Please turn on your clickersASTRONOMY 103The Evolving UniverseVan Vleck B130 MW, 1:20-2:10pm• Professor: Andy Sheinis [email protected]• Office: 5520 Sterling Hall• Phone: 262-0492• Office Hours:Tu 2pm-3pm, Wed 3pm-4pm••• TA: Ella Braden [email protected]• Office: 4514 Sterling Hall• Phone: (608) 265-2554• Office Hours:• Monday: 11:45-1:15• Wednesday: 11:00-12:30• Thursday: 1:45-3:15• Friday: 11:00-12:30• Sunday 8:00-9:00pm online office hour•ASTRONOMY 103The Evolving Universe• Text: "Pathways to Astronomy" Schneider and Arny, McGraw-Hill (withthe clickers and Starrynight observing program).••• Clickers: We will use the clickers for this class. Clickers are available withthe text or separately at the UW Bookstore. They must be registeredonline at www.einstruction.com before you can use them in class. Theregistration code for the class is Class Key: F37866 N695.Directions for registering the clickers are attached as well as a tutorial.• Website: http://www.astro.wisc.edu/~sheinis/103course.htm• See the website for HW assignments, solutions and interesting astronomyWhy is it impossible toprove a theory?A. A theory is not a fact. Only facts can be proven.B. * A theory is only supported by observations, a singlecontrary observation can disprove it.C. Theories can be proven! Once it is proven it is called afact.D. It is not possible for humans to observe evrything aboutthe universe, if they could they could prove a theory.(this one can also be argued as true)HypothothesisTheory or LawTests/observations Models/predictionsFacts/observablesPreview of Planetarium workUnits 5 and 6The Celestial Sphere I• Stars in the universe are located atvarious distances from Earth, butcan be imagined as lying on asphere, with the Earth at its center.• This sphere appears to rotatearound the Earth, giving theimpression that stars rise and set.• Since earliest times, humans have sought tounderstand the night sky• A useful model of the sky is called theCelestial Sphere• It is not real – it is simply a tool forunderstanding and predictionThe Celestial Sphere II• Important Terms– Zenith: The point directly overhead on thecelestial sphere (CS)– Nadir: The point opposite the zenith on the CS– North or south celestial pole: The point aroundwhich the stars appear to rotate– Celestial Equator: An extension of the Earth’sequator expanded out to the surface of the CS.– Horizon: The lower edge of the visible CSSkywatching• Under dark skies, you can seethousands of stars. There are somestars and constellations, however, thatyou can only see from northern orsouthern latitudes• In the northern hemisphere,constellations that never set (butsimply circle around the North Celestialpole) are called circumpolarconstellations• Skywatchers at your latitude in thesouthern hemisphere never see yourcircumpolar stars!Constellations and Asterisms• The human mind is very good atrecognizing patterns –consequently we have foundand named patterns of stars onthe celestial sphere• The names of these patternshave their origins in mythologyfrom all over the globe• Sometimes very hard to see!• These patterns are calledconstellations– 88 internationally recognizedconstellations, covering the entiresky– Star names frequently include thename of the constellation in whichthey are located• Some popular patterns are notconstellations – these are calledasterisms– The Big Dipper is an asterism withinUrsa Major.The Annual Motion of the Sun• As the Earth revolves around(orbits) the Sun, the Sunappears to move through 13constellations on a belt aroundthe celestial sphere called theecliptic• When the sun’s glare blocks aparticular constellation fromview, we say that the Sun is“in” that constellation• As this motion repeats itselfafter one year, it is called theSun’s annual motion• The motion of the stars isrecorded as sidereal time• Sidereal day is 1/356 shorterthan a solar day (4 minutes).TaurusLeoOphiucusPiscesThe Motion of the Planets• Because the planets’orbits all lie in more orless the same plane,the paths of theplanets through thesky all lie close to theecliptic, appearing tomove through theconstellations of thezodiac• Only Pluto seems tomove far from theeclipticGeocentric Models• Models in which everythingrevolves around the Earthare called Geocentricmodels.• From earliest Greek times,this kind of model was usedto describe the heavens• Planets and stars residedon their own spheres, eachtipped slightly relative toeach other. Thisreproduced the motion ofthe planets and Sunthrough the sky.• Did not explain retrogrademotion!Heliocentric vs. GeocentricViewJohannes Kepler (1571-1630)• Using Tycho Brahe’s data, discovered thatplanets do not move in circles around theSun, rather, they follow ellipses with the Sunlocated at one of the two foci!Kepler’s First Law• Planets move in ellipticalorbits with the Sun at onefocus of the ellipse– Developed a heliocentric(Sun-centered) model– Did not agree with theancients (or Brahe!)– The shape of the ellipse isdescribed by its semi-major and semi-minoraxes.Kepler’s Second Law• The orbital speed of aplanet varies so that a linejoining the Sun and theplanet will sweep out equalareas in equal timeintervals• That is, planets movefaster when near the Sun,and slower when fartherfrom the Sun• Explained the non-circularbehavior of the planets!Kepler’s Third Law• The amount of time a planet takesto orbit the Sun (its period) P isrelated to its orbit’s size, a, byP2 = a3• Kepler’s Laws describe the shapeof a planet’s orbit, its orbitalperiod, and how far from the Sunthe planet is positioned.• These were empiricalrelationships, found fromobservation rather than the logicof the ancients.Kepler's 3d law (that the period squared isproportional to the semi-major axis cubed) doesNOT apply to the motion of: a) a satellite around the Earth b) a comet around the Sun c) one star about another in a binary starsystem d) one galaxy about another e) all of the above