Lunar Motion and Phases: Understanding the Moon's Orbit and Phases - Prof. Phillip J. Mart, Study notes of Astronomy

Download Lunar Motion and Phases: Understanding the Moon's Orbit and Phases - Prof. Phillip J. Mart and more Study notes Astronomy in PDF only on Docsity! 1-4: Lunar Motion & Phases Image Courtesy of Mike Kozma Earth & Moon Earth Sun 0.5o Angular diameter of the Sun viewed from Earth is likewise 0.5o. Earth Sun 0.5o Angular diameter of the Sun viewed from Earth is likewise 0.5o. Moon is much closer! 390 km 384,000 km 10 1.5 Moon to Dist Sun to Dist 8    Your index finger, held at arm’s length, subtends about 1o - 2o. Lunar Motions Moon’s orbit – viewed from above Earth’s north pole: counterclockwise  Orbit period = 27.3 days (Sidereal Period) Far side Near side Cha Sy tele Rotation Period = 27.3 days Moon’s rotation period = its orbital How it would be IF Moon did not period. It keeps ane side facing the Earth. rotate. Sametimes we would see We never see far side of Moon (shaded), far side of Moon. Moonsync.mov (Moon Rotation Movie) [Exit ‘show’ mode; right click on caption; select ‘package object/activate contents.’] Orbit Orbit, viewed edge-on: Earth’s orbit plane Moon ’s orb it plan e 5o Moon’s orbit plane is tilted slightly relative to Earth’s orbit plane. Another view . . . Plane 5o (Line of Nodes) View From Earth Viewed from Earth, moon moves ~ 13o/day E S W 9 pm9 pm9 pm 13o 13o Because Earth’s orbit & the Moon’s orbit are tilted by 5o, the Moon is never more than 5o from the ecliptic . . . . . . consequently, rising & setting points wander only a little more than Sun’s rising & setting points. Lunar Phase Cycle A Anen ea Gres ae re ' Horizon Bees cieim elie rsa Horizon: . . : : ‘. care Sera esaraken Yi cae . ; Third (Last) Quarter . ee Sera eV korres ae { a an cs ae Aaa _ eC Po . i. 7 One eae 7 - ; a ; a a aa Sunlight Note: Not to scale Earth Moone.g., First Quarter View from Earth Result: Moon appears one-half illuminated The Moon’s phase (synodic) period is longer than its orbit (sidereal) period: 29.5 d > 27.3 d To distant stars Lunar Phase Visibility At what time of day are the various phases visible in your sky?