The Earth-Moon-Sun The Earth-Moon-Sun SystemSystem

Earth’s MoonEarth’s Moon

• It takes 27.3 days for the Moon to It takes 27.3 days for the Moon to revolve once around Earthrevolve once around Earth

• Because Earth also revolves around Because Earth also revolves around the Sun, it takes more than two more the Sun, it takes more than two more days for the Moon to line up with days for the Moon to line up with Earth and the SunEarth and the Sun

• A complete lunar phase cycle takes A complete lunar phase cycle takes 29.5 days29.5 days

The Moon keeps the same side The Moon keeps the same side facing Earth because it takes 27.3 facing Earth because it takes 27.3 days to rotate once on its axisdays to rotate once on its axis•

• Why is the same side of the Moon Why is the same side of the Moon always facing the Earth?always facing the Earth?

• The Moon’s period of revolution and The Moon’s period of revolution and period of rotation are the sameperiod of rotation are the same

How does the Moon affect How does the Moon affect Earth?Earth?

• A tide on Earth is caused by a giant A tide on Earth is caused by a giant wave produced by the gravitational wave produced by the gravitational pulls of the Sun and the Moonpulls of the Sun and the Moon

• This rise of sea level is called high This rise of sea level is called high tidetide

• About six hours later, as the trough About six hours later, as the trough of the wave approaches, sea level of the wave approaches, sea level drops, causing a low tidedrops, causing a low tide

There are different types of There are different types of tidestides

• The Sun is much The Sun is much fartherfarther

• Because of this, the Because of this, the Moon has greater Moon has greater effect on Earth’s effect on Earth’s tides than the Suntides than the Sun

• When the Moon and When the Moon and the Sun pull the Sun pull together, high tides together, high tides are much higher and are much higher and low tides are much low tides are much lowerlower– This is called a spring This is called a spring

tidetide

Neap tideNeap tide

• What happens to the sea level at What happens to the sea level at spring tidespring tide

• High tides are higher and low tides High tides are higher and low tides are lowerare lower

MoonlightMoonlight

• Moon phases are the changing Moon phases are the changing appearances of the Moon as seen appearances of the Moon as seen from Earthfrom Earth

• The phase you see depends on the The phase you see depends on the relative positions of the Moon, Earth relative positions of the Moon, Earth and Sunand Sun

• A new moon occurs when the Moon is A new moon occurs when the Moon is between Earth and the Sunbetween Earth and the Sun

• The side of the Moon facing away The side of the Moon facing away from Earth is lighted and the side of from Earth is lighted and the side of the Moon facing Earth receives no the Moon facing Earth receives no light from the Sunlight from the Sun

• Waxing – the lighted portion that we see Waxing – the lighted portion that we see appears larger each nightappears larger each night

• The first phase we see after a new moon is The first phase we see after a new moon is called the waxing crescentcalled the waxing crescent

• About a week after a new moon is the first About a week after a new moon is the first quarterquarter

• The moon is in the waxing gibbous phase The moon is in the waxing gibbous phase from the first quarter up until the full from the first quarter up until the full moonmoon

• After a full moonAfter a full moon, , the lighted portion the lighted portion that we see begins to appear smallerthat we see begins to appear smaller– The phases are said to be waningThe phases are said to be waning

• When only half of the side of the When only half of the side of the Moon facing Earth is lighted, the third Moon facing Earth is lighted, the third quarter phase occursquarter phase occurs

• The waning crescent occurs before The waning crescent occurs before another new moonanother new moon

•The word month is derived The word month is derived from the same root word as from the same root word as MoonMoon

EclipsesEclipses

• A solar eclipse A solar eclipse occurs when the occurs when the Moon moves Moon moves directly between directly between the Sun and Earth the Sun and Earth and casts a shadow and casts a shadow on part of Earthon part of Earth

• The darkest part of The darkest part of the Moon’s shadow the Moon’s shadow is called the umbrais called the umbra

• When Earth’s When Earth’s shadow falls on the shadow falls on the Moon, a lunar Moon, a lunar eclipse occurseclipse occurs

• A partial lunar A partial lunar eclipse occurs eclipse occurs when only a portion when only a portion of the Moon moves of the Moon moves into Earth’s umbrainto Earth’s umbra

The Moon’s SurfaceThe Moon’s Surface

• Meteorites, Meteorites, asteroids and asteroids and comets formed the comets formed the many depressions many depressions that are on the that are on the MoonMoon

• These depressions These depressions are called cratersare called craters

• Maria are the dark colored relative Maria are the dark colored relative flat regions on the Moon’s surfaceflat regions on the Moon’s surface

• Surrounding the large depressions Surrounding the large depressions that later filled with lava are areas that later filled with lava are areas that were thrown upward in the that were thrown upward in the original collisions and formed original collisions and formed mountainsmountains

• Impacts on the Moon throughout its Impacts on the Moon throughout its history led to accumulation of debris history led to accumulation of debris that is known as regoliththat is known as regolith

• The Moon’s crust is The Moon’s crust is 60 km thick on the 60 km thick on the side facing Earth side facing Earth and about 150 km and about 150 km on the side facing on the side facing awayaway

• A solid mantle may A solid mantle may extend to a depth extend to a depth of 1000 kmof 1000 km

• A partially molten zone of mantle A partially molten zone of mantle extends even further downextends even further down

• Below the molten zone is an iron-Below the molten zone is an iron-rich, solid corerich, solid core

Exploring the MoonExploring the Moon• Data from Data from ClementineClementine confirmed that confirmed that

the crust on the side facing Earth is the crust on the side facing Earth is much thinner than on the far sidemuch thinner than on the far side– It also provided information on the mineral It also provided information on the mineral

content of Moon rockscontent of Moon rocks

• The The Lunar ProspectorLunar Prospector spacecraft orbited spacecraft orbited the Moon, taking pictures of the surfacethe Moon, taking pictures of the surface– It also confirmed that the Moon has a small, It also confirmed that the Moon has a small,

iron-rich core about 600 km in diameteriron-rich core about 600 km in diameter

Origin of the MoonOrigin of the Moon

• Giant Impact TheoryGiant Impact Theory– The Moon formed about 4.6 BILLION years ago The Moon formed about 4.6 BILLION years ago

when a Mars-sized object collided with Earthwhen a Mars-sized object collided with Earth– After colliding, the cores of the two bodies After colliding, the cores of the two bodies

combined and settled toward the center of the combined and settled toward the center of the larger objectlarger object

– Gas and other debris were thrown into orbitGas and other debris were thrown into orbit– The remainder condensed into a large mass, The remainder condensed into a large mass,

forming the Moonforming the Moon