ASTRO190 HOMEWORK #1, DUE TUESDAY 17 JANUARY.
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1.Whatarethenamesandsinglemostenduringaccomplishmentsoffiveastronomers
orphilosopherspriorto1750whoarementionedinthePrologue?Selectatleastone
fromtheancientGreek-Romanera(before500CE),theyearsfrom1450-1550,from
1550-1650,andfrom1650-1750.Pleasekeepyouranswersbrief.
2.Otherthanage,whatarethreeintrinsicpropertiesofpeople?An"intrinsicproperty"
isonelikeyouragethateveryoneeverywhereandeverywhenintheUniversewould
measureforyou.Careful:"weight"isnotintrinsic.
3.Let’sdevelopsomesenseofcosmicsizes.Gotothewebsite
https://www.youtube.com/watch?v=uaGEjrADGPA
orbetterstill,ifyourbrowsersupportsFLASH(unlikerecentversionsofSafari),goto
http://htwins.net/scale2/
Constructatableoftendiverseastronomicalobjectsarrangedbytheirsizesstartingat
10^0meters(1meter)tothelargestobjectsoftheUniverse(otherthantheUniverse
itself).BesuretoincludetheMilkyWay,the“LocalGroup”ofneighboringgalaxies,and
thelargestobjectscalledsuperclusters.
Yoursizesshouldbeexpressedintwoways:(1)meterswithscientificnotationand
twosignificantdigits(e.g.6.4x10^39)and(2)somesortofsensibleastronomicalunit;
forexample,thedistancethatlighttravelsinaspecifiedtime(calledalight-minute,
light-hour,light-year,kilo(=thousandlightyears),ormega=millionlightyears).Use
scientificnotationfornumbersthatexceedamillionoraresmallerthan0.001.YOUR
ANSWERSSHOULDBEACCURATETOONLYONEORTWOSIGNIFICANTDIGITS!
Forexample,theapproximateradiusofsolarsystemis140billionkm~4lighthours,
andthatoftheMilkyWayisroughly1x1018km~100kilol.y.(~and≈meanapprox.)
4.Themostdistantobjecteverdetectedwasfoundaboutayearagobyverydeep
HubbleSpaceTelescopeobservations.Theobjectseeminglyliesatadistancefromthe
Earthofaround13.4billionlightyears.SeethepressreleaseandHubbleimageat
http://hubblesite.org/news_release/news/2016-07
a.Whymighttheauthorsreasonablyandresponsiblyclaimthattheobjectisadistant
galaxywhentheobjectitselfisbarelydetectedandnodetailsofitsstructurearevisible
initsimage?
b.AbouthowoldwastheUniversewhenthelightthatweseenowwasemittedfrom
theobject?
c.Whatwasobject'sdistancefromuswhenthelightthatweseewasemitted?(your
answershouldbeinbillionsoflightyears)?
d.Howcanwedeterminewhatthisdistantobjectlookslikeatthepresenttime?
5.ThefigureaboveisaschematicdepictionofourUniversetoadistanceof13.8billion
lightyears.Note:WebelievethattheUniverseis13.8billionyearsold=13.8Giga-y.
a.Whydowesaythattheradiusoftheknowableuniverseis13.8billionlightyears?
b.IsthepictureuniversaloristheEarththeonlyplacewherethissketchapplies?
c.Wherearetheyoungestandoldestobjectsmostlikelytobefound?(anobject’sage
ismeasuredbycosmictimesinceitsformation.)
d.(Tricky!)Whycan'ttwoobserverslocatedonoppositesidesofthecircleseeone
anothernow?Explain.
e.Arguethattheradiusoftheknowableuniverseisgrowingattherateof1lightyear
peryear.
Stymied?MyofficeisC318PABandthephoneis543-7683.Don’tuseemail.