Introduction to AstronomyIntroduction to Astronomy

Ancient cultures, early Ancient cultures, early astronomers and how we got to astronomers and how we got to

what we know today.what we know today.

What is a day?What is a day?

What they saw:What they saw: The time it takes the sun to cross the sky and The time it takes the sun to cross the sky and

return to the same point.return to the same point.What they thought:What they thought:

• That the sun That the sun revolvedrevolved around the Earth once around the Earth once each dayeach day

What we know:What we know: The time required for the Earth to The time required for the Earth to rotaterotate once on once on

its axis.its axis.

What is a month?What is a month?What they saw:What they saw: The amount of time required for the moon to move The amount of time required for the moon to move

through a complete set of phases.through a complete set of phases.What they thought:What they thought: The Earth cast a shadow on the moon, creating the The Earth cast a shadow on the moon, creating the

phases as the moon revolved around the Earthphases as the moon revolved around the EarthWhat we know:What we know: The amount of time it takes the moon to revolve The amount of time it takes the moon to revolve

around the Earth. Phases are a result of the Earth, around the Earth. Phases are a result of the Earth, Moon, Sun System.Moon, Sun System.

What is a year?What is a year?

What they saw:What they saw: The time it takes for a group of stars (constellation) The time it takes for a group of stars (constellation)

to return to the same part of the sky at a certain to return to the same part of the sky at a certain time of day.time of day.

What they thought:What they thought: The time it takes for the sphere of stars surrounding The time it takes for the sphere of stars surrounding

the Earth to spin around once.the Earth to spin around once.What we know:What we know: Time required for the Earth to revolve around the Time required for the Earth to revolve around the

sun.sun.

Early Observers: The beginnings Early Observers: The beginnings of Astronomyof Astronomy

Scientists have found evidence for ancient Scientists have found evidence for ancient astronomical activities from across the astronomical activities from across the world.world.

NabtaNabta

Southern Egypt- Some stones are Southern Egypt- Some stones are positioned such that they would have lined positioned such that they would have lined up with the sun during the summer solstice up with the sun during the summer solstice 6,000 years ago.6,000 years ago.

StonehengeStonehengeAnother ancient site that was probably Another ancient site that was probably

used to make observations of the sky.used to make observations of the sky.Stones are arranged primarily in circles Stones are arranged primarily in circles

which are aligned with the sunrise during which are aligned with the sunrise during the summer and winter solstices.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.

BabyloniansBabyloniansAncient empire located in present-day IraqAncient empire located in present-day Iraq700 B.C. to A.D. 50, Babylonians precisely 700 B.C. to A.D. 50, Babylonians precisely

tracked the positions of the planets and tracked the positions of the planets and moon.moon.

Skilled at forecasting the movements of Skilled at forecasting the movements of these celestial bodies, which enabled these celestial bodies, which enabled them to make an accurate calendar.them to make an accurate calendar.

Ancient ChineseAncient Chinese1,000 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 The Chinese skillfully tracked and

predicted the same motions in the sky as predicted the same motions in the sky as the civilizations that influenced Western the civilizations that influenced Western astronomy.astronomy.

Ancient GreeksAncient GreeksLearned to observe the sky to keep track Learned to observe the sky to keep track

of time.of time.Helped make astronomy a true science.Helped make astronomy a true science.Aristotle (Greek philosopher) successfully Aristotle (Greek philosopher) successfully

explained the phases of the moon.explained the phases of the moon.Correctly stated that Earth was a sphereCorrectly stated that Earth was a sphere

Ancient ArabsAncient ArabsFollowed Greeks and Romans. Followed Greeks and Romans. Used GreeksUsed Greeks’’ knowledge of astronomy to knowledge of astronomy to

develop astronomy while Europe fell into develop astronomy while Europe fell into the the ““Dark AgesDark Ages””

Many stars have Arabic names because of Many stars have Arabic names because of this period.this period.

Invented astrolabe, algebra and modern Invented astrolabe, algebra and modern number system.number system.