EarthEarth’’s Moon s Moon and Solar Systemand Solar System

Phases of the MoonPhases of the Moon

The apparent shape of the moon depends The apparent shape of the moon depends upon the changing relative positions of Earthupon the changing relative positions of Earth

As the moon completes one revolution As the moon completes one revolution around Earth each month, the growing and around Earth each month, the growing and shrinking lighted area makes the moon shrinking lighted area makes the moon appear to change in shapeappear to change in shape

The moonThe moon’’s periods of rotation and revolution s periods of rotation and revolution are equalare equalBecause of this, the same side of the moon Because of this, the same side of the moon

always faces Earthalways faces Earth

Phases of the MoonPhases of the Moon

One complete orbit of the moon around One complete orbit of the moon around Earth takes about 27 daysEarth takes about 27 days

A complete cycle of the moonA complete cycle of the moon’’s phases s phases takes 29 ½ daystakes 29 ½ daysThis 2 ½ day difference occurs because as the This 2 ½ day difference occurs because as the

moon orbits Earth, Earth orbits the sunmoon orbits Earth, Earth orbits the sunWhen the moon gets back to its original When the moon gets back to its original

position, it must move through an extra angle of position, it must move through an extra angle of about 30° to compensate for Earthabout 30° to compensate for Earth’’s orbital s orbital motion around the sunmotion around the sun

Eclipse of the MoonEclipse of the Moon

An An eclipseeclipse of the moon occurs when the full of the moon occurs when the full moon moves into Earthmoon moves into Earth’’s shadows shadow

During a lunar eclipse, the moon turns a During a lunar eclipse, the moon turns a coppery redcoppery redYou can still see the You can still see the

moon because sunlight moon because sunlight is bent by Earthis bent by Earth’’s s atmosphere, which atmosphere, which causes a weak causes a weak illumination of the moonillumination of the moon

Eclipse of the SunEclipse of the Sun

An An eclipseeclipse of the sun occurs when the new of the sun occurs when the new moon briefly moves in front of the sunmoon briefly moves in front of the sun

At this time the At this time the moon casts its moon casts its shadow on Earthshadow on Earth

Angular DiameterAngular Diameter

Angular diameter is the angle formed Angular diameter is the angle formed between the sides of an object and your eyebetween the sides of an object and your eye

The angular diameter of any object depends The angular diameter of any object depends upon the actual upon the actual size of the size of the object and object and how far away how far away it is from it is from the observerthe observer

Angular Diameter of the SunAngular Diameter of the Sun

Observations of the sunObservations of the sun’’s angular diameter s angular diameter tell us that Earth is closest to the sun in tell us that Earth is closest to the sun in January and farthest from the sun in JulyJanuary and farthest from the sun in July

Seasonal variations result from the tilt of the Seasonal variations result from the tilt of the EarthEarth’’s axis and Earths axis and Earth’’s shape not from s shape not from Earth-sun distanceEarth-sun distance

The sunThe sun’’s angular diameter is larger in s angular diameter is larger in winter and smaller in summerwinter and smaller in summer

Angular Size and Shape of OrbitAngular Size and Shape of Orbit

Because the moon seems to change size Because the moon seems to change size more than the sun, we can infer that changes more than the sun, we can infer that changes in the relative distance between the moon in the relative distance between the moon and Earth are greater than changes in the and Earth are greater than changes in the relative distance between the sun and Earthrelative distance between the sun and Earth

Since both changes are small compared to Since both changes are small compared to the magnitude of the average distance, we the magnitude of the average distance, we can infer that the orbit of the moon around can infer that the orbit of the moon around Earth and the orbit of Earth around the sun Earth and the orbit of Earth around the sun are nearly circularare nearly circular

Earth-Moon OrbitEarth-Moon Orbit

The TidesThe Tides

Every point along the ocean experiences Every point along the ocean experiences two low tides and two high tides per daytwo low tides and two high tides per day

The difference between high tide and low The difference between high tide and low tide is usually less than a meter (3 feet)tide is usually less than a meter (3 feet)

