ImportanceofAstronomy KnowingtheHeavens
1. a. Astronomyhadabigroleinancienttimes i. Thingswerebuiltbasedonastronomicaleventssuchaseclipsesorotherthings ii. Astronomywasimportantbecauseinitially(25thousandyearsago)thestarswerethemeans oftellingtime b. Studyingthestars i. Thehumaneyecantellthedifferencebetweenthecolorsofstars ii. Constellations 1. Theywerebuiltbecausegroupsofstarsformedapatternandweregivenaname 2. Today,theskyiscutinto88divisionsorconstellations.Eachstarineachdivisionis partofthatconstellationwhetherornotyoucanseethestars. 3. Youcanonlyseeabout6,000starswiththenakedeye,andyoucanreallyonlysee about3,000,whichallfitintosomeconstellation. 4. Mythologygoesalongwiththeconstellations,andwewentmorewithNative American,GreekandRomantraditionalmythology. c. Earth i. OnlyhalfoftheEarthisilluminatedatonetime.Sincetheearthisconstantlymoving,the skyandstarsappeartomove. 1. Inreality,theearthismoving,butsinceweseemtostayatthesameposition,wesee thattheyriseintheEastandsetintheWest. 2. Starsareupforabout12hours,butthatdoesntmeanyoucanseeit. a. Beingvisibleisnotthesamethingasitbeingup! ii. Earthrotatesinonewayandweconstantlyorbit, 1. Overtime(months),theearthmovesinorbitanddifferentconstellationsareinthe sky. iii. Earthsorbitisprettybig,sowehavetwomotionstoconsider. 1. Starswillrise4minutesearliereveryday(2hourseachmonth)applythistothe seasonalstarsexercise d. Cardinaldirections i. IfyouknowNorth,youknowthewest 1. LookfortheBigDipper,andtheladlepointstoaregionwithaverybrightstar,which isPolaris(NorthStar) a. ThisonlyworksinNorthernHemisphere 2. CelestialSphere a. Pretendearthisinthecenterofasphere i. Ifthestarsareputontheinsideofthesphere,andthecelestialpolesandequatoraretacked on,theneverythingwillsimplyrotatearoundtheearth b. Tomakethingsmorecomplicated,weareonacontinentnotonapoleortheequator i. Wehavethecelestialpolesandequatorsaswellastheplanets.Zenithisalwaysaboveyour head.
c. BecausetheEarthistiltedandweareatabout35degreesabovethenorthernhorizon,weseethings alittlecrocked i. Weareat35degreeslatitudeontheearthandthenorthstaris35degreesabovethehorizon. d. Theextremesforobservation i. Ifyouaresittingatthenorthpole,starsdonotriseorset,butjustgoaroundinacircle ii. Ifyouaresittingattheequator,thestarsgostraightup iii. Atthemiddlenorthernlatitudes,starsriseintheeastandsetinthewest.However,ourstars havetodipsouth. e. Coordinatesystem i. ItisanalogoustotheEarthscoordinatesystem,buttheyaretwodifferentthings 1. RArightascension(onequator)intermsofhours,minutesandseconds 2. Declinationtellsyouhowfarnorthorsouthyouarefromtheequator 3. Vernalequinoxisaveryimportantpositioninsettingclocks f. Nowdothepositionandmotionactivities 3. TimeKeeping a. Theearthisonatilt,andthereferenceofthetiltistheorbit. i. Theearthisatanangleof23.5degrees.Becauseofthistilt,wegetseasons. ii. Reasonsfortheseasons 1. Concentrationoflight a. Ifthelightismoreconcentrated,thentheearthheatsupfaster.Thinkofa magnifyingglasshelduptoalightsource. b. Themoreconcentratedthephotonsare,thehotteritgets. i. Whenthelightismoreconcentrated,itissummer. ii. Whenthesunisasadrasticangle,thesamenumberofphotonsare spreadout,whichcreateswinter. 2. Exposuretotheheatsourceaffectsthelengthoftheday a. Insummer,theexposurelengthismuchlonger.Thisgivesusmoreexposure tosunlightandlongerdays. b. Inwinter,theexposureislessconcentratedandgivesusshorterdays. 3. Thetiltoftheearthreallycreatestheseasons iii. Ifyougoouteverydayandputthesunonthecelestialsphere,therewillbeapathknownas theecliptic 1. Theeclipticisthepathofthesunonthecelestialsphere Fromtheequator,theeclipticistilted23.5degrees a. 2. Whenthesunissettingattheequator,yougetanequinox a. VernalequinoxisMarch21,whichisequaldayandnight b. TheAutumnalequinox 3. Whenthesunisatanextreme,thereisasolstice a. Thesummersolsticeat+23.5degreesisthelongestdayoftheyear b. Thewintersolsticeat23.5degreesistheshortestdayoftheyear iv. Fourextremes 1. December21istheshortestday,andthesunisasfarsouthasitgets.Itdoesnotrise dueeastbutrathersoutheast.Itrisesandsets,andisnotupverylong.
