O! Swear not by the moon, the inconstant moon, That monthly changes in her circled orb, Lest that thy love prove likewise variable. William Shakespeare, Romeo and Juliet

Assignment: Reading: Checkout the following pages on the the Apollo program to land men on the the Moon: Chapter 2 (pages 2.1-2.5), "I Believe We Should Go to The Moon," and Chapter 11 (pages 11.1-11.7), "The Eagle Has Landed" (Both Chapters are from NASA's text, "Apollo Expeditions to the Moon," edited by Edgar M. Cortright) Sign up for a time slot for Observing Lab #2. Problem Set #6 is due TOMORROW at 1:00 pm

In Class: Question to Ponder Occasionally, parts of the outer bits of the Sun can explode and substantially increase the number of particles in the solar wind for a short time. The particles released by these "coronal mass ejections" are generally fast movers, with speeds of 700 km/s or more (typical solar wind particles move at about 400 km/s). Based on this information, how long after a "coronal mass ejection" is seen on the Sun will the particles released reach the Earth? (1 A.U. = 1.5 x 108 km) a) About eight minutes b) About an hour c) About a day d) About two days e) About a week Why Isn't the Moon More Like Earth? Same distance from the Sun. (Roughly) the same composition. The big difference is size. Why Does Size Matter? Size determines interior temperature. Small planets cool faster, and have less radioactive heating. So no plate tectonics, and no atmosphere production. Doesn't really matter anyway, since because the Moon's small, it's gravity is weak -- too weak, in fact, to retain any gaseous atmosphere. With no atmosphere, liquid surface water isn't possible. The water will boil away even at low temperatures with no surrounding air pressure. So What Happens on The Moon? Not much. It's an airless, waterless, barren place. Only real surface evolution comes from meteorite impacts. Impacts create craters and pulverize the surface into a fine dust layer. Formation of the Moon Two reasonable possibilities: capture and Earth impact. Capture isn't likely because it's hard and typically would result in a moon with a highly eccentric orbit. Earth impact involves a glancing blow onto the early Earth by a Mars-sized object. Most of the impactor's mass becomes a part of the Earth, but a small amount could be ejected by the impact into orbit around the Earth. Explains why the moon has so little iron (e..g, material that made the Moon was blasted off the outer layers of the Earth, where there's little iron). Detailed calculations show that such a scenario is plausible. The Moon Since Formation Evolution via impacts. About 3.5-3.9 billion years ago, the Moon was pretty much fully formed. At that time, it's core was probably stll hot enough to be molten. The Moon was gravitationally differentiated, and the crust was rocky material, seen today as the bright highlands region. A few massive impactors hit the Moon --- not quite big enough to destroy it, but big enough to crack its crust and allow the molten interior to seep out. Interior stuff seeps out, forms big lava lakes, and cools to form the flat maria.