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Cosmology(ancientview)

Isthebranchofastronomyconcernedwiththestudyoftheoriginsandul6matefateoftheUniverse

Babylonians(~1400BCE): keptcarefulrecordsofmo6onsofplanetsandthemoon

BelievedtheEarthwasthecentreoftheUniverse

Indians(~1000BCE): cyclicaluniverse(birth-destruc6on)

Greeks(~700BCE): startedtodeveloptheoriesbasedonobserva6ons

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Cosmology(ancientview)

ThalesofMiletus(3454BCE) developedasimplemodelwiththetheEarthasaflatdisksurroundedbywater

Anaxagoras(500-428BCE) proposedtheworldwascylindricallyshapedandhumanslivedontheflat-toppedsurface thecylinderrotatesinspacethatiswhythestarsmove themoonreflectsthelightfromthesun eclipsesareduetotheEarthsshadowontheMoon

Aristotle(384-322BCE) geocentricmodel

Aristarchus(310-230BCE) wasthefirsttosuggesttheEarthorbitstheSun madeanes6mateofthedistancebetweentheMoonandtheSun

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Copernicanmodel

NicolausCopernicus(1473-1543) proposedthattheEarthwasnotthecentreoftheUniverse planetsorbittheSunincircles

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KeplerandGalileo

JohannesKepler(1571130) proposedthattheplanetsmoveinellipses derived3lawsofplanetarymo6onthatfitthedataperfectly suggestedtheuniversewasinfinitewithinfinitenumbersofstars starsareextremelyhotandbright

Galileo(152-142) foundevidenceofheliocentricmo6on discoveredfourofthemoonsofJupiter discoveredSunspots

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ModernCosmology

TheUniverseishomogeneousandisotropic Sunisapproximately2,000l.y.fromgalac6ccentre MilkyWaygalaxyhasbetween200-400billionstars

100,000lightyears

ThediameteroftheMilkyWaygalaxyisbetween

100,000-120,000l.y.

Thecentreofthegalaxyhostsasupermassive

blackhole(SagitarriusA*)

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NebulaeandGalaxies

HarlowShapley(1885-1972) Arrivedatthefirstes6mateofthesizeoftheMilkywaygalaxyandtheposi6onoftheSuninit

VestoSlipher(1875-199) usedspectroscopytodeterminetherota6onofspiralnebulae no6cedthatthelightcomingfromthoseobjectswasredshied

AlbertEinstein(1879-1955) publishesGeneralTheoryofRela6vityin191 assumesinfiniteandsta6cuniverse

WillemdeSier(1872-1934) mathema6callyprovestheuniverseisexpanding

AlexandrFriedmann(1888-1925)yes,itis

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NebulaeandGalaxies

ArethesespiralnebulaejustgascloudsinsidetheMilkywaygalaxyoraretheyothergalaxiesmuchfurtheraway?

EdwinHubble(1889-1953) observedmanyspiralnebulaeandworkedouttheirdistancesconfirmingtheviewthattheywereoutsidetheMilkyWaygalaxy

Ellip6cals(E)

Spirals(S)

BarredSpirals(SB)

Len6cular(S0)

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NebulaeandGalaxies

ArethesespiralnebulaejustgascloudsinsidetheMilkywaygalaxyoraretheyothergalaxiesmuchfurtheraway?

EdwinHubble(1889-1953) observedmanyspiralnebulaeandworkedouttheirdistancesconfirmingtheviewthattheywereoutsidetheMilkyWaygalaxy

galaxiesaremovingawayfromus thefurthertheyare,thefastertheyaremovingaway HubblesLaw:v = H

0d

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NebulaeandGalaxies

1931data1934data

H0=725kms-1Mpc-1

Bestcurrentes6mate

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DynamicsoftheUniverse

Dependingonhowmuchmaerthereisintheuniverse,theexpansionwill:

a)eventuallystop(flatuniverse) b)eventuallyreverse(closeduniverse) c)con6nueforever(openuniverse)

Open

Flat

Closed

>1

=1

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DynamicsoftheUniverse

Iftwogalaxiesaremovingawayfromeachotherwitha

constantspeedv,thentheirdistancewith6mechangesas

d=vt

v=H0d

H0=725km/s/Mpc

1Mpc=3.081022m

1second=3.1910-8years

Es6matedageoftheuniverse

t=1/H0

t=1

721033.08610

223.16910

8=13.610

9 years

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TheBigBang

NowSunforms

Firststarsandgalaxies

Recombina6onepoch

Radia6ondomina6on

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Justanothertheory?

Evidence ExpansionoftheUniverse Cosmicmicrowavebackgroundradia6on Chemicalelementabundanceintheuniverse

A.PenziasandR.Wilson

R.Dicke

COBEspacecra

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ToDo

Readsec6on21fromthebook[AstronomyandCosmology] HomeworkAssignmentwk11:(seeblog) Handitinnolaterthan4:00pmWednesday3rdApr-LATEWORKWILLNOTBEACCEPTED

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