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This 6 page Class Notes was uploaded by Ashley Childers on Friday October 16, 2015. The Class Notes belongs to AST 111 at University of Southern Mississippi taught by Christopher Sirola in Summer 2015. Since its upload, it has received 15 views. For similar materials see General Astronomy in Physics 2 at University of Southern Mississippi.
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Date Created: 10/16/15
a 9 I h A l 7 l Tm I l e ll IlIIIItiEEE quot a V r I 7 L l1 J The moon has no active geology so it is dominated by impact features 0 Terra mare crater rays 0 No weather atmosphere or liquid water extreme temperatures during the day and night no shielding from the radiation from the sun quotTerraequot or the lunar highlands are regions saturated by individual impact craters o The lunar highlands look relatively bright from a distance due to wide scattering of light 0 Most craters are name after famous astronomy gures Copernicus Crater Aristarchus Crater Dark Material is quotimpact meltquot and light material is rock that was excavated by the impact 0 Individual rock thrown about are as large as 100m across o Craters are generally shaped like bowls wide across and shallow Notice that the walls of craters are not smooth the walls are slump back down collapsed back down The impacts that form craters also tend to form crater peaks 0 The Tycho crater the peak is about 15km 10ml and 2km 1 mi high The impact that formed it occurred about 100 mya million years ago JAXASELENE o Occasionally we see craters with quotraysquot emitting from them Such features are relatively young lmpacts can be energetic enough to melt some of the rock into tin glass beads This picture is on the 14 mm scale it is a bead brought back to earth by the Apollo astronauts it also has impact craters Making craters 0 An object such as a small asteroid falls toward the surface It does not have to fall straight down 0 Due to gravity the object will be falling at or above the escape speed of the target object this would be about 17 kms 4000mph for the moon 0 At these speed the impacting object virtually disintegrates in a violent explosion Some of the rock object and surface both may be melted If the asteroid is large enough it can resemble a nuclear blast minus the radiation 0 The mushroom effect only happens if there is an atmosphere because it pushes back on the debris The explosion sends shockwaves through the ground and debris ejecta outward l The width of a crater is typically several tens of times larger than the object asteroid or comet that created it o Crater rays form when thin bright dust formerly underground is sprayed across the landscape 9quot After the shockwave passes by the ground tries to quotii rebound to its original shape The ground doesn t fully recover but the rebounding waves focus at the epicenter of the original impact The rebounding shockwave can make a crater peak in the very center 0 The crater walls slump back o Impacts along with basic physics principles like gravity help determine the appearance of the solar system objects The near side of the moon right by contrast shows smooth dark patches as well as created highlands Nlear left and liar rig ht sides of the Moon Taken by tile nlar Reconnaissance Orbiter Mare dark areas on the moon the seas of the moon 0 Fewer craters that the highlands 0 Most quotlunar seasquot are simply impact basins Very large impact crater 0 Impact basins form due to the collision of extremely large objects with the moon 0 Molten lava covers regions hundreds or thousands of miles across 0 Most of the maria formed several billion years ago Origins of the moon o It seems the origin of the moon itself is due to a very very large impact 0 Moen Ferimietieh lmpaeter o The moon s overall density is 334 gcc much less than Earth s 554 gcc Moon has a much smaller metallic core 0 The plane of the Moon s orbit is close to the plane of the Earth s orbit We would expect the moon to orbit the Earth s equator if it formed with us 0 Analysis of lunar rocks returned by astronauts show they have the same isotopes unique version varied composition of oxygen as does the Earth Composition is similar to volcanic rock not same amount of oxygen We would expect the Moon s composition to be either all different or all the same 0 Finally the moon is very large for its planet 14th the Earth s diameter and greater that 1 of Earth s mass Except for Pluto no other planet has a moon even remotely as large compared to its planet as we do 0 The leading theory is that an object about 12 the size of the Earth hit it as a glancing angle 0 The other object would have been a small planet orbiting the sun on its own until it crossed our path o 0 Most of the debris would have gone back into interplanetary space or fallen on the Earth 0 Both objects would have been molten Much of the incoming object would have sunk into the Earth For a while the earth would have sported a more spectacular set of rings than Saturn s Eventually most of the ring material would coalesce in one body the moon The nascent moon would have remained volcanic for nearly its rst billion years Detailed gravity eld measurements for the Kopernick satellite in 2014 show evidence of ancient lava ow Origins Explained O O O 0 Why the moon orbital plane is like that of a planets Came from a planet Why the moons density is so low Earth stole materials in the crash Why some isotopes are the same Lighter material was shared What the moon is large compared to Earth The original object was itself very large One more thing 0 O O The Earth s obliquity is very stable only changing a few degrees Compared to the Mars tilt Earth is very stable This is because of the Moon