5AObjectives • List and describe some basic characteristics of the moon including: • Rotation Revolution • Gravity Size • Composition Geographic features • Geologic features • Describe the difference between apogee and perigee • Discuss the various theories presented for the formation of the moon
Our Moon • Approximately ¼ our size • Less dense than Earth • 1/6 our gravity • Divide your weight by 6 • That’s what you would weight on the moon • No water • No atmosphere • No weather
Lunar Surface • Man in the Moon refers to… • Apparent human face seen by some observers • Made up of geographical characteristics on the moon • Why do we always see the Man in the Moon? • Moon’s rotation and revolution are almost exactly the same • Synchronous rotation • Rotates at the same speed that it revolves meaning that the same side of the moon always faces Earth • Rotation = about 27 days • Revolution = about 27 days
Features of the Moon • Highlands • Light colored regions • Terrae • Lowlands • Dark colored regions • Maria
Features of the Moon • Impact Craters • Formed from asteroids and comets colliding with the lunar surface • Half a million craters larger than 1 km on the moon
Craters • Largest crater on our moon is also the largest crater in our solar system • Far side between south pole and equator • South Pole Aitken Basin • 2240 km diameter and 13 km deep
Volcanism on the Moon • When then moon formed, it was hot and molten • Because it is so much smaller than Earth, it cooled much faster • Evidence from moon rocks collected by astronauts suggest that there were volcanoes on the moon at one time • Sinuous rilles (valleys) also suggest that there were once volcanoes
Moon’s Orbit • Elliptical • Therefore the moon is closer to us at times and farther from us at other times • Perigee • When the moon is closest • 350,000 km • Apogee • When the moon is the farthest • 400,000 km
Previous Theories • Fission Theory • Proposed by GH Darwin (Charles Darwin son) • The moon was spun out of the earth's mantle during an early era of rapid rotation of the ancient earth • So the Earth was spinning so fast when it was first forming that the high velocity shot off a piece of Earth that became the moon
Previous Theories • Capture Theory • The moon formed somewhere else in the solar system and was later captured in orbit about the earth • The moon formed somewhere (anywhere) and when it passed by the Earth, it somehow got caught in an orbit around us
Previous Theories • Co-Accretion Theory (Double Planet Theory) • The earth and moon simply grew together out of the same primordial materials in close proximity to each other
Problems with the Theories • When we made it to the moon and brought back moon rocks, we studied them. • With the evidence of lunar rocks, their composition, oxygen isotope presence, etc. • The previous theories were proved inaccurate.
New Theory – Collision Theory • The Moon was formed when a Mars-sized object collided with the Earth when the Earth was very young, about 4.5 billion years ago • Much of the Earth's crust and mantle, along with most of the colliding object, disintegrated and was blown into orbit thousands of kilometers high
New Theory • About half of this debris fell back to Earth • The rest coalesced into the Moon • Since the time of its original formation, the Moon has slowly moved farther from the Earth to its present position.
Origin of the Moon • The idea in a nutshell: • At the time Earth formed 4.5 billion years ago, other smaller planetary bodies were also growing. One of these hit earth late in Earth's growth process, blowing out rocky debris. A fraction of that debris went into orbit around the Earth and aggregated into the moon.