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Introduction to Astronomy. Ancient cultures, early astronomers and how we got to what we know today. What is a day?. What they saw: The time it takes the sun to cross the sky and return to the same point. What they thought: That the sun revolved around the Earth once each day
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Introduction to Astronomy Ancient cultures, early astronomers and how we got to what we know today.
What is a day? What they saw: • The time it takes the sun to cross the sky and return to the same point. What they thought: • That the sun revolved around the Earth once each day What we know: • The time required for the Earth to rotate once on its axis.
What is a month? What they saw: • The amount of time required for the moon to move through a complete set of phases. What they thought: • The Earth cast a shadow on the moon, creating the phases as the moon revolved around the Earth What we know: • The amount of time it takes the moon to revolve around the Earth. Phases are a result of the Earth, Moon, Sun System.
What is a year? What they saw: • The time it takes for a group of stars (constellation) to return to the same part of the sky at a certain time of day. What they thought: • The time it takes for the sphere of stars surrounding the Earth to spin around once. What we know: • Time required for the Earth to revolve around the sun.
Early Observers: The beginnings of Astronomy Scientists have found evidence for ancient astronomical activities from across the world.
Nabta • Southern Egypt- Some stones are positioned such that they would have lined up with the sun during the summer solstice 6,000 years ago.
Stonehenge • Another ancient site that was probably used to make observations of the sky. • Stones are arranged primarily in circles which are aligned with the sunrise during the summer and winter solstices. • Built over a period of 1,500 years. • Built for ceremony and rituals.
Babylonians • Ancient empire located in present-day Iraq • 700 B.C. to A.D. 50, Babylonians precisely tracked the positions of the planets and moon. • Skilled at forecasting the movements of these celestial bodies, which enabled them to make an accurate calendar.
Ancient Chinese • 1,000 B.C. could predict eclipses. • The Chinese named 800 stars by 350 B.C. • The Chinese skillfully tracked and predicted the same motions in the sky as the civilizations that influenced Western astronomy.
Ancient Greeks • Learned to observe the sky to keep track of time. • Helped make astronomy a true science. • Aristotle (Greek philosopher) successfully explained the phases of the moon. • Correctly stated that Earth was a sphere
Ancient Arabs • Followed Greeks and Romans. • Used Greeks’ knowledge of astronomy to develop astronomy while Europe fell into the “Dark Ages” • Many stars have Arabic names because of this period. • Invented astrolabe, algebra and modern number system.