Moon Facts
- Earth’s only natural
satellite (Unusual).
- Takes 29.5 days to cycle
through phases.
(Synodic Month)
- Orbits the earth every
27.3 days.
(Sidereal Month)
- Rotates once per orbit.
(Synchronous orbit)
- One moon-day = 27.3 earth-days.
- Same side always faces earth.
- Wobbles slightly (Libration).
- We see 59% of moon.
- Other 41% is the “dark side”.
- 1959 Soviet spacecraft (Luna 3)
first viewed dark side.
- Average distance to moon = 239,900 miles.
- Moon is less than 1/3rd the diameter of earth.
- Only 1/80th the mass of earth.
- Gravity is 1/6 that of earth.
- We would weigh about 20-30 lbs.
- Has no atmosphere (not enough gravity).
- Temp. ranges from 266 °F to -280 °F
Moon Formation
Daughter Theory
- Moon spun off from early earth.
- Unlikely, earth probably wasn’t spinning fast enough.
Sister Theory
- Earth and moon formed separately, near each other.
- Unlikely, earth and moon rocks are different.
Captive Theory
- Moon formed away from earth, later captured.
- Unlikely, not enough gravity.
Impact Theory
- Mars-sized object hit early earth.
- Explains tilt of earth’s axis.
- Most likely theory.
Tides
- The moon’s gravitational pull affects the earth.
- 2 high and 2 low tides each day.
- Averages 3ft in open ocean.
- Moon exerts more force on closer
parts of earth.
- Creates “tidal bulges”
- Sun also affects tides.
1st Quarter, Neap Tide
Opposition, Spring Tide
Conjunction, Spring Tide
3rd Quarter, Neap Tide
- Friction of tides is causing
the earth’s rotation to slow.
- 2/1,000 of a second per century.
- Will eventually synchronize
with moon.
- Moon speeding up, spiraling away.
Moon Geology
- Surface features first observed by Galileo.
- Estimated moon-mountain height.
- Kepler named much of the terrain.
- No longer geologically active.
- No volcanoes, plate tectonics.
- Occasional small moonquakes.
- Caused by tidal forces.
- “Maria” means seas. (“mare” singular)
- Used to describe plains or flat areas.
- Made of basalt (lava-rock).
- Darker color
- Highlands (not quite mountains,
more hilly)
- Rocks are mostly anrthosite.
- Lighter color
- How do we know?
- Apollo missions brought back 800 lb
of moon rock.
- Craters (means “bowl”)
- Caused by meteroid impact
- Ejecta Blanket
- Debris from impact
- 84% cratered
- More on “dark side”
- 16% maria
- More on earth-facing side