ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon...
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Transcript of ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon...
![Page 1: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/1.jpg)
ASTR 2310: Chapter 4
Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses
![Page 2: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/2.jpg)
ASTR 2310: Chapter 4
Precession
– We talked about this already (equinoxes, Polaris...)
– Now a bit more on why...
– The Earth is not a perfect sphere (what is?!)
– The sun is not the only source of gravitational influence on the Earth
– Also very important is the moon
![Page 3: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/3.jpg)
ASTR 2310: Chapter 4
Precession
– Earth's “spare tire” plus tilt means a torque from the sun and moon. See figure in text, plus:
![Page 4: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/4.jpg)
ASTR 2310: Chapter 4
Tides, a related concept
– Depends on the idea that gravity depends on distance, and the near side of the Earth is pulled on harder than the far side (again by Sun and Moon)
– Follow derivation of tidal forces from text (p. 85-88)
![Page 5: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/5.jpg)
ASTR 2310: Chapter 4
Tides, a related concept
![Page 6: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/6.jpg)
ASTR 2310: Chapter 4
Tidal Braking
– Friction breaks symmetry, so bulge is retarded
– Earth's rotation slows, Moon orbit increases
– Math here...
![Page 7: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/7.jpg)
ASTR 2310: Chapter 4
Limits on Orbits
– Minimum: Roche Limit• Balance self gravity against tidal forces
– Maximum: Hill Radius• Balance gravity of planet (Earth) vs. Sun
– Go through the math of each on board
![Page 8: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/8.jpg)
ASTR 2310: Chapter 4 Phases of the Moon
– Video
– Figure
– Quiz
– Lab Demo
![Page 9: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/9.jpg)
ASTR 2310: Chapter 4 Facts about Moon's Orbit
– Titled by 5.1 degrees compared to the ecliptic
– Sidereal vs. Synodic months• Derivation in text, similar to things in Chapter 2
• P_syn = 29.531 days (e.g. new moon to new moon)
• P_sid = 27.322 days
![Page 10: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/10.jpg)
ASTR 2310: Chapter 4 Rotation of the Moon
– Earth exerts larger tidal forces on moon than moon does on Earth
– Tidal braking is more effective
– Moon now locked into synchronous rotation
– Issue of “Far Side” vs. “Dark Side” -- Get it right!
– Lunar Librations...see next slide/video
![Page 11: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/11.jpg)
ASTR 2310: Chapter 4 Lunar Librations
– Earth exerts larger tidal forces on moon than moon does on Earth
– Tidal braking is more effective
– Moon now locked into synchronous rotation
– Issue of “Far Side” vs. “Dark Side” -- Get it right!
– Lunar Librations...see next slide/video
![Page 12: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/12.jpg)
ASTR 2310: Chapter 4 Lunar Librations (diurnal) Video: http://www.youtube.com/watch?v=6nTmOIkUoTs
![Page 13: ASTR 2310: Chapter 4 Earth-Moon System Precession Tides Limits on Sizes of Orbits Phases of the Moon Rotation of the Moon Eclipses.](https://reader035.fdocuments.net/reader035/viewer/2022062421/56649d5f5503460f94a40084/html5/thumbnails/13.jpg)
ASTR 2310: Chapter 4 Lunar Librations (in longitude due to
eccentricity of lunar orbit, and in latitude due to orbital tilt):