详解rmonthi e中秋節文稿

Chapter8:Chapter8:Lunarphases,and1MisconceptionsMisconceptionsabouttheQuestion:RightorTheMoonisonlyvisibleatTheMoonislargerneartotheTheMoonisthebiggestonthe15thofthe8thlunarmonth(i.e.中秋節).WealwaysseethesamesideoftheTheMoondoesnotTheMoondoesnotproducelight.ItislitbyThereisadarksideofthe28.1TheMoon’s••TheMoon’sorbitisalmost8.1TheMoon’s••TheMoon’sorbitisalmostperiod(恆星周期theonce=27.3Theorbitinclinesbyonly5totheEarth’sMoonalwaysappearsneartheecliptic(黃道•4•self-sameas•self-sameasthesidereal•WealwaysseethesamehalfoftheMoonfromthe5668.2Phase8.2Phasecycle(月相之循環7上弦凸漸滿蛾眉上弦凸漸滿蛾眉滿Newmoon新漸暗蛾眉殘8下弦AsimpleAsimplewaytodeterminethetimeof9siderealperiod(siderealperiod(恆星周期):27.3synodicperiod朔望周期29.58.3Tides8.3Tides(潮汐ConsidertheEarth-Moonsystem.ConsidertheEarth-Moonsystem.TheEarth(togetherwithseawater)isalsofallingfreelyunderthegravityoftheMoon(butitneverhitstheMoon).ThesideoftheEarthclosesttotheMoonfeelsastrongerforcethanthecentre,andthecentrefeelsastrongerforcethantheopposite•••relativetothe•relativetothecentreoftheEarth,theinforcepullwaterintobulgesonbothsidesoftheEarthalongtheEarth-Moonline•Twohigh•AlthoughtheMoon’sgravitationalforceonusissmall(~0.0003%thatoftheEarth’s),thetidescannotbeneglected.Thereare•AlthoughtheMoon’sgravitationalforceonusissmall(~0.0003%thatoftheEarth’s),thetidescannotbeneglected.Therearesimilareffectsfromthebutonlyhalfthemagnitude,becausetheSunismuchfartherawayfromtheEarth••SomeexamplesSomeexamplesofToloHighLowBayofImage:BayofImage:Image:WikimediaTidesareaffectedbygeography.Themaximumtidaldifferencedependsonthelocation.MontSaint-MontSaint-~15mbetweenhighandlow(明報(明報新聞圖片Springtides(朔Springtides(朔望潮Theword“spring”doesnotrefertotheseason!Neaptides(弦潮Note:highandlowtidesrefertothelevelofwatercomparedtoothertimeinthesameday.Springandneaptidesrefertothetidalshiftcomparedtoothertimeinthemonth.•Thereisfrictionbetweenwaterbulgessea••frictionalforceslowsdown•Thereisfrictionbetweenwaterbulgessea••frictionalforceslowsdowntherotationofself-the0.001secondper•millionyearsagotheEarth’sdaywas22TheEarth’sgravitationalforceontheMoonalsohastidaleffectstoelongatetheMoon••let’sassumethattheMoonusedtorotatetheMoontheMoonisthereisfrictioninsidetheEnergy•increaseduntil•increaseduntilitisalmostthesameastheMoon’sorbitalperiodtidalcoupling(潮汐耦合):thealwaysshowsthesamefacetowardsTheMoonTheMoonissometimesbiggerontheImage:WikimediaSuper••Thetidal••ThetidalbulgesattracttheTheMoonisaccelerated,itsdistancetotheEarthincreasesslowly(~3cm/year).8.4Eclipses(月食與日食On8.4Eclipses(月食與日食OnthecelestialspheretheMoon’sorbitandtheeclipseintersectattwopointscallednodes(交點).Foreverymonth,theMooncrosseseachnodeonce.WhenboththeSunandtheMoonareclosetothenodes,theSun,theEarthandMoonalignalmostonastraightline•••AneclipseThesenodesarejusttheintersectionsoftheMoon’sorbitThesenodesarejusttheintersectionsoftheMoon’sorbitandtheplaneoftheEarth’sorbit.Whenaneclipseoccurs,thenodallinepointsatornearlyattheLunar••Lunar••TheMoonenterstheEarth’sshadowTheEarth’sshadowhastwoparts:umbra(本影):NolightfromtheSuncanthisalmosttotalpenumbra(半影partialSunlightscatteredSunlightscatteredfromEarth’satmospheregivesthetotallyeclipsedMoonitsreddishcolor.TotallunarTheMoonenterstheumbracompletely;onlysunlightscatteredTotallunarTheMoonenterstheumbracompletely;onlysunlightscatteredbytheEarth’satmospherecanTheMoonappearsredanddimbecause•••Partialeclipse(偏食•Partialeclipse(偏食umbraTheMoononlyenters•TheMoonPenumbraeclipse(半影食enterstheSolareclipse日食TheMoon’sshadowfallsonSolareclipse日食TheMoon’sshadowfallsontheTheMoon’sumbralshadowisatmostabout270km••diameteroftheEarth~13,000Peopleintheumbralshadowcanseeatotalsolar(日全食)atthesameAstheEarthrotates,theshadowsweepsapathoftotaleclipseontheEarthTotaleclipseonlylastsforafewminutesateachlocationontheEarth•••Total•ObserversTotal•ObserversinthepenumbraoftheMooncanonlyapartialsolareclipse(日偏食ShadowofShadowofthe(Image:Mir;(takenfromtheMirspacestation,11AugAnnulareclipse(Annulareclipse(日環食):TheMoonistoofartheEarthtocovertheSunAnnularAnnularAnnularsolareclipseinHongKong,AnnularsolareclipseinHongKong,backin2012Image:Saroscycle沙羅周期Saroscycle沙羅周期BecauseoftheprecessionoftheMoon’sorbit,theSun,theandMoondonotreturntothesamerelativepositionsafter1Theyreturntothesamerelativepositionevery18years11.3••Thisperiod••ThisperiodiscalledtheSarosrepetitio