Moon phasesMoon phases

Moon Phases TermsMoon Phases Terms

�� Waxing Waxing –– moon getting biggermoon getting bigger

�� Waning Waning –– moon getting smallermoon getting smaller

�� Crescent Crescent –– moon less than half fullmoon less than half full

�� Gibbous Gibbous –– moon more than half fullmoon more than half full

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 Waxing -- Moving towards a full moonMoving towards a full moon

�� Waning Waning –– Moving towards a new moonMoving 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 = Half of half = ¼¼

�� Rises at noonRises at noon

�� Overhead at sunsetOverhead at sunset

�� Sets at midnightSets at midnight

Waxing moonsWaxing moons

Waxing 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 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 = Half of half = ¼¼

�� 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 Earth

�� Has 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 Problem –– EarthEarth’’s gravity should have s gravity should have

pulled the bulge back inpulled the bulge back in

Capture TheoryCapture Theory�� Moon formed somewhere else and was Moon formed somewhere else and was

captured by Earthcaptured by Earth’’s gravitys gravity

�� Problem Problem –– something would have to slow something would have to slow

down the moondown the moon

�� DoesnDoesn’’t explain lack of water, or moon 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 Problem –– lack of iron, lack of water, moon 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

awayawayNo ironNo iron

FissionFission

CaptureCapture

CoformationCoformation

ImpactImpact