Moon phasesMoon phases

What causes phases of the What causes phases of the moon?moon?

The orbit of the Moon around the Earth.The orbit of the Moon around the Earth.We can only see part of the illuminated We can only see part of the illuminated

portionportion

What do we see?What do we see?Half of the Half of the

Moon is always Moon is always illuminatedilluminated

Half of the Half of the moon always moon always faces Earthfaces Earth

Where the Where the halves overlap, halves overlap, we see phaseswe see phases

What do we see?What do we see? It takes 28 It takes 28

days for the days for the moon to make moon to make a complete a complete orbitorbit

This means the This means the cycle repeats cycle repeats once a monthonce a month

Waxing and WaningWaxing and Waning

Waxing - Moving towards a full moonWaxing - Moving towards a full moonWaning – Moving towards a new moonWaning – Moving towards a new moon

New MoonNew MoonNew moonNew moon

When the near side is When the near side is totally in shadowtotally in shadow

Rises at sunriseRises at sunrise Overhead at noonOverhead at noon Sets at sunsetSets at sunset

Waxing moonsWaxing moonsWaxing crescentWaxing crescent

Between new and first Between new and first crescentcrescent

Rises after sunriseRises after sunrise Overhead in the Overhead in the

afternoonafternoon Sets after sunriseSets after sunrise

Waxing moonsWaxing moonsFirst quarterFirst quarter

Between new and fullBetween new and full We see half of the We see half of the

illuminated halfilluminated half Half of half = ¼Half of half = ¼ Rises at noonRises at noon Overhead at sunsetOverhead at sunset Sets at midnightSets at midnight

Waxing moonsWaxing moonsWaxing GibbousWaxing Gibbous

More than quarter but More than quarter but less than fullless than full

Rises after noonRises after noon Overhead in eveningOverhead in evening Sets after midnightSets after midnight

Full MoonFull MoonFull moonFull moon

When the near side is When the near side is totally illuminatedtotally illuminated

Rises at sunsetRises at sunset Overhead at midnightOverhead at midnight Sets at sunriseSets at sunrise

Waning moonsWaning moonsWaning GibbousWaning Gibbous

Less than full, more than Less than full, more than third quarterthird quarter

Rises after sunsetRises after sunset Overhead after midnightOverhead after midnight Sets after sunriseSets after sunrise

Waning moonsWaning moonsThird quarterThird quarter

Between full and newBetween full and new We see half of the We see half of the

illuminated halfilluminated half Half of half = ¼Half of half = ¼ Rises at midnightRises at midnight Overhead in early Overhead in early

morningmorning Sets at noonSets at noon

Waning moonsWaning moonsWaning CrescentWaning Crescent

Between third quarter and Between third quarter and newnew

Rises at just before Rises at just before sunrisesunrise

Overhead just before Overhead just before noon noon

Sets just before sunsetSets just before sunset

Formation of the MoonFormation of the Moon

Where did it come from?Where did it come from?

Points to keep in mindPoints to keep in mind

Any theory of lunar formation must Any theory of lunar formation must account for:account for:The moon is as old as Earth, The moon is as old as Earth, is made of the same rock as Earthis made of the same rock as EarthHas no waterHas no water Is getting further away from Earth Is getting further away from Earth Has little ironHas little iron

Did the moon..Did the moon..

Spin off from Earth?Spin off from Earth?Form somewhere else?Form somewhere else?Form alongside Earth?Form alongside Earth?Form from an impact?Form from an impact?

Fission TheoryFission Theory

Moon spun off from a rapidly spinning Moon spun off from a rapidly spinning molten Earthmolten Earth

Problem – Earth’s gravity should have Problem – Earth’s gravity should have pulled the bulge back inpulled the bulge back in

Capture TheoryCapture TheoryMoon formed somewhere else and was Moon formed somewhere else and was

captured by Earth’s gravitycaptured by Earth’s gravityProblem – something would have to slow Problem – something would have to slow

down the moondown the moonDoesn’t explain lack of water, or moon Doesn’t explain lack of water, or moon

moving awaymoving away

Coformation TheoryCoformation Theory

Moon and Earth formed side by side from Moon and Earth formed side by side from same accretion disk.same accretion disk.

Problem – lack of iron, lack of water, moon Problem – lack of iron, lack of water, moon moving awaymoving away

Earth would have cleared its orbitEarth would have cleared its orbit

Giant Impact theoryGiant Impact theory

Mars sized planetoid impacted Earth.Mars sized planetoid impacted Earth.Moon formed from debris cloud.Moon formed from debris cloud.Most accepted theoryMost accepted theory

Giant Impact TheoryGiant Impact Theory

How do they stack upHow do they stack up

TheoryTheory AgeAge CompositionComposition No waterNo water Moving Moving awayaway

No ironNo iron

FissionFission

CaptureCapture

CoformationCoformation

ImpactImpact