PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27EclipsesLunar EclipsesSlide 30Slide 31Slide 32Slide 33Slide 34What explains the color?Slide 36Solar EclipsesSlide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48MOON & ECLIPSESDrawn to scalescale:EarthMoonMoon’s orbit – viewed fromabove Earth’s north pole Orbit period = 27.3 days(Sidereal Period)Far sideNear sideNearSideFar Side•Diurnal (Daily) Motion: East to West, relative to horizon; rises & sets•Monthly Motion: Eastward relative to stars; due to orbit of moon about Earth MOTION OF THE MOON (Viewed from Earth)Orbit, viewed edge-on:Earth’s orbit planeMoon’s orbit plane5o- Orbits tipped  Orbit planes intersect along“Line of Nodes” *p. 41Viewed from Earth, moon moves ~ 13o/day E S W9 pm9 pm9 pm13o13oDoes the moon rotate?eh?The Lunar Phase Cycle E Wp. 39WestHorizontoward sunWaxing CrescentSouthHorizonFirst QuarterSouthHorizonWaxing GibbousSouthHorizonFullSouthHorizonWaning GibbousSouthHorizonThird (Last) QuarterEastHorizonWaning Crescenttoward sunPhaseMoviePhaseMovieE WThe Full Cycle29.5 days –One‘moonth’p. 39Sunlight Just like Earth!- Phases result from viewing, from Earth, fractions of illuminated half.- Moon is always one-half illuminated.Understanding the Phase CycleSunlightNote: Not to scaleEarthMoone.g., First QuarterView from EarthResult: Moon appears one-half illuminatedPhase VisibilityEclipses•Shadows> Umbra: Inner shadow> Penumbra: Outer shadowp. 41Lunar Eclipses•Moon moves through Earth’s shadow•Require> Full Moon> Moon along nodal lineThe moon was as though drenched with blood.- The Anglo Saxon Chronicles (734 AD)Note: not to scaleThe View from Space* Maximum duration of totality  100 minp. 42The View from EarthDuration: 77 minPartial Eclipse of July 28, 1999Lunar eclipse occurs only when moon at/near nodal line No eclipse!Eclipsep. 41From a vantage point in the plane of Earth’s orbit . . .Earth’s shadow misses moon  no eclipse!5oWhat explains the color?SunlightMoonEarthAtmosphere- Atmosphere bends (refracts) sunlight into umbra- Atmosphere removes (scatters) blue/green part of light.Earth’s shadowEclipse of Jan 20 – 21, 2000“. . . the moon drenched with blood.”Solar Eclipses•Earth intersects moon’s shadow•Require> New Moon> Moon along nodal line•Eclipse can be> Total> Partial> AnnularAnd the moon in haste eclipsed her,and the Sun in anger sworeHe would curl his wick within himand give light to you no more.- Aristophanes, Chorus of Clouds (423 BC)Basic Geometry of Solar EclipseUmbra forms spot (diam ~ 100 mi) on EarthAnother ViewSpot moves generally eastward at ~ 1100 mi/hr, creating “zone of totality”Partial eclipseseen in penumbrap. 43View from Earth:Sun, totally eclipsed.Solar CoronaMaximum duration of totality: ~7.5 minutesSun, partially eclipsedClosestFarthestMoon’s orbit is not a circle . . .Yielding Annular Eclipses:Earth Moon Sun Moon’s umbra does not reach Earth whenmoon too far away.p. 43Ring or Annulus is seenwhen sun eclipsed.FarthestClosestAug 24, 1998•Solar: about twice per year, somewhere on Earth.> At any given location, about once in 360 yrs.•Lunar: about twice per year.How often do eclipses occur?Total Solar Eclipses: 1997 - 2020p.