Water on the MoonCourse AnnouncementsAssignmentsQuiz 4 ResultsTidal LockingTidal LockingTidal LockingTidal LockingThe Synchronous Orbit of the MoonLunar LibrationThe Synchronous Orbit of the MoonThe Synchronous Orbit of the MoonThe Synchronous Orbit of the MoonThe Synchronous Orbit of the MoonChapter 8The Moon Data Sheet ISurface Features – The MoonSurface Features – The MoonNear Side – Far Side DichotomySurface Features – CratersTypes of CratersImpact Crater related phenomenaCrater Counting and Relative DatingCrater Counting and Absolute DatingCrater Counting and Absolute DatingLunar RegolithLunar RegolithLunar Regolith – Eroding featuresLunar IceLunar IceLunar IceLunar IceLunar VolcanismLunar VolcanismInteriors - MoonInteriors - MoonWater on the MoonCredit: NASA/LROSouthern Polar Region Blue indicates neutron detections associated with H20Course Announcements•Thanksgiving Week planningNo classes Wednesday, 23 Nov.Upcoming Schedule•Quiz 4: Graded and available for pick-up•Exam 2: Friday, 28 October–Chapters 5, 6, 7, Dr. Lindsay’s Custom Material, parts of Ch. 8. [wherever I get to on Wed.]–Study session tomorrow: Thursday at 6pm in Room 304 of Nielsen Physics and Astronomy–MA study guide, “Must Knows”, and Chapter slides all now available–Will not include Formation of the MoonAssignmentsReading Assignments•No new readingParallel Lectures•CC Astronomy – Episode 12: The Moon[Watch before exam Friday, 28 Oct.]Mastering Astronomy•Chapter 8 Homework available.[Due Wed., 2 Nov. at 11:59 PM]Quiz 4 ResultsNicely done•Be sure to review “how to tell if atmosphere” and “how to tell if we expect a magnetic field”–Critical rotation period I said is 25 days, not 25 hoursRawMean 7.5Median 8.0St. Deviation 1.8Tidal LockingThe Moon is retreating and Earth’s rotation is slowing (days are getting longer)Force of gravity(Moon acting on Earth’s Tidal Bulge)Pulls bulge back (against rotation)Moon pulling on Earth’s Tides is slowing down Earth’s RotationTidal LockingThe Moon is retreating and Earth’s rotation is slowing (days are getting longer)Force of gravity(Tidal Bulge acting on Moon)[equal, but opposite)Pulls moon forwardEarth’s tidal bulge is pulling Moon forward making it move away from EarthTidal Locking•The Tidal Bulge gets dragged along by Earth’s rotation pulling it off center with the Moon.•The Moon then pulls backward on the Tidal Bulge causing a drag on Earth’s rotation•Earth’s spin rate (23h56m days) is slowing down… THE DAYS ARE GETTING LONGER–Evidenced by diurnal fossil evidence in coral–620 million years ago: 21.9 hour days… 400 days per year–+2.3 milliseconds per centuryTidal Torques slowing Earth’s RotationTidal Locking•Angular momentum is conserved and loss due to Earth’s slowing spin goes into orbital motion of Moon.–Moon slowly retreating from Earth at a rate of 4 cm per year.–Will continue to do so until Earth’s rotation slows to match the orbital period of the Moon, i.e., the Earth rotates at exactly the same rate as the Moon orbits.•At this point, Earth will take 47 of our present days to rotate, and the Moon will be 47% further away than it is now.•Will take many billions of years… we will have bigger problems by thenMoon is retreatingThe Synchronous Orbit of the Moon•The Moon always shows (almost) the same face. Why is that?•The face that we see from Earth is the Lunar near side; The face we never see from Earth is the Lunar far side.•Before the 1960s lunar exploration period, we had never observed the Lunar far side•We actually see more than 50% of the Moon due to it’s elliptical orbit causing what is known as Lunar libration (or rocking back and forth oscillation)There is no dark side of the Moon… only a near side and far sideLunar LibrationCan see 59% of the surface of the Moon from Earth due to the Moon’s slightly elliptical orbitThe Synchronous Orbit of the Moon•The Moon always shows (almost) the same face. Why is that?There is no dark side of the Moon… only a near side and far sideLunar Near Side Lunar Far SideThe Synchronous Orbit of the Moon•The Moon always shows (almost) the same face. Why is that?Answer: The Moon’s rotational period (spin on its axis; 27.3 days) is exactly equal to its orbital period (motion around the Earth; 27.3 days)Moon’s Rotational Period = Moon’s Orbital PeriodHere, we say that the the spin is synchronized to the revolution. This is an example of what is known as a synchronous orbit. - 2 weeks of daylight; 2 weeks of nightThere is no dark side of the Moon… only a near side and far sideThe Synchronous Orbit of the MoonRotational period = orbital period•Reason for this is that the Earth causes tides on the Moon.–i.e., creates a tidal bulge on the Moon–How it works is the same tidal locking concept that is slowing Earth’s rotation down.–Moon has less mass, so the slowing down process has reached it’s completionThe Synchronous Orbit of the MoonRotational period = orbital period•This process of synchronizing orbital and rotational periods is called tidal locking–We say the Moon is tidally locked to the Earth•Most moons in solar system are tidally locked to their planetsCHAPTER 8The Moon and MercuryMercury Composite Image from MESSENGERThe Moon from a 6 inch Newtonian RefectorThe Moon Data Sheet I•Distance from Earth: 384,000 km•Radius: 1,738 km (0.27 Earth radii)•Mass: 7.3 x 1022 kg (~1/8 Earth Masses)•Average Density: 3,300 kg/m3•Surface Gravity: 1.62 m/s2 (~1/6 Earth gravity)•Orbital Period: 27.3 days ; Rotational Period 27.3 days•Mean Temperatures: Equatorial: 220 K; Polar: 130 K–Large variation between daytime and nighttime temperatures–Extremely cold polar regions•Atmosphere: No•Global Magnetic Field: NoSurface Features – The MoonThe two dominate surface features are: 1. The lunar maria (singular: mare, which is the Latin for Sea)–Young compared to the highlands with overall fewer craters (smooth)–Darker in color due to higher iron content in rock–Representative of lunar mantle material2. The cratered highlands–Elevated by several km above maria–Older surface with more craters–MountainousDominated by lunar Maria and Cratered HighlandsSurface Features – The MoonDominated by lunar Maria and Cratered HighlandsMare (pl., Maria)Younger, darker, smooth parts of the Moon’s surfaceCratered HighlandsOlder, lighter, rough and mountainous parts of the Moon’s
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