PHY 113 Lecture Notes - Lecture 8: Computer Simulation, Tidal Locking, Escape Velocity
9 Jun 2018
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Chapter 8
The Moon and Mercury
8.1 Orbital Properties
8.2 Physical Properties
8.3 Surface Features on the Moon and Mercury
8.4 Rotation Rates Lunar Exploration
Why Air Sticks Around
8.5 Lunar Cratering and Surface Composition
Units of Chapter 8 (cont.)
8.6 The Surface of Mercury 8.7 Interiors
8.8 The Origin of the Moon
8.9 Evolutionary History of the Moon and Mercury
8.1 Orbital Properties
Distance between Earth and Moon has been measured to accuracy of a few centimeters using
lasers
Viewed from Earth, Mercury is never far from the Sun
be seen best when Mercury is at its maximum elongation (apparent distance from Sun)
8.3 Surface Features on the Moon and Mercury
Moon has large dark flat areas, due to lava flow, called maria (early observers thought they
were oceans)
Moon also has many craters (from meteorite impacts)
Far side of Moon has some craters but no maria
Important indicator that maria are somehow related to facing Earth-side
Mercury cannot be imaged well from Earth; best pictures are from Messenger
Cratering on Mercury is similar to that on Moon
8.4 Rotation Rates
Moon is tidally locked to Earth—its rotation rate is the same as the time it takes to make one
revolution, so the same side of the Moon always faces Earth
Moon also slightly elongated towards Earth.
Crust is thicker on the far side than the near side (kind of similar to ocean tides)
Near side, easier for lava/mantle to escape Maria
Mercury was long thought to be tidally locked to the Sun; measurements in 1965 showed this
to be false.
Rather, Mercury’s day and year are in a 3:2 resonance; Mercury rotates three times while
going around the Sun twice.
Mercury’s orbit is pretty eccentric (compared to other planets). So could it be tidally locked
all the time?
The resonance means the same axis (the elongated axis of Mercury) always faces the Sun
when it’s closest (perihelion).
Discovery 8-1: Lunar
Exploration
Soviets had first contact with Moon:
• First spacecraft to fly past Moon: January 1959
• First spacecraft to (crash) land on Moon: September 1959
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Document Summary
8. 9 evolutionary history of the moon and mercury. Distance between earth and moon has been measured to accuracy of a few centimeters using lasers. Viewed from earth, mercury is never far from the sun be seen best when mercury is at its maximum elongation (apparent distance from sun) 8. 3 surface features on the moon and mercury. Moon has large dark flat areas, due to lava flow, called maria (early observers thought they were oceans) Moon also has many craters (from meteorite impacts) Far side of moon has some craters but no maria. Important indicator that maria are somehow related to facing earth-side. Mercury cannot be imaged well from earth; best pictures are from messenger. Cratering on mercury is similar to that on moon. Moon is tidally locked to earth its rotation rate is the same as the time it takes to make one revolution, so the same side of the moon always faces earth.
