Outline for Astronomy Lecture: The Moon and Mercury - Prof. Robert Weigel, Study notes of Astronomy

Download Outline for Astronomy Lecture: The Moon and Mercury - Prof. Robert Weigel and more Study notes Astronomy in PDF only on Docsity! 1 Outline for 31 October (Tuesday) • The Moon • Mercury Key Words • anorthosite • capture theory • center of mass • co-creation theory • collisional ejection theory • crater • far side (of the Moon) • fission theory • impact breccia • impact crater • libration • lunar highlands • mare (plural maria) • mare basalt • moonquake • refractory element • regolith • synchronous rotation • terminator • terrae • volatile element Theories How did the moon form? • Getting data to answer this was one of the science objectives for the Apollo program. • What was the (social) driving force for the Apollo program? Theories • Fission – Part of Earth tore away because Earth was rapidly rotating – Where did the chunk come from? – Would expect more similarity in Moon and Earth rocks • Capture – Wandering moon was captured by Earth’s gravity – Computer simulations show that it is highly unlikely • Co-creation – Formed at same time but separately – Iron content mismatch • Collision (collisional ejecta theory) – Mars-sized object collided with Earth – Our current best guess How did the moon form? 2 Question • The terminator on the Moon is a line – A) joining north and south lunar poles, passing through the center of the largest mare, Imbrium, representing 0° of lunar longitude. – B) between the near and far sides of the Moon. – C) between the solar-illuminated and dark hemispheres. – D) along the equator, between northern and southern hemispheres. Question • The terminator on the Moon is a line – A) joining north and south lunar poles, passing through the center of the largest mare, Imbrium, representing 0° of lunar longitude. – B) between the near and far sides of the Moon. – C) between the solar-illuminated and dark hemispheres. – D) along the equator, between northern and southern hemispheres. Question • If you were standing on the Moon with Earth in view, how much time would elapse between two successive "Earthrises"? – A) about 1 synodic month – B) about 1 day – C) about 1 sidereal month – D) infinite time, because the same side of the Moon always faces toward Earth Question • If you were standing on the Moon with Earth in view, how much time would elapse between two successive "Earthrises"? – A) about 1 synodic month – B) about 1 day – C) about 1 sidereal month – D) infinite time, because the same side of the Moon always faces toward Earth Question • Maria are – A) bright streaks radiating away from young, fresh craters. – B) isolated regions of heavily cratered highland terrain. – C) long, sinuous valleys formed by ancient lava rivers. – D) ancient lava floodplains. 5 The Moon’s rotation always keeps the same face toward the Earth due to synchronous rotation Mercury’s orbital period is 88 days Mercury’s rotation period is 58 days A B C D Draw ball and arrow at A, B, C, D Mercury’s orbital period is 88 days Mercury’s rotation period is 58 days A B C D Draw ball and arrow at A, B, C, D Mercury’s orbital period is 88 days Mercury’s rotation period is 58 days A B C D Draw ball and arrow at A, B, C, D 88/4 = 22 days to get to A 22/58 = 0.375 Mercury’s orbital period is 88 days Mercury’s rotation period is 58.6 days A B C D Draw ball and arrow at A, B, C, D 88/4 = 22 days to get to A 22/58 = 0.375 0.375 of a full turn First rotate around Mercury’s axis. Then move into position in orbit. Mercury’s orbital period is 88 days Mercury’s rotation period is 58 days A B C D Draw ball and arrow at A, B, C, D 88/4 = 22 days to get to A 22/58 = 0.375 6 Mercury’s orbital period is 88 days Mercury’s rotation period is 58 days A B C D 88/4 = 22 days to get to A 0.375 of a turn 0.75 of a full turn 1.125 turns 1.5 turns Observations • Observing Mercury – What are best conditions to observe • Unusual spin – How suspected to be unusual – Why unusual – How verified – How to make a guess that will make you famous • Craters – How similar to the moon – How different • Unexpected magnetic field – Why unexpected – How measured • Heavily cratered surface • Less dense cratering than moon • Gently rolling plains • Scarps • No evidence of tectonics Note how much more densely the craters occur on the moon’s surface. Scarps are cliffs This one is more than a km high They probably formed as the planet cooled and shrank 7 • The Caloris Basin is evidence of a large impact The seismic waves from the impact that caused the Caloris Basin caused this deformation on the opposite side of Mercury Observations • Observing Mercury – What are best conditions to observe • Unusual spin – How suspected to be unusual – Why unusual – How verified – How to make a guess that will make you famous • Craters – How similar to the moon – How different • Unexpected magnetic field – Why unexpected – How measured The magnetosphere blocks the solar wind from reaching the surface of the planet Questions • 6.It is relatively difficult to observe details on the surface of Mercury from Earth because – A) detail is obscured by bright glows from hot regions of molten surface heated by the intense sunlight. – B) its orbit always keeps it on the opposite side of the Sun from Earth. – C) it is a small object that always appears close to the Sun in the sky. – D) its surface is always completely covered in clouds.