1. Lunar Eclipse Feb 20 (Next Wednesday)!!!! Next Tuesday’s class will be devoted tothe moon and the eclipse. We’ll watch fromthe mall on Wednesday evening. No classnext Thursday - but there will be homeworkrelated to our lunar observations.2. Homework 2 is due now. Homework 3 willbe posted today, due Feb 21 (Thursday).2. Astrobiology Lecture Tonight3. Essay Topics due Today.AnnouncementsDate: !!!Tuesday February 12, 2008Time: !!!Lecture (7pm) followed by book signing (8pm)Place: !!Center for Creative Photography (UA Main Campus).Gregory Benford, Author and Astrophysicist at UC Irvine "Seeking Ozymandias: Building and Searching for Beacons”What would transmitters be like if built by civilizations with a variety ofmotivations, but who cared about cost? We have considered the physicallimitations a beacon builder would face in constructing extremely high powerradiators. Beacons built by distant advanced, wealthy societies may have verydifferent characteristics from what SETI researchers now seek.Very high powersystems have driving factors set by fundamental properties of materials, suchas cooling of such high powers. The Principle of Parsimony suggests thatbeacon will compete with other social goods, for altruistic reasons. SuchBeacons will have narrow beam widths, be pulsed and broadband, to minimizecosts. Therefore, the transmission strategy for a distant beacon may be a rapidscan of the galactic plane, to cover the angular space. Searches for suchintermittent, broadband signals could find signals we have neglected, becausewe believed earlier that the Beacon builders will be spendthrifts. Yet stablesocieties do not sacrifice their societies for distant others. Perhaps we shouldconsider long-term stability from a moral point of view.“Finally we shall place the Sun himself at the centerof the Universe. All this is suggested by thesystematic procession of events and the harmonyof the whole Universe, if only we face the facts, asthey say, ‘with both eyes open’ ” - Nicolaus Copernicus De Revolutionibus orbiumcoelestium“There was music in the cafes at night andrevolution in the air. ” - Bob DylanCopernicus (1473-1543) wasthe sun of a successfulmerchant in central Poland.Copernicus studied to be aphysician, which, at the timeincluded the study ofastronomy, because doctorsused astrology to decide ontreatments. Copernicus workedas a deacon in the Church andspent his time studyingAstronomy. He wrote the first draft of De Revoluitonibus in1513, but, because of worries about how it would bereceived, he delayed publication until 1543, when he was onhis death bed.What else was going on at the Beginning of the16th Century?• Europe was coming out of thedark ages, rediscovering Greekand Roman learning andexploring the world.• Explorers were sailing to Africa and Asia. Columbusdiscovered America while Copernicus was studying at theUniversity. Malgalhães (Magellan) circumnavigated theglobe. All this relied heavily on Astronomy.• Printing was becoming common. A man of modestmeans, like Copernicus, could own books. He had 2copies of the Almagest.• There was an explosion in artistic activity.Michelangelo’s “David”1501-1504da Vinci’s “Mona Lisa”1503-1506CopernicusCopernicus’’ Solar System Solar System From De Revolutionibus•The Sun is in the center•Simpler than Ptolemy’s Model(No need for epicycles)• Circular Orbits are assumed.This will be proved wrong.• More accurate? No, it hadabout the same accuracy.• Why would we prefer this modelto Ptolemy’s?Ptolemy’s Geocentric System, codifiedin the AlmagestThis is getting complicated.Figures from Astronomy Today by Chaisson and McMillanLink to movieOccam’s Razor“One should not increase, beyond what is necessary, thenumber of entities required to explain anything.”If you have two theories that are equally successful inexplaining a phenomenon, the simpler one is better.William of Ockham (1285-1349) was aFranciscan monk and philosopher whoespoused the virtues of simplicity andpoverty in science and in life.Suggesting that the Pope conform tothe latter got him excommunicated.The conviction of simplicity persists.Tycho Brahe (1546 – 1601)The discovery of a new starStellar Parallax• Tycho argued that thenew star must be in thecelestial sphere because itexhibited no parallax.• This discovery showedthat the heavens were notperfect and unchanging.25 Years of Planetary ObservationsTycho caught the attentionof King Frederick II ofDenmarkWith royal funds, he built theultimate observatory.He designed, & testedinstruments, compiling themost comprehensiveplanetary observations ever,with accuracy of 1°, about5x better than before.Uraniborg, Hvencomplete with wine cellar and prisonJohannes Kepler(1571-1630)Kepler joined Tycho a yearbefore Tycho’s death (1600).Assuming Tycho’s position,Kepler inherited the records ofTycho’s observations.From this Kepler knew thatplanets did not travel on circlesand devised a new way todescribe planetary motion.Kepler searched for a single physical explanation toplanetary motion – a force between planets and the Sun.*Influenced by William Gilbert’s De MagneteKepler aimed to explainTycho’s observations whichshowed that planets do notmove in circlesHe noted that planets closer tothe Sun in Copernicus’ modelmoved faster than thosefurther out.A force must therefore act.Kepler thought it wasmagnetic*Thus he believed that a simpleset of laws existed by which allplanets move.Kepler’s Three Laws1. Planets move about the Sun in elliptical orbitswith the Sun at one focus.2. The line joining a planet to the Sun sweepsover equal areas in equal intervals of time.3. The square of the time of one revolution of aplanet about the Sun is proportional to thecube of the orbit’s semimajor axis.1. Planets move inelliptical orbits withthe Sun at onefocus.2. The line joining the Sun to the planetsweeps equal areas in equal intervals oftime.Link to movie3. The square of a planet’s periodequals the cube of its semi-major axisP is the period, a is the semi-major axis, k is aconstant which depends on the units of P & a.(For P in years and a in Astronomical Units, k=1.)The farther a planet is from the Sun, the longer it’syearP2 = k · a3Simple Example of P2=a3• Consider a hypothetical planet orbiting thesun with a semi-major axis of 4 A.U.• Let a = 4 A.U. (Astronomical Units)• Then a3 = 43 A.U.3 = 64 A.U.3• P2 = 64 years2• P =
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