PHYS40 Lecture 2

PHYS40 Lecture 2 - Lecture # 2: Development of Modern...

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Lecture # 2: Development of Modern Astronomy Sep-27-11 1
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Sep-27-11 2 Outline • The ancient root of astronomy • History of development of astronomy from ancient Greek • The Copernican revolution • Kepler’s laws of motion • Galileo’s discovery of the Earth’s motion and phases of Venus • Development of the present picture of the Cosmos
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Sep-27-11 3 Introduction Astronomy is the oldest of all sciences. Today, we know details about our planet, our Sun, our Galaxy and the Universe. Most of this knowledge were acquired over the last few centuries It all started at the time of ancient Greek 2000 years ago, continuing to the Copernican revolution 450 years ago, overturning the idea that the Earth was at the center of the Universe
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Sep-27-11 4 • Ancient people in central Africa predicted the rainfall by observing crescent of the Moon relative to the horizon • The orientation depends on the relative positions of the Sun and the Moon along the ecliptic, which varies with the time of the year
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Sep-27-11 5 Orientation of Crescent Moon with respect to horizon was used to predict rainy season in central Nigeria Oldest Astronomical Record: Ishango (animal bone) depicting lunar calendar from about 6500 BC Egyptians (2000 BC) divided daylight into 12 equal parts. Summer “hours” longer than winter “hours”. By about 1500 BC Egyptians used “water clocks. Hour glasses using sand were invented in 8th century AD.
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Sep-27-11 6 Astronomical Time • The origin of our modern clock is traced back to ancient Egypt, dividing the daylight into 12 equal parts. • The time was divided into ante meridiem (am) and post meridiem (pm)- (before and after the middle of the day)
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Sep-27-11 7 Observatories in the Americas Big Horn Medicine Wheel in Wyoming-built by Plains Indians. Originally thought that spokes aligned with risings and settings of Sun and other stars. Further investigation showed this not true. Sun Dagger in New Mexico-Rocks shape Sun’s light into dagger with a spiral carved on the rock. Dagger pierces spiral each year at noon on summer solstice. Caracol Mayan temple (1000 AD) in Mexico- many windows aligned with astronomical events.
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Sep-27-11 8 Stonehenge-Salisbury Plain in England • About 2800 BC to 1100 BC • Stone Age and Bronze Age • Druids • Astronomical Observatory
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Sep-27-11 9 Stonehenge
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Sep-27-11 10 Templo Mayo- Mexico city • Spectacular structure used to mark the seasons. The twin temple is located on a fat-topped 1500 Foot pyramid. • On the equinox, the Sun rose through the notch between the temples
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Sep-27-11 11 Sidereal (wrt stars) and Synodic (wrt sun) Periods Solar Day --> 24 h 00 m (time required for Sun to transit observer’s meridian on successive days) Sidereal Day--> 23 h 56 m (time required for star to transit observer’s meridian on successive days) To star AM: ante (before) meridian PM: post meridian
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Sep-27-11 12 Lunar Months Synodic Month-29.5 days Sidereal Month-27.3 days 30 O
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Sep-27-11 13 Days of the Week
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PHYS40 Lecture 2 - Lecture # 2: Development of Modern...

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