A1 01 History and Concepts
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A1 01 History and Concepts

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Prof. Miller's Astronomy 1 lecture notes on the History & Concepts of Astronomy

Prof. Miller's Astronomy 1 lecture notes on the History & Concepts of Astronomy

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    A1 01 History and Concepts A1 01 History and Concepts Presentation Transcript

    • Early Astronomers LACC Ch. 1 (§1.4) • Earth: Shape and Size? • Solar System: Geocentric or Heliocentric? • Galileo Galilei Astronomy is the branch of science concerned with the nature of space, e.g. stars, planets, the universe. Monday, February 8, 2010 1
    • The Earth is (mostly) Round In fact, the Earth is a Oblate Spheroid--it bulges slightly at the equator. Who first discovered that the Earth is round? When? Monday, February 8, 2010 2
    • The Earth is Round On the Heavens By Aristotle Written 350 B.C.E Translated by J. L. Stocks ...the interposition of the earth that makes the eclipse, the form of this line will be caused by the form of the earth's surface, which is therefore spherical. Again, our observations of the stars make it evident, not only that the earth is circular, but also that it is a circle of no great size. For quite a small change of position to south or north causes a manifest alteration of the horizon. There is much change, I mean, in the stars which are overhead, and the stars seen are different, as one moves northward or southward. http://classics.mit.edu/Aristotle/heavens.2.ii.html Monday, February 8, 2010 3
    • Size of the Sun Aristarchus of Samos (310-230 BC) also reasoned that since the Sun and the Moon have the same angular size, but the Sun is 19 times further (it is actually 390 times), then the Sun must be 19 times bigger than the Moon. http://www.astro.cornell.edu/academics/courses/astro201/aristarchus.htm Monday, February 8, 2010 4
    • The Earth is Round Eratosthenes about 240 BC At Syene, the elevation of the sun was 90°; at Alexandria it was about 7 87°. Eratosthenes concluded, using geometry of parallel lines, that the distance from Alexandria to Syene must be 7/360 of the total circumference of the Earth. The distance between the cities was known from caravan travellings to be about 5,000 stadia...which implies a circumference of 252,000 stadia. It is generally believed that Eratosthenes' value corresponds to between 39,690 km and 46,620 km. The circumference of the Earth around the poles is now measured at around 40,008 km. http://www.astro.cornell.edu/academics/courses/astro201/eratosthenes.htm Monday, February 8, 2010 5
    • Geocentric Model Claudius Ptolemaeus’s Almagest in c. 140 A.D. Because the planets seem to move backward some of the time, however, their observed motion cannot be explained by single circles. Ptolemy adopted a solution to this problem that he attributes to Apollonius (although earlier Greek writers, such as Hipparchus, also used this concept): Each planet moves on a small circle, called an epicycle.... Although these complex motions seem strange to those familiar with modern astronomy, they succeed in accounting for observed motions. http://www.answers.com/topic/almagest?cat=technology Monday, February 8, 2010 6
    • Heliocentric Model Nicolás Copérnic’s De Revolutionibus Orbium Coelestium in 1543. De Revolutionibus famously proposed the heliocentric theory: the (now taken for granted) proposition that the Earth rotates around the Sun rather than vice versa. During Copernicus’ lifetime, orthodox opinion asserted the contrary view – that the Earth was fixed, unmoving at the centre of the Universe. This “geo-centric” myth was not easy to de-bunk: it was popularly held to be true by common sense perception supported by two millennia of philosophical tradition.... http://special.lib.gla.ac.uk/exhibns/month/apr2008.html Monday, February 8, 2010 7
    • Retrograde Motion According to Geocentric Model http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/ marsorbit.swf&movieid=marsorbit&width=825&height=550&version=6.0.0 According to Heliocentric Model http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/ retrograde.swf&movieid=retrograde&width=700&height=600&version=6.0.0 Monday, February 8, 2010 8
    • Galileo Discovers Four Moons Around Jupiter Galileo first observed the moons of Jupiter on January 7, 1610 through a homemade telescope. He originally thought he saw three stars near Jupiter, strung out in a line through the planet. The next evening, these stars seemed to have moved the wrong way, which caught his attention. Galileo continued to observe the stars and Jupiter for the next week. On January 11, a fourth star (which would later turn out to be Ganymede) appeared. After a week, Galileo had observed that the four stars never left the vicinity of Jupiter and appeared to be carried along with the planet, and that they changed their position with respect to each other and Jupiter. Finally, Galileo determined that what he was observing were not stars, but planetary bodies that were in orbit around Jupiter. This discovery provided evidence in support of the Copernican system and showed that everything did not revolve around the Earth. http://www.telescope1609.com/ http://www.solarviews.com/eng/galdisc.htm Galileo.htm Monday, February 8, 2010 9
