - Believed that planetary orbits should be perfect circles - Foun
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