The Moon Astronomy 311 Professor Lee Carkner Lecture 13

Temperature of Earth  Temp of Earth from energy balance  T E = [R S /(2 D S )] ½ T S  T E = [6.96X10 8 / (2)(1.496X10 11 )] ½ (5778)  T E = K  T F = 1.8T K -460 = (1.8)(278.7)-460  T F = 41.6 F  Actual Earth temp = 288 K  T = (1.8)(288)-460 = 58.4 F  Earth has an atmosphere, not all of the energy radiated by the Earth gets out

Temperature of Earth  How much energy does Earth emit?  P =  AT 4 =  4  R E 2 T 4  P = (5.67X10 -8 )(4  )(6.38X10 6 ) 2 (288) 4  P = 1.995X10 17 W  What happens if diameter of Earth doubles?  Earth emits more energy  But, Earth also absorbs more energy  T does not depend on Earth size  T E = [R S /(2 D S )] ½ T S

Luna -- The Goddess of the Moon   Since ancient times the Moon has been thought to affect behavior (“lunatic”, “moonstruck”)  There is no good evidence for this however

Principle Features of the Moon  Maria   maria is Latin for seas  arrangement of maria produces the “man-in-the- moon”  Highlands   Craters  circular impact structures  range in size from few hundred km to microscopic

Moon Facts  Size: 3476 km diameter   Orbit: 384,000 km   Description: small, airless, cratered  surface is similar to Mercury

Timeline of Moon Exploration  Luna 1 (USSR, 1959) first spacecraft to fly by the Moon  Luna 2 (USSR, 1959)  Luna 9 (USSR, 1966) first lunar lander  Luna 10 (USSR, 1966)  Apollo 8 (USA, 1968) first manned orbiter  Apollo 11 (USA, 1969)  Luna 16 (USSR), 1970) first automated sample return

Near and Far Sides of the Moon

Why is the Moon Airless?   Gravity   Thermal motions   All molecules have a velocity proportional to their temperature  The Moon has no atmosphere because this velocity is too large for its gravity to overcome

The Surface of the Moon  Maria:  covered with dark colored mare basalt   similar to lava on Earth  Highlands:  covered with light colored anorthosite   very old (more than 4 billion years)   Moon rocks are similar in many ways to Earth rocks, but are depleted in volatiles

Mare Basalt and Anorthosite

Tycho and Rays

Falling Bodies  Real impactors get their energy from their very high orbital velocities   A body dropped from a height has potential energy: PE = mgh   1000 grams = 1 kg   g = 9.8 m/s 2  h is the height above the surface in meters

Energy  KE = ½mv 2  Where v is the velocity at impact in meters per second   The kinetic energy at impact must equal the potential energy at the drop point

The Moon’s Interior   Moon is much less active than the Earth   Moon is much less dense than the Earth   Moon once had a magnetic field but does not today, indicating that the core has solidified

Inside The Moon

Moon Formation Theories

Collisional Ejection Theory    The collision put large amounts of debris in orbit, which formed into the Moon   Energy from impact depleted the Moon in volatiles  The ejected material was mostly mantle rock, so the Moon has a very small core

A History of the Moon  4.6 billion years ago:   billion years ago:   ~3.8 billion years ago:  large impacts produce mare basins  billion years ago:   3 billion years ago- present  core solidified, no more magnetic field  small amounts of cratering 

Next Time  Read Chapter 10

Summary  Moon was formed 4.6 billion years ago when large impactor hit the Earth  Moon has a low density because it has only a small iron core  Moon has become tidally lock so that only the near-side faces Earth  Most of our information about the Moon comes from the Apollo missions

Summary: Surface  Maria  large impacts produced basins which then filled with lava  darker, denser and younger than the highlands  Highlands  regions that have not experienced large impacts or lava  lighter, less dense and older than the Maria  Large numbers of impacts have covered the surface with craters and regolith (dust)