Cosmology(and(the(Birth(of(Earth(="Where(do(we(come(from?(="Where(do(we(fit(in(the(Universe?(="Why(are(we(here?(Cosmology(• Study"of"the"structure"and"evolution"of"the"universe"• Cosmology"is"a"complicated"science"• Requires"thinking"in"unfamiliar"scales"of"space"and"time"• Spatial"Scales"• ;Attometers"(10;21"meters"to";10s"of"billions"of"light"years"(9.4622"meters"+)"• Temporal"scales";attoseconds"(10;21"seconds)"to";10s"of"billions"of"years"(3.1517"seconds"+"Earth"changing"place"• 3,000"years"ago,"humans"knew"the"heavens"well"• Stars"were"fixed"relative"to"other"stars"• Stars"moved"predictably"across"the"sky"• They"saw"retrograde"motion"separating"planets"from"stars"• They"did"not"think"of"Earth"as"a"planet,"however""• Movement"in"the"heavens"was"attributed"to"deities"An"evolving"image"of"Earth""• The"ancients"thought"the"universe"was"geocentric"• Heavenly"bodies"circle"around"a"motionless"central"geocentric"• Proven"by"Ptolemy,"the"idea"was"still"wrong"• Yet"it"held"as"doctrine"for"1,400"years"during"the"dark"ages"• It"became"religious"dogma"supporting"the"importance"of"Earth"in"the"Scheme"of"heaven""The"Renaissance"• A"rebirth"of"rational"thinking"in"15th"century"Europe""• Galileo"–observed"moons"orbiting"Jupiter"• Copernicus;"published"evidence"for"heliocentricity"• Kepler;his"elliptical"planetary"orbits"refuted"Ptolemy""Heliocentric"ideas"• Earth"didn’t"center"the"universe"• Planetary"orbits"weren’t"circular"• Not"all"bodies"orbited"earth"• Planes,"including"earth"orbit"the"sun""The"enlightenment"• Sir"Isaac"Newton"devised…."• The"law"of"universal"gravitation""• The"three"laws"of"motion"• The"mathematics"of"change"(calculus)"• He"proved"that"natural"law"governs" natural"events"• Geocentricity"faded"away"Earth"as"a"sphere"• A"flat"was"dispelled"by"250"BCE"• Abundant"evidence"suggested"a"spherical"earth"• A"curved"shadow"crossed"the"moon"during"eclipses"• Only"the"tops"of"distant"sailings"ships"were"visible"• In"1520,"Magellan"circumnavigated"this"sphere"A"flat"earth"will"receive"light"at"a"right"angle"at"noon"everywhere"during"summer"solstice"A"round"Earth"will"receive"light"at"diminishing"angles"toward"the"poles"at"noon"during"summer"solstice"Eratosthenes"measured"Earth"to"be"252,000"(Egyptian)"Stadia"or"39,630km"in"circumference"1%"error!"Earth"Rotation"How"do"we"know"that"Earth"Rotat es"• Clearly"visible"in"a"time"lapse"photograph"of"the"night"sky"• Foucault’s"pendulum"(1851)"proved"Earth’s"rotation"Distance"from"Earth"We"must"consider"huge"expanses"of"space"and"time"• The"speed"of"light"is"186,000"miles/s"(300,000"km/s)"• The"moon"is"1.3"light"seconds"(;237,00"miles)"away"• The"sun"is"8.3"light"minutes"(;93"million"miles)"away"• A"light"year"measures"a"distance"of"5.87"trillion"miles"• Alpha"Centauri,"the"closest"star"is"4.3"light"years"away"• The"visible"universe"is">13"billion"light"years"away"Modern"view"of"the"Universe"• Current"concepts"differ"wildly"from"100"years"ago"• Earth"is"one"of"eight"planets"in"the"solar"system"• The"solar"system"is"on"an"arm"of"the"milky"way"galaxy"• Our"Sun"is"one"of"300"billion"stars"in"