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5/12/15 19.1 Sun, Earth, and Moon
Chapter 19: The Solar System
•  Key Ideas:
•  Why does the night sky look the way it does from
Earth?
•  What objects make up the solar system?
•  How does the moon affect Earth?
Physical Science
Doerfler
Key Terms
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Planet
Solar system
Satellite
Phase
Eclipse
19.1 Bellringer •  Earth moves around the sun, and the moon moves
around Earth. What force keeps these bodies in
their paths?
•  Gravity
Why it Ma@ers
•  Studying the solar system and its various planets can
help us understand our own planet better
The View from Earth
•  From now to six months from now, the stars that you
see will be different
•  Some star groups move across the sky in just a few
hours
•  The positions of objects in the sky change over time
because Earth, and everything else in the universe,
is constantly moving
•  Planet – celestial body that orbits the sun, is round
because of its own gravity, and has cleared the
area around its orbital path
1 5/12/15 Sun is Closest Star to Earth
•  Took thousand of years to realize sun is a star
•  Our atmosphere scatters sunlight, making it too
bright to see the other stars
•  Sun is average star:
o  Not particularly hot or cool
o  Average size
•  Diameter is 1.4 million kilometers (nearly 870,000 mi)
•  Sun’s mass is about 330,000 times that of Earth’s
Nature Uses Sun to Set Daily Cycles
•  Sun is major external source of heat and light for
Earth
•  Many patterns of animal and human life, such as
rising in the morning, eating meals at certain times,
and sleeping at night, follow the sun’s cycles
o  Called circadian rhythms
•  The progression of each year has growing seasons
of plants
o  Tulips are sensitive to light; open during day and close at night
•  Sun’s energy is also cause of weather patterns and
ocean currents
What’s in the Night Sky?
•  What may seem like a jumbled mass of stars can
actually be put together to form constellations
o  Groups of stars organized in a recognizable pattern
•  These are the same patterns that ancient Greek
philosophers looked at
•  By watching the night sky for many years, ancient
Greeks calculated that stars more distant than
planets
o  Telescope invented thousand years later
o  Discovered two more planets: Neptune and Uranus
o  Several other large celestial bodies: Ceres and Pluto
Gravity holds the Solar System Together
•  RECALL – every object in solar system pulls on every
other object
•  Force of gravity depends on…….WHAT???????
o  Their masses and distance between them
•  The sun exerts the largest force in the solar system
because…..?
•  Gravity also keeps moons orbiting around planets
•  Jupiter has gravitational force on use but we don’t
notice it…..why?
A Family of Planets
•  Solar system has objects and own set of rules
•  The solar system is the sun and all of the objects that
orbit it
•  Sun makes up nearly 99% of mass of our solar system
•  Eight planets and their moons make up the
remaining 1%
•  Solar system also contains dwarf planets, asteroids,
comets, dust, and gas
Eight Planets Orbit the Sun
•  Planets can be seen because their surface or
atmosphere reflect sunlight
•  Planet’s distance form sun determine how long it
will take to orbit sun
•  Mercury (closest to sun): 88 days to orbit sun
•  Earth: 365.25 days (reason for leap year)
•  Neptune (farthest): 165 years (60, 225 days)
•  Diameters of large planets (Jupiter, Saturn) only
fraction of the sun
2 5/12/15 Satellites Orbit Objects with Larger Mass
•  Satellite – object in orbit around a body that has a
larger mass
o  Moon is Earth’s satellite
•  First four planets: small, rocky with few or no satellites
o  Mercury (none), Venus (none), Earth, Mars
•  Next four: large, gaseous with many satellites
o  Jupiter, Saturn, Uranus, Neptune
•  We know of 135 satellites in our solar system
Satellites
•  Space missions have discovered many small
satellites
o  More could be found in future
•  Smallest are less than 3 km in diameter
•  Largest moons in our solar system (Jupiter’s