The cause of tides is gravitational attraction The cause of tides is gravitational attraction off the moon and the sunoff the moon and the sunThe sun and moon pull on the water in the The sun and moon pull on the water in the

oceans and on the solid part of Earthoceans and on the solid part of Earth

The TidesThe Tides

The water of the oceans is pulled toward The water of the oceans is pulled toward the moon, which causes high tidethe moon, which causes high tide

Another high tide occurs on the opposite Another high tide occurs on the opposite side of Earth, where the solid part of Earth side of Earth, where the solid part of Earth is pulled away from the oceansis pulled away from the oceans

The highest high tides and the lowest low The highest high tides and the lowest low tides occur about twice a month near the tides occur about twice a month near the full and new moon phasesfull and new moon phases

The TidesThe Tides

The Geometry of OrbitsThe Geometry of OrbitsPlanets revolve in an Planets revolve in an ellipseellipse around the sun around the sun

An ellipse has two fixed points called foci that An ellipse has two fixed points called foci that are on either side of the center of the axisare on either side of the center of the axis

The sun lies at one focus and is not the center The sun lies at one focus and is not the center of Earthof Earth’’s orbits orbit

The Geometry of OrbitsThe Geometry of Orbits If the two foci are located If the two foci are located

near the ends of the axis, an near the ends of the axis, an ellipse is long and narrowellipse is long and narrow

Many comets have Many comets have this type of paththis type of path

If the foci move closer If the foci move closer together, the shape of the together, the shape of the ellipse becomes circularellipse becomes circular

Calculating Eccentricity Calculating Eccentricity (elongation) of an ellipse(elongation) of an ellipse

Eccentricity = Eccentricity = distance between the focidistance between the foci

length of the major axislength of the major axis

e = d/Le = d/L

The Force of GravityThe Force of Gravity

GravityGravity is a force of attraction between is a force of attraction between objects that is dependent on the masses objects that is dependent on the masses of the objects and the distance between of the objects and the distance between themthem

Gravity and the PlanetsGravity and the Planets

GravityGravity is the force that holds the planets is the force that holds the planets and other objects in the solar system in and other objects in the solar system in their orbitstheir orbits

Any object that orbits another object in Any object that orbits another object in space is known as a space is known as a satellitesatelliteEarth is a satellite of the sunEarth is a satellite of the sunThe moon is EarthThe moon is Earth’’s satellites satellite

Gravity and the PlanetsGravity and the PlanetsThe elliptical path The elliptical path

of any satellite is of any satellite is a result of a result of inertiainertia and and gravitygravity InertiaInertia is the is the

tendency of an tendency of an object to remain object to remain at rest, or, if it is at rest, or, if it is moving, to move moving, to move with the same with the same speed in the speed in the same directionsame direction

Gravity and the PlanetsGravity and the Planets If a satellite has a circular orbit, inertia and If a satellite has a circular orbit, inertia and

the force of gravity are constantthe force of gravity are constantThere is no change in speed, but there is a There is no change in speed, but there is a

constant change in direction, producing a constant change in direction, producing a circular pathcircular path

Gravity and the PlanetsGravity and the Planets If a satellite has If a satellite has

an elliptical orbit, an elliptical orbit, gravity causes the gravity causes the speed to changespeed to changeThe satellite will The satellite will

move faster when move faster when itit’’s near its s near its primary and primary and slower when itslower when it’’s s farther awayfarther away

Gravity and the PlanetsGravity and the PlanetsThe closer a planet is to the sun, the faster The closer a planet is to the sun, the faster

it moves in its orbitit moves in its orbitMercury, the planet closest to the sun, travels Mercury, the planet closest to the sun, travels

about 1.6 times as fast as Earth and 10 times about 1.6 times as fast as Earth and 10 times the speed of Plutothe speed of Pluto

Planets of our Solar SystemPlanets of our Solar System

The planets can be divided into two groupsThe planets can be divided into two groupsRocky (terrestrial) planets Rocky (terrestrial) planets

MercuryMercuryVenusVenusEarth (density = 5.5 g/cmEarth (density = 5.5 g/cm33))

Gas giantsGas giantsJupiterJupiterSaturnSaturnUranusUranusNeptuneNeptune

Planets of our Solar SystemPlanets of our Solar System

Similarities Between Similarities Between Mercury and EarthMercury and Earth’’s Moons Moon

