Water on the Moon Credit NASA LRO Southern Polar Region Blue indicates neutron detections associated with H20 Course Announcements Thanksgiving Week planning No 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 Moon Assignments Reading Assignments No new reading Parallel 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 Results Nicely done Mean Median St Deviation Raw 7 5 8 0 1 8 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 hours Tidal Locking The Moon is retreating and Earth s rotation is slowing days are getting longer Pulls bulge back against rotation Force of gravity Moon acting on Earth s Tidal Bulge Moon pulling on Earth s Tides is slowing down Earth s Rotation Tidal Locking The Moon is retreating and Earth s rotation is slowing days are getting longer Pulls moon forward Force of gravity Tidal Bulge acting on Moon equal but opposite Earth s tidal bulge is pulling Moon forward making it move away from Earth Tidal Locking Tidal Torques slowing Earth s Rotation 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 century Tidal Locking Moon is retreating 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 then The Synchronous Orbit of the Moon There is no dark side of the Moon only a near side and far side 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 Lunar Libration Can see 59 of the surface of the Moon from Earth due to the Moon s slightly elliptical orbit The Synchronous Orbit of the Moon There is no dark side of the Moon only a near side and far side The Moon always shows almost the same face Why is that Lunar Near Side Lunar Far Side The Synchronous Orbit of the Moon There is no dark side of the Moon only a near side and far side 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 Period Here 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 night The Synchronous Orbit of the Moon Rotational 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 completion The Synchronous Orbit of the Moon Rotational 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 planets CHAPTER 8 Mercury Composite Image from MESSENGER The Moon and Mercury The Moon from a 6 inch Newtonian Refector The 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 No Surface Features The Moon Dominated by lunar Maria and Cratered Highlands The 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 material 2 The cratered highlands Elevated by several km above maria Older surface with more craters Mountainous Surface Features The Moon Dominated by lunar Maria and Cratered Highlands Mare pl Maria Younger darker smooth parts of the Moon s surface Cratered Highlands Older lighter rough and mountainous parts of the Moon s surface Near Side Far Side Dichotomy Near side dominated maria and has cratered highlands Far side has few maria and is dominated by highlands Lunar Near Side Lunar Far Side South Pole Aitken Basin SPA Like two sides of a coin Surface Features Craters Remnants of meteor impacts Impact Craters are bowl shaped depressions with rims created during a meteor impact event Dominate feature on airless bodies such as the Moon and Mercury Come in two main forms simple and complex craters Types of Craters On the Moon Simple Crater Round bowl shape with uplifted rim Small impactor Complex Crater Round fat bottom bowl shape with uplifted rim and central peak Large impactor Impact Crater related phenomena More than just holes Subsurface below impact crater is pulverized cracked and broken up technical geology term brecciated The ejected material is called ejecta Spreads outward in all directions Can form ejecta blankets and ejecta rays Ejecta can be large and cause secondary craters Tycho Crater with ejecta blanket and rays Lighter
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