Ganymede and Saturn’s Titan) are larger than
planet Mercury
o  1970: we only knew of 33
The Moon
•  Orbits the sun indirectly
o  Orbits Earth at distance of 384,000 km
•  Surface is covered with craters as a result of smaller
bodies crashing into it
•  Maria, large dark patches on the moon, are areas
of lava that flowed out from interior to fill in craters,
later cooling to solid rock
•  Like the sun, the moon affects life on Earth through
its movements and gravitational influence
Moon has Phases because it Revolves around Earth
•  Phases – moon’s appearance to have different
shapes throughout the month
o  Relative positions of the Earth, moon, and sun determine phases
•  At any given time, sun illuminates half of the moon
o  As moon revolves around Earth, illuminated portion that faces Earth
changes
o  Full moon: half that is lit is facing you
o  New moon: side that is dark is facing you
•  From one full moon to the next = 29.5 days or one
calendar month
o  Many calendars are based on the movement of the moon
Eclipses
•  Eclipse – when Earth, sun, and moon are in a
straight line
o  Occurs when one object moves into the shadow of another object
•  During new moon, moon may cast shadow onto
Earth
•  Solar eclipse – sky turns dark as moon blocks the sun
•  Lunar eclipse – full moon passes in front of Earth’s
shadow during nighttime
3 5/12/15 Moon Affects Earth’s Tides
•  Tides are mainly result of gravitational influence of
the moon
o  Pull is strongest on side nearest to the moon…..why?
•  Water is pulled toward moon, but so is solid earth
o  We notice water movement more because it is liquid
•  Because Earth rotates, one area on Earth will have
two high tides and two low tides in a period of 24 h
50 min
o  These tides change throughout month because moon is orbiting Earth
•  Sun has impact but it is minor
o  When sun is on same side of Earth as moon, g-forces are strongest and
tides are highest for the month
19.2 The Inner and Outer Planets
•  Key Ideas:
o  How are the inner planets similar to one another?
o  What are gas giants?
o  What type of bodies lie beyond the gas giants?
Key Terms
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Terrestrial planet
Hydrosphere
Asteroid
Dwarf planet
Gas giant
The Inner Planets
•  Terrestrial planets – highly dense planets nearest to
the sun: Mercury, Venus, Earth, and Mars
•  These terrestrial planets are relatively small and
have solid, rocky surfaces
•  Planets have similar compositions and share many
similar surface features
o  Metallic cores
o  Rocky surfaces with some of same terrain features as Earth
o  Mountains, canyons, and craters
4 5/12/15 Mercury has Extreme Temperatures
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Mariner 10 – first probe to investigate Mars
Mercury is covered with craters
Never very far from sun, small orbit around the sun
Distances in solar system measured in distance of
Earth to the sun
Mercury
o  1 Astronomical Unit (AU) = 150 million km
•  Mercury is 0.4 AU
o  Surface temp can reach 720 K during day (836 F)
o  Night surface temp can reach 103 K (-274 F)
•  Has almost no atmosphere and no water
•  1 day lasts 59 Earth days
•  I year lasts 88 Earth days
Venus and Greenhouse Effect
•  Venus is 0.7 AU from sun
•  Can be seen near sunrise or sunset
o  Often called morning or evening star
•  Surface has numerous mountains and plains
•  Spins very slow and in opposite direction than most
of other planets and sun
•  1 day is 234 Earth days, 1 year is 225 Earth days
•  Does not provide environment to support life
•  Hot and atmosphere has large amounts of sulfuric
acid
Earth’s Ideal Conditions
•  Only planet we know that sustains life
•  Only planet that has large amounts of liquid water
on its surface
•  Hydrosphere – all the water on Earth’s surface, both
liquid and frozen state
•  Hydrosphere helps moderate temperature of Earth
Venus
•  Atmospheric pressure is 90 times greater than Earth
•  Thick carbon dioxide atmosphere traps sun’s heat
o  Causing runaway greenhouse effect
o  Raises temperature greater than 700 K
Atmosphere Protects Earth
•  Atmosphere = 78% nitrogen, 21% oxygen, 1% argon,