this"galaxy"The"Doppler"effect"• Waves"compress"or"relax"with"relative"motion""• Applies"to"waves"of"both"sound"and"light""• The"stopped"train"sounds"the"same"to"Anna"and"Bill"• Anna"hears"a"higher"pitch"from"compressed"sound"waves"• Bill"hears"a"lower"pitch"from"expanded"sound"waves"• As"the"train"passed"Anna,"the"pitch"would"drop"(higher"to"lower)"• This"is"commonly"heard"as"cars"whiz"on"a"road"Light"waves"behave"like"sound"waves"Visible"light"is"electromagnetic"radiation"• Visible"wavelengths"range"from"400"to"700"nanometers"• 400"nm"–"blue=higher"frequency"• 700"nm"–"red="lower"frequency"A"moving"star"displays"Doppler"shifted"light"Light"from"an"approaching"star"is"compressed"• This"causes"a"shift"to"higher"frequencies,"so"that…"• Stars"moving"toward"Earth"are"shifted"toward"blue"Light"from"a"receding"star"is"expanded"• This"causes"a"shift"to"lower"frequencies,"so"that…"• Stars"moving"away"from"Earth"are"shifted"toward"red"The"Expanding"Universe""• Light"from"distant"galaxies"appeared"“red"shifted”"• In"1929,"Hubble"recognized"this"as"a"Doppler"shift"• He"concluded"that"galaxies"were"moving"away"rapidly"• No"galaxies"were"found"to"be"moving"toward"Earth"• This"led"to"the"development"of"the"expanding"Universe"Theory,"analogous"to"expanding"bread""Origin"of"the"Universe"The"Big"Bang"Theory"• When"did"the"expanding"Universe"begin?"• The"best"answer"so"far?"The"big"bang"• All"of"the"mass"and"energy"in"the"Universe"was"packed"into"a"single"small"point"• It"exploded"13.7"Ga"and"has"been"expanding"eve"since"• The"1st"atoms"(hydrogen"and"helium)"of"the"universe"developed"soon"after"the"big"bang."These"atoms"formed"vast"gas"clouds,"called"nebulae""Evidence:"Expansion"of"the"Universe"Hubble’s"Law"• Edwin"Hubble"discovered"that"distant"galaxies"are"uniformly"red"shifted,"rather"than"blue"shiftedgalaxies"are"moving"AWAY"from"us."Other"evidence"for"the"Big"Bang"Universe"Composition"• Started"out~100%"Hydrogen"and"Helium""• Nucleosynthesis"occurred"only"during"earliest"stages"of"the"B ig" Bang"• Explains"present""composition""• ~90%"H"• ~10%"He"• <<1%"heavier"elements"After"the"Big"Bang"With"expansion"and"cooling,"atoms"began"to"bond"• Hydrogen"formed"H2"molecules;"the"fuel"of"stars"• Atoms"and"molecules"coalesced"into"gaseous"nebulae"Gravity"caused"collapse"of"gaseous"nebulae"Collapse"resulted"in"increases"in…"• Temperature"• Density"• Rate"of"rotation"After"the"Big"Bang"• Condense"nebulae"formed"flattened"accretion"discs"• Heat"and"mass"from"collapse"ignited"nuclear"fusion"• These"1st"generation"stars"consumed"H2"fuel"rapidly"• As"the"stars"became"H2"starved,"they"initiated…"• Collapse"and"heating""• Heavy"element"production"• Catastrophic"explosion"(supernova)"Nucleosynthesis"• Stars"are"truly"element"factories"• Big"Bang"nucleosynthesis"formed"lighter"elements"• Heavier"elements"are"from"stellar"nucleosynthesis"• Elements"with"atomic"#s">"26"form"during"supernovae"The"mass"of"a"star"governs"its"element"production"Smaller"mass"stars"(like"the"Sun)"• Burn"slowly"• Live"loner"(10"Ga)"•
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