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AS101 Lecture 9

# AS101 Lecture 9 - AS101 Lecture 9 Logistics Do not forget...

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AS101 Lecture 9 Logistics: • Do not forget Night Lab • Homework: Read Chapters 3 and 4 Last Lecture: • Greek astronomy • Heliocentric universe • Ptolemy, Copernicus, Brahe Today’s Lecture: • Kepler • Galileo • Newton

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News Items: The NY Times New Planet May Be Able to Nurture Organisms By DENNIS OVERBYE Published: September 29, 2010
Johannes Kepler (1571-1630) Born 1571, in Weil, Germany to a poor Protestant family in a predominantly Catholic region Father unreliable, mercenary soldier Mother apparently unpleasant and unpopular - accused of witchcraft Never healthy as a child

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Ellipse
Some Details

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Kepler’s First Law Planetary orbits follow an ellipse with the sun at a focus
Kepler’s Second Law A planet moves along its orbit: • with a changing speed • a line from the planet to the Sun sweeps out equal areas in equal intervals of time

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Kepler’s Third Law A planet’s orbital period, p , relates to its average distance from the sun, a , by where a is the semimajor axis of the ellipse which is the average distance between the sun and planet. This means that For bodies orbiting the sun c is different for moons and other solar systems 3 2 a p 3 2 ca p 3 2 .) . /( ) ( 1 U A yr c
Check Kepler’s 3rd Earth: P = 1 (in year); a = 1 (in AU) so, P 2 = a 3 holds (whew!) Jupiter: a = 5.2 AU; P = sqrt (5.2 3 ) = 11.86 yrs Measured value = 11.86 years! Comet Haley, P = 76 years; a = 17.94 AU (CHECK)

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Relation between P and a
Kepler’s third law shown graphically. Top: a 3 Vs. P 2 is a straight line with no intercept! Bottom: a Vs P is not a straight line (non-linear)

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Lets look at the speed Sam Chen: Does Kepler’s 3 rd Law support Copernicus’ explanation of Retrograde motion?
Kepler’s Laws These are empirical laws which describe the planetary motions. While, revolutionary, they do not explain why this is so. They were arrived at after careful examination of highly accurate data - but changed 2,000 year old idea! We have to wait till we examine Newton’s Laws (another guy with three laws)

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Time Out to Think Question The sidereal period of a planet is eight years. What is its distance from the sun? 1. 2 AU 2. 4 AU 3. 8 AU 4. 16 AU 5. 64 AU 3 3 2 2 ) / 1 ( a AU yr p a a 4 64 64 ) / 1 ( ) 8 ( 3 3 3 3 3 2 2 Ashley Lisenby: Does apply for the moon going around Earth? 3 3 2 2 ) / 1 ( a p
Galileo Galilei (1564-1642) Father of Experimental Science Developed theory of motion and gravity Designed a pendulum clock Invented primitive thermometer First to use telescope in astronomy David Batuner: Who invented the telescope?

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Galileo Galilei (1564-1642) Born in Pisa (1564) 1581: University of Pisa (medicine, astronomy, math - reputation as “the wrangler”) Moved to Padova in 1592 (stayed till 1610) Radical idea - test theories with simple experiments - father of modern science 1608: Hans Lippershey invents the telescope http://galileo.imss.firenze.it/museo/b/eg a
Galileo (contd) 1609: Galileo started to use the telescope, which was used as a naval warfare tool for astronomical observations Earliest known illustration of a telescope (from a letter by

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AS101 Lecture 9 - AS101 Lecture 9 Logistics Do not forget...

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