    • Galileo Discovers Four Moons Around Jupiter Galileo Galilei’s Sidereus Nuncius, March 1610. http://www.solarviews.com/eng/galdisc.htm Monday, February 8, 2010 10
    • Galileo: Phases of Venus Possibly the most compelling argument Galileo made in favor of the Heliocentric Universe of Copernicus was based on the observations of Venus. Galileo observed the phases of Venus throughout the year. At times Venus presented a small but circular disk and at other times a large crescent. Based on these facts as illustrated in his drawings in Sidereus Nuncius, Galileo reasoned that Venus must orbit the Sun; proof of the Copernican Universe. http://www.telescope1609.com/Galileo.htm Monday, February 8, 2010 11
    • Phases of Venus According to Geocentric Model http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/ ptolemaic.swf&movieid=ptolemaic&width=900&height=660&version=6.0.0 According to Heliocentric Model http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/ venusphases.swf&movieid=venusphases&width=870&height=600&version=6.0.0 Monday, February 8, 2010 12
    • Early Astronomers LACC Ch. 1 (§1.4) • Earth: Shape and Size? • Round--Aristotle, 350 BC • About 12756.32 kilometers or 7926.41 miles--Eratosthenes, about 240 BC • Solar System: Geocentric or Heliocentric? • Geocentric--Ptolemy, 140 AD • Heliocentric--Copernicus, 1543 AD • Galileo Galilei: Moons of Jupiter, Phases of Venus Monday, February 8, 2010 13
    • AstroTeam Classwork • Give four ways to demonstrate that the Earth is round. (Voyages, Ch. 1, pp. 40-41: 4) All classwork due presently. Monday, February 8, 2010 14
    • LACC: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 1, pp. 40-41: 1. Due at the beginning of the next class period. Monday, February 8, 2010 15
    • Physical Concepts LACC Ch. 2 (§2.1, 2.3) • Some basic Astronomy terminology • Kepler’s laws of planetary motion (1609) • Newton’s three laws of motion, Newton’s universal law of gravity (1687) Astronomy is the branch of science concerned with the nature of space, e.g. stars, planets, the universe. Monday, February 8, 2010 16
    • Astronomy Basics • star • solar system • planet • galaxy • moon (or satellite) • universe • asteroid • rotation (spin) • comet • revolution (orbit) Monday, February 8, 2010 17
    • Welcome to Astronomy 1 Discussion: What questions does Astronomy seek to answer? Monday, February 8, 2010 18
    • Kepler’s Laws of Planetary Motion 1. The orbit of a planet about the Sun is an ellipse with the Sun at one focus. 2. A line joining a planet and the Sun sweeps out equal areas in equal intervals of time. 3. The squares of the periods of the planets are proportional to the cubes of their semi-major axes (i.e. orbital radiuses): paraphrased from Johannes Kepler's Astronomia Nova and Harmonices Mundi published in 1609 and 1619. Monday, February 8, 2010 19
    • Kepler’s Laws of Planetary Motion Planet P (yr.) a (AU) T2 R3 Mercury 0.24 0.39 0.06 0.06 Venus 0.62 0.72 0.39 0.37 Earth 1 1 1 1 Mars 1.88 1.52 3.53 3.51 Jupiter 11.9 5.2 142 141 Saturn 29.5 9.54 870 868 Monday, February 8, 2010 20
    • Kepler’s Laws of Planetary Motion http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/ kepler.swf&movieid=kepler&width=900&height=710&version=6.0.0 Monday, February 8, 2010 21
    • Newton’s Laws of Motion 1. An object at rest remains at rest, and an object in motion remains in motion, unless acted upon by on outside force. (aka: The Law of Inertia) 2. A force causes a mass to accelerate. (aka: F = ma) 3. For every action, there is an equal and opposite reaction. paraphrased from Isaac Newton’s Philosophiæ Naturalis Principia Mathematica published in 1687. Monday, February 8, 2010 22
    • Newton's law of universal gravitation F = Force G = a constant: 6.67 x 10-11 m3/(kg•s2) M’s = two masses R = distance between the two masses Monday, February 8, 2010 23
    • Newton's law of universal gravitation http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/circles/u6l3c.html Monday, February 8, 2010 24
    • Newton's law of universal gravitation http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/circles/u6l3c.html Monday, February 8, 2010 25
    • Newton + Kepler M a M = mass of central object a = radius of orbit p = period of orbit, i.e. how This equation is an long it takes to orbit once approximation. It works π = pi, 3.14 when the mass of the orbiting object is much less G = Gravitational constant, than the mass of the central 6.67 x 10-11 m3/(kg•s2) object. http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/circles/u6l3c.html Monday, February 8, 2010 26
    • Physical Concepts LACC Ch. 2 (§2.1, 2.3) • Some basic Astronomy terminology • rotation vs revolution • solar system vs galaxy vs universe • Kepler’s laws of planetary motion (1609) • Newton’s three laws of motion, Newton’s universal law of gravity (1687) Monday, February 8, 2010 27
    • AstroTeam Classwork • The International Space Station orbits about 500 km above the surface of the earth. (The Earth’s radius is 6378 km). How does the force of gravity in the I.S.S. compare with that on the ground? (Voyages, Ch. 2, pp. 58-59: 8) All classwork due presently. Monday, February 8, 2010 28
    • LACC: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 2, pp. 58-59: 11. • Ch 3: Tutorial Quizzes accessible from: www.brookscole.com/cgi-brookscole/course_products_bc.pl? http:// fid=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of the next class period. Monday, February 8, 2010 29