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2. March21andSeptember22arethefirstdaysofspringandfall.Thesunisonthe equator,whichgivesusequalamountsofdayandnight. 3. June21iswhenthesunisatitsmostnortherlyposition.Thisisthelongestday becausethesunisintheairforthelongestamountoftime a. InBatonRouge,thesunwillneverbedirectlyoverourheads! b. FromZenith,welook6.5degreessouthtoseethesun v. Timetothink 1. SummeroccursinthenorthernhemisphereoftheearthinJuneandJulybecause a. ThenorthernhemisphereofEarthisclosertotheSunthanthesouthern hemisphereWRONG b. Daysarelongerinthenorthernhemispherethandaysinthesouthern hemisphereCORRECT c. ThesunlightstrikesthenorthernhemisphereoftheEarthatananglecloseto theverticalCORRECT d. Bothcandd Meridian i. Whenthesuncrossesthemeridian,wedefinethatasnoon ii. Whenthesunisintheeast,itisentermeridianAM iii. Ifitisinthewest,itispostmeridianPM Thesunsetstheyear i. Whenthesunrisesonaspecificplaceontheearth,ittakesabout365daystogetback Thesunisapoortimekeeper i. Theearthmovesfasterinorbitinsomeplacesthaninothers. ii. Whentheearthisclosertothesun,itmovesatadifferentratethanwhenthesunisfarthest awayfromthesun Days i. Solarday 1. Timefromnoontonoonmeridiantomeridian 2. Themeansolarratewasusedtodeterminethelengthofaday ii. Siderealday 1. Thisisafullrotationoftheearth,whichis360degrees.Thisislessthanthen24hour daybecausethisisonlya360turn.Astheearthmovesalongitsorbit,eachdayit moves1degree(starsrise4minuteslater,etcetera). iii. TimeZones 1. Thesecomefromevery15thlongitude.Each15thlongitudeisthecenterofthetime zone a. Onaveragetheseare15degreeswide 2. Theclockstartsatnoonwhenthesuncrossesthemeridianonthatlatitudeonvernal equinox iv. DaylightSavingsTime 1. Thishasanagriculturalroot.Thefarmerswantedanextrahourofdaylightsothat theycouldworkmore. v. Weareat92degreeswest,andourtimezoneissetonthe90degreelatitude
f. Calendar i. Theoriginalcalendarhad13months,eachoneonly30days.Thiswasbasedonthemoon cycle. 1. Theancientpeopledescribedeverythingastheysawit a. Theirreferenceswerebasedonthelifecycle.Theybasedeverythingonlife, sotheiroriginalfirstmonthoftheyearwasMarchbecausethe i. Septemberwasthe7thmonth,Octoberwasthe8thmonth,etcetera b. PeoplecomplainedtoCaesarbecauseholidayswerenotthesameeachyear,so theycreatedaleapyearevery4yearsthataddedadaytothelastmonthofthe year,whichwasFebruary29. i. JuliusCaesarcreatedJulyinhisname,thenAugustusnamedAugust. Thesemonthsalsoaddedanadditionaldayandtookthemfrom February. c. Onlyoncenturyyearsdivisibleby400,youaddadayGregorian i. Almost2weeksoftimehadtoberippedout. ii. Ourcalendarnowisbasedonasuncycle 4. EarthsRotation a. ThereisatugofwarontheEarthbetweenthesunandthemoon.Thishascausedthingstoshift. i. In2600years,Polariswillbethenorthstaragain 1. Basically,thereisa2600yearrotationofthenorthstar
1. Atnoon,thesunwillbetotheeast,notdirectlyaboveus! 2. Unitscomeintothis.Starsrise4minuteseveryday,whichisabout1degree. 3. Ifweare2degreeswestof90,andeachdegreeisworth4minutes,ourlocalsolar noonisactuallyat12:08everyday.