Both the moon and Mercury are smaller than EarthBoth the moon and Mercury are smaller than Earth Both have a dark surface covered with craters from Both have a dark surface covered with craters from

meteoritesmeteorites Neither have a significant atmosphereNeither have a significant atmosphere

They are not protected from meteor impacts and their They are not protected from meteor impacts and their craters do not erode quicklycraters do not erode quickly

Soil samples would show no chemical weatheringSoil samples would show no chemical weathering They both have extreme temperaturesThey both have extreme temperatures

Both have very slow rotations making days and Both have very slow rotations making days and nights longer than on Earthnights longer than on Earth

Planet Surface TemperaturesPlanet Surface Temperatures Are a result of the distance from the SunAre a result of the distance from the Sun

Hottest Planets are Mercury and VenusHottest Planets are Mercury and Venus

Venus is a little hotter due to a very dense Venus is a little hotter due to a very dense atmosphere of carbon dioxide producing a atmosphere of carbon dioxide producing a ““greenhouse effectgreenhouse effect””

Earth and Mars are cooler because of the greater Earth and Mars are cooler because of the greater distance from the sundistance from the sun Mars has a very thin atmosphere of mostly carbon Mars has a very thin atmosphere of mostly carbon

dioxide with minimal dioxide with minimal ““greenhouse effectgreenhouse effect””

The gas giant planets do not have The gas giant planets do not have ““surface surface temperaturestemperatures”” as they are composed of gases as they are composed of gases that increase in density with depth and pressurethat increase in density with depth and pressure

Earth is UniqueEarth is UniqueEarth is the only planet that has abundant Earth is the only planet that has abundant

liquid waterliquid waterThe presence of liquid water on Earth may The presence of liquid water on Earth may

be the reason why living organisms have not be the reason why living organisms have not been detected elsewhere in the solar systembeen detected elsewhere in the solar system

The EarthThe Earth’’s atmosphere is the only planet s atmosphere is the only planet that has an atmosphere with abundant free that has an atmosphere with abundant free oxygen that is released when plants extract oxygen that is released when plants extract carbon from carbon dioxide by carbon from carbon dioxide by photosynthesisphotosynthesis

AsteroidsAsteroidsLocated mostly between Mars and Jupiter Located mostly between Mars and Jupiter

in a belt of thousands of rocky objectsin a belt of thousands of rocky objectsThey range from the size of pebbles to They range from the size of pebbles to

600 miles in diameter600 miles in diameterA few have orbits that A few have orbits that

can cross Earthcan cross Earth’’s orbits orbit

MeteorsMeteorsSmall solid particles from Small solid particles from

space can be caught by space can be caught by EarthEarth’’s gravity and dragged s gravity and dragged down through the atmospheredown through the atmosphere

As the objects fall, they are heated by As the objects fall, they are heated by friction with the Earth atmosphere and friction with the Earth atmosphere and burn up, producing streaks of light burn up, producing streaks of light ((““shooting starsshooting stars””) visible at night) visible at night

Meteors that survive their fall and hit the Meteors that survive their fall and hit the ground are called ground are called meteoritesmeteorites

CometsComets Icy objects which usually originate in a region Icy objects which usually originate in a region

outside of the planetsoutside of the planetsSome of them come close to the sun in very Some of them come close to the sun in very

elliptical orbitselliptical orbitsHeating by the sun causes them to partially Heating by the sun causes them to partially

vaporize producing a tailvaporize producing a tailComets are visible for Comets are visible for

weeks and do not weeks and do not streak across the streak across the night skynight sky

The SunThe Sun The nearest star to EarthThe nearest star to Earth

A A starstar is a large, self-luminous body in space that is a large, self-luminous body in space that creates its own energycreates its own energy

The sun gets its energy from nuclear fusionThe sun gets its energy from nuclear fusion Dark spots on the sunDark spots on the sun’’s surface are known as s surface are known as

sunspotssunspots Sunspots are temporary Sunspots are temporary

storms visible on the storms visible on the surface of the sunsurface of the sun

Sunspots come Sunspots come and go in cycles and go in cycles of about 11 yearsof about 11 years

Classifying StarsClassifying Stars

The The Hertzprung-Russell diagramHertzprung-Russell diagram is used is used to classify stars by temperature and sizeto classify stars by temperature and size