carbon dioxide, other gases
•  Helps moderate temperatures between day and
night
o  Greenhouse effect makes sure that surface does not freeze at night
•  Blocks radiation and high-energy particles from sun
•  Also protects from space debris, man made and
rocks
o  Most burn up when trying to enter, only large ones make it through
•  Early atmosphere contained more carbon dioxide,
methane, and ammonia
o  Microbes changed atmosphere, then later by plants
5 5/12/15 Missions to Mars
•  Viking 1 and Viking 2 landed on surface in 1976
o  2004 – 2 Mars rovers landed on surface
•  Mars has two polar ice caps made up if frozen
carbon dioxide and possibly water
•  Features on the surface suggest water once flowed
on the surface
•  Has very thin atmosphere, mostly carbon dioxide
•  Mars is 1.5 AU
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Has 2 small satellites (Phobos and Deimos)
Mars’ mass is 11% of Earth’s
1 year is 1.9 Earth years, 1 day is 24.7 Earth hours
Temperatures range between 144 K to 300 K
Mars’ Extreme Landform
•  Volcano (Olympus Mons) is tallest mountain in solar
system
o  Almost 3 times height of Mount Everest
o  Mars has no plate tectonics – lava remains in same location and
volcanoes can grow very large
•  Many impact craters
o  Thin atmosphere doesn’t burn up objects
o  Lack of liquid water slows down weathering of craters
•  Surface is red because iron oxide in soil
•  Frequent dust storms stronger than those in Sahara
o  Form large red dunes
Mars
Asteroid Belt
•  Lies between Mars and Jupiter
•  Rocky objects ranging between 3 km and 700 km
o  Asteroids – small solar system bodies
•  Asteroid Ida is 58 km long and large enough to
have captured its own small satellite (Dactyl)
•  Asteroids rarely leave the belt but some wander
away and may enter Earth’s orbit
•  Ceres is largest celestial body in the belt
o  Diameter of 940 km, once considered a planet due to tis size
o  Considered a dwarf planet – celestial body that orbits the sun, round
because its own gravity, but has not cleared its own orbital path
All Gas Giants Have Rings and Satellites
The Gas Giants
•  Gas giants – Jupiter, Saturn, Uranus, Neptune
•  Outer planets are much larger than inner planets
and have thick, gaseous atmospheres, many
satellites, and rings
•  These planets have no solid surface
o  Spacecraft cannot land on them
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Pioneer missions in 1972 and 1973
Voyager 1 and Voyager 2 in 1977
Galileo in 1989
Cassini-Huygens reached Saturn in 2004
•  Saturn rings were discovered in 1659
•  Modern technology discovered thin, faint rings of
other gas giants
o  Uranus’ rings were discovered in 1977
•  Most of known satellites were discovered by space
missions
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Jupiter has more than 60
Saturn has more than 40
Uranus has at least 27
Neptune has at least 13
Most are cratered and some have thin atmospheres
6 5/12/15 Jupiter is Largest Planet
•  1,300 times that of Earth
o  If it were a mere 80 times larger than it currently is, it would be a star
Distance: 5 AU
12 Earth years to orbit sun
1 day is less than 10 Earth hours
Has swirling clouds of hydrogen, helium, methane,
and ammonia
•  Has feature known as Great Red Spot
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o  Giant hurricane twice size of Earth; going on for hundreds of years
•  1610: Galileo discovered Jupiter’s 4 largest satellites
o  Ganymede, Callisto, Io, Europa
o  Io has thin atmosphere and active volcanoes
o  Europa may contain liquid water under its icy surface
Saturn’s Ring System
95 times mass of Earth
Takes more than 29 years to orbit sun
1 day takes 10.7 Earth hours
Rotates fastest at equator
has many satellites and ring system
•  Rings are tiny particles of dust, rock, and ice
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o  Size range from few millimeters to several meters; most are large snowball
•  Competing gravitational forces hold particles in
place
•  Some rings are thin while others are 10 km to 20 km
o  Scientists are unsure why they formed
Saturn
Saturn: Still Forming?
