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. 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 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. 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. 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 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. 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. 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. 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. 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. 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. 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. 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 over a period of 1,500 years. Built for ceremony and rituals. Built for ceremony and rituals.

Babylonians Ancient empire located in present-day Iraq Ancient empire located in present-day Iraq 700 B.C. to A.D. 50, Babylonians precisely tracked the positions of the planets and moon. 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. 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. 1,000 B.C. could predict eclipses. The Chinese named 800 stars by 350 B.C. 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. 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. Learned to observe the sky to keep track of time. Helped make astronomy a true science. Helped make astronomy a true science. Aristotle (Greek philosopher) successfully explained the phases of the moon. Aristotle (Greek philosopher) successfully explained the phases of the moon. Correctly stated that Earth was a sphere Correctly stated that Earth was a sphere

Ancient Arabs Followed Greeks and Romans. Followed Greeks and Romans. Used Greeks’ knowledge of astronomy to develop astronomy while Europe fell into the “Dark Ages” Used Greeks’ knowledge of astronomy to develop astronomy while Europe fell into the “Dark Ages” Many stars have Arabic names because of this period. Many stars have Arabic names because of this period. Invented astrolabe, algebra and modern number system. Invented astrolabe, algebra and modern number system.