Our sun is a fairly typical starOur sun is a fairly typical starAlthough the sun Is brighter than most of Although the sun Is brighter than most of

the nearest stars, it is small compared with the nearest stars, it is small compared with most of the stars we see at nightmost of the stars we see at night

GalaxiesGalaxiesA galaxy is a huge body of stars and other A galaxy is a huge body of stars and other

matter in spacematter in spaceOur own galaxy is Our own galaxy is

called the called the Milky Way Milky Way named for its named for its faint white colorfaint white color

The sun is one The sun is one of about 100 billion of about 100 billion stars in the stars in the Milky WayMilky Way

The Milky WayThe Milky Way The Milky Way is a spiral galaxyThe Milky Way is a spiral galaxy Our solar system is Our solar system is

located in a spiral arm located in a spiral arm well away from the well away from the galactic centergalactic center

The Earth and sun and The Earth and sun and other nearby stars orbit other nearby stars orbit around the center of the around the center of the Milky Way galaxyMilky Way galaxy It takes about 220 million It takes about 220 million

years to complete this years to complete this revolutionrevolution

SpectroscopesSpectroscopesThe light given off by stars is marked by The light given off by stars is marked by

dark lines in certain colorsdark lines in certain colorsA A spectroscopespectroscope is an instrument that is an instrument that

separates light into its component colorsseparates light into its component colorsSince stars are primarily hydrogen and Since stars are primarily hydrogen and

helium, the lines helium, the lines we usually see we usually see are in the orange, are in the orange, yellow, green yellow, green and blue areasand blue areas

Edwin HubbleEdwin Hubble In the early part of the 20In the early part of the 20thth century, Edwin Hubble century, Edwin Hubble

discovered that light that reached Earth from discovered that light that reached Earth from distant galaxies shows special lines that are distant galaxies shows special lines that are shifted toward the red end of the spectrumshifted toward the red end of the spectrum

He suggested that the He suggested that the red-shiftedred-shifted lines are lines are evidence that distant galaxies are moving away evidence that distant galaxies are moving away from us from us Observations of distant Observations of distant

galaxies in all directions galaxies in all directions showed the red shiftshowed the red shift

The more distant the The more distant the galaxy, the greater the galaxy, the greater the red shiftred shift

Evolution of the UniverseEvolution of the Universe The red-shift and other observations led scientists The red-shift and other observations led scientists

to the conclusion that the universe is expandingto the conclusion that the universe is expanding Computer models that reverse the expansion, lead Computer models that reverse the expansion, lead

to the idea that at one time the universe was a to the idea that at one time the universe was a concentrated object of incredible mass and density concentrated object of incredible mass and density that exploded.that exploded.

This theory of the origin of the universe is known as This theory of the origin of the universe is known as the the ““big bangbig bang”” Scientists can detect radiation Scientists can detect radiation

remaining from the big bangremaining from the big bang

Scientists currently believe the universe Scientists currently believe the universe is about 10 to 15 billion years oldis about 10 to 15 billion years old

The Size of the UniverseThe Size of the Universe The distance light can travel in one year is called The distance light can travel in one year is called

a a light-yearlight-year, which is about 10 trillion kilometers, which is about 10 trillion kilometersLight could circle Earth seven times in one secondLight could circle Earth seven times in one secondLight takes about one and a half seconds to get to Light takes about one and a half seconds to get to

the moon the moon Light from the sun takes about eight minutes to Light from the sun takes about eight minutes to

reach earthreach earthLight from the nearest star (not our sun) takes Light from the nearest star (not our sun) takes

about four years to reach usabout four years to reach us The universe is thought to be about 25 billion The universe is thought to be about 25 billion

light-years in diameterlight-years in diameter

The Future of the UniverseThe Future of the Universe

Some astronomers think that the expansion Some astronomers think that the expansion of the universe will continue foreverof the universe will continue forever

Some astronomers believe the force of Some astronomers believe the force of gravity will eventually reverse the expansion gravity will eventually reverse the expansion and the universe will fall back together in the and the universe will fall back together in the ““big crunchbig crunch””

Some astronomers think it is possible that Some astronomers think it is possible that the universe will pulsate between explosions the universe will pulsate between explosions and contractionsand contractions