5A5AObjectivesObjectives

List and describe some basic List and describe some basic characteristics of the moon including:characteristics of the moon including:

RotationRotation RevolutionRevolution GravityGravity SizeSize CompositionComposition Geographic featuresGeographic features Geologic featuresGeologic features

Describe the difference between apogee Describe the difference between apogee and perigeeand perigee

Discuss the various theories presented Discuss the various theories presented for the formation of the moonfor the formation of the moon

Our MoonOur Moon

Approximately ¼ our sizeApproximately ¼ our size Less dense than EarthLess dense than Earth 1/6 our gravity1/6 our gravity

– Divide your weight by 6Divide your weight by 6– That’s what you would weight on the moonThat’s what you would weight on the moon

No waterNo water No atmosphereNo atmosphere No weatherNo weather

Lunar SurfaceLunar Surface

Man in the Moon refers to…Man in the Moon refers to…– Apparent human face seen by some observers Apparent human face seen by some observers – Made up of geographical characteristics on the Made up of geographical characteristics on the

moonmoon Why do we always see the Man in the Moon?Why do we always see the Man in the Moon?

– Moon’s rotation and revolution are almost exactly Moon’s rotation and revolution are almost exactly the samethe same

– Synchronous rotationSynchronous rotation– Rotates at the same speed that it revolves Rotates at the same speed that it revolves

meaning that the same side of the moon always meaning that the same side of the moon always faces Earthfaces Earth

Rotation = about 27 daysRotation = about 27 days Revolution = about 27 daysRevolution = about 27 days

Features of the MoonFeatures of the Moon

HighlandsHighlands– Light colored regionsLight colored regions– TerraeTerrae

LowlandsLowlands– Dark colored regionsDark colored regions– MariaMaria

Features of the MoonFeatures of the Moon

Impact CratersImpact Craters– Formed from asteroids and comets Formed from asteroids and comets

colliding with the lunar surfacecolliding with the lunar surface– Half a million craters larger than 1 km Half a million craters larger than 1 km

on the moonon the moon

CratersCraters

CratersCraters

Largest crater on our moon is also Largest crater on our moon is also the largest crater in our solar systemthe largest crater in our solar system– Far side between south pole and Far side between south pole and

equatorequator– South Pole Aitken BasinSouth Pole Aitken Basin– 2240 km diameter and 13 km deep2240 km diameter and 13 km deep

South Pole Aitken BasinSouth Pole Aitken Basin

Volcanism on the MoonVolcanism on the Moon

When then moon formed, it was hot and When then moon formed, it was hot and moltenmolten

Because it is so much smaller than Because it is so much smaller than Earth, it cooled much fasterEarth, it cooled much faster

Evidence from moon rocks collected by Evidence from moon rocks collected by astronauts suggest that there were astronauts suggest that there were volcanoes on the moon at one timevolcanoes on the moon at one time

Sinuous rilles (valleys) also suggest that Sinuous rilles (valleys) also suggest that there were once volcanoes there were once volcanoes

Moon’s OrbitMoon’s Orbit

EllipticalElliptical– Therefore the moon is closer to us at Therefore the moon is closer to us at

times and farther from us at other timestimes and farther from us at other times PerigeePerigee

– When the moon is closestWhen the moon is closest– 350,000 km350,000 km

ApogeeApogee– When the moon is the farthestWhen the moon is the farthest– 400,000 km400,000 km

Previous TheoriesPrevious Theories

Fission TheoryFission Theory– Proposed by GH Darwin (Charles Darwin Proposed by GH Darwin (Charles Darwin

son)son)– The moon was spun out of the earth's The moon was spun out of the earth's

mantle during an early era of rapid rotation mantle during an early era of rapid rotation of the ancient earthof the ancient earth

– So the Earth was spinning so fast when it So the Earth was spinning so fast when it was first forming that the high velocity shot was first forming that the high velocity shot off a piece of Earth that became the moonoff a piece of Earth that became the moon

Previous TheoriesPrevious Theories

Capture TheoryCapture Theory– The moon formed somewhere else in The moon formed somewhere else in

the solar system and was later captured the solar system and was later captured in orbit about the earthin orbit about the earth

– The moon formed somewhere The moon formed somewhere (anywhere) and when it passed by the (anywhere) and when it passed by the Earth, it somehow got caught in an orbit Earth, it somehow got caught in an orbit around usaround us

Previous TheoriesPrevious Theories

Co-Accretion Theory Co-Accretion Theory (Double Planet Theory)(Double Planet Theory)– The earth and moon simply grew The earth and moon simply grew

together out of the same primordial together out of the same primordial materials in close proximity to each materials in close proximity to each otherother

Problems with the TheoriesProblems with the Theories

When we made it to the moon and When we made it to the moon and brought back moon rocks, we studied brought back moon rocks, we studied them.them.

With the evidence of lunar rocks, With the evidence of lunar rocks, their composition, oxygen isotope their composition, oxygen isotope presence, etc.presence, etc.

The previous theories were proved The previous theories were proved inaccurate.inaccurate.

New Theory – Collision New Theory – Collision TheoryTheory

The Moon was formed when a Mars-The Moon was formed when a Mars-sized object collided with the Earth sized object collided with the Earth when the Earth was very young, about when the Earth was very young, about 4.5 billion years ago4.5 billion years ago

Much of the Earth's crust and mantle, Much of the Earth's crust and mantle, along with most of the colliding along with most of the colliding object, disintegrated and was blown object, disintegrated and was blown into orbit thousands of kilometers highinto orbit thousands of kilometers high

New TheoryNew Theory

About half of this debris fell back to About half of this debris fell back to EarthEarth

The rest coalesced into the MoonThe rest coalesced into the Moon Since the time of its original Since the time of its original

formation, the Moon has slowly moved formation, the Moon has slowly moved farther from the Earth to its present farther from the Earth to its present position. position.

Origin of the MoonOrigin of the Moon

The idea in a nutshell:The idea in a nutshell: At the time Earth formed 4.5 billion At the time Earth formed 4.5 billion

years ago, other smaller planetary years ago, other smaller planetary bodies were also growing. One of bodies were also growing. One of these hit earth late in Earth's growth these hit earth late in Earth's growth process, blowing out rocky debris. A process, blowing out rocky debris. A fraction of that debris went into orbit fraction of that debris went into orbit around the Earth and aggregated into around the Earth and aggregated into the moon. the moon.