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Radiates 3 times as much radiation as it receives
Helium may be condensing and falling inward
As helium nears the central core, it heats up
Eventually the extra heat is radiated away
When atmospheric helium is used up, it will reach
state of equilibrium
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Discovered in 1846 by Johann Galle
Size is 17 Earth masses
165 years to orbit the sun and is 30 AU
Gas in both planets’ atmosphere is 58 K
1 day on Uranus is about 17.25 hours
Uranus and Neptune: Blue Gas Giants
•  Large planets with thick atmosphere of hydrogen,
helium and methane
o  Methane gives the blue coloring
•  William Herschel discovered Uranus in 1781
o  Name given form mythology
o  Size of 14 Earth masses
o  84 years to orbit sun and is 19 AU
•  Scientists used what they knew about gravity to
guide search for other planets
•  Changes in expected orbit of Uranus could be used
to predict existence and position of other planets
Neptune
o  Pole is tilted at 98 degree angle; most extreme seasons of solar system
o  Few clouds and has wind speeds of 200 to 700 km/h
•  1 day on Neptune = 16 hours
o  Storm systems similar to Jupiter
o  Wind speeds up to 1,100 km/h
7 5/12/15 Beyond Gas Giants
•  Beyond the gas giants are numerous small bodies
•  Composed of ice and rock
•  Until 2006, the word planet never had a clear
scientific definition
•  International Astronomical Union (IAU) defined what
a planet is
o  Pluto was taken off of planet list because it has not cleared its orbital path
o  It is considered a dwarf planet
Objects Beyond Neptune
•  Kuiper Belt is populated by small bodies of ice and
rock, containing Pluto
•  Scientists think these are remnants of material that
formed early solar system
•  Recently, large bodies have been found
o  Called Eris
o  Also a dwarf planet with distance of 90 AU
•  Pluto is 0.002 Earth’s mass, distance is almost 40 AU,
and 1 orbit takes 248 Earth years
19.3 Formation of the Solar System
•  Key Ideas:
•  How did early astronomers understand and
describe the solar system?
•  How did our solar system form?
•  How did Earth’s moon form?
Early Models of the Solar System
•  Early models only included objects in our system
o  Limited technology, only used naked eye
•  Ancient Greeks observed sky to keep track of time
•  They used logic and math, especially geometry
•  Aristotle tried to explain phases of the moon and
eclipses
Early Astronomy
•  Group of stones in Nabta, Egypt may be earliest
record of human interest in astronomy
o  Possibly 6,000 to 7,000 years old
o  Thought to line up with the sun at the summer solstice
•  Stonehenge is thought to be world’s oldest
observatories
Early Models
•  Nicolaus Copernicus realized that the sun was the
center – “heliocentric” in 1543
•  1605 – Johannes Kepler revised Copernicus’ model
•  Proposed orbits are ellipses or ovals
o  We use this model today
o  His model was “geocentric” or earth-centered
•  140 C.E.- Ptolemy added to Aristotle’s model
o  Thought sun, moon, and planets orbited Earth in perfect circles
o  Although incorrect, it helped astronomers predict many astronomical
events for more than 1,000 years
8 5/12/15 Elliptical Orbits
•  Before 1687, paths planets take could be described
but not the reason they stay in orbit
•  Newton explained that gravity kept planets orbiting
the sun and satellites orbiting planets
•  Newton explained that it did not only apply to
planets
•  RECALL – every object exerts force on another
•  Everything in the universe follows same rules and
acts in the same predictable way
•  Ideas are basis for much of astronomy and physics
How Did Solar System Form?
•  Use the age of meteorites to estimate age of solar
system
think it formed 4.6 billions years ago
•  Currently accepted model is the nebular hypothesis
•  Nebula – large cloud of dust and gas in space
•  Hypothesis states that planets formed when small
particles in a nebula collided and stuck together in
a process called accretion
•  Hypothesis also explains:
o  Why terrestrial and gas giants differ in composition
o  Why the orbits of the planets are almost circular
o  Why the planets are almost in the same plane
Nebular Hypothesis
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Nebular Hypothesis
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Nebular Hypothesis
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Other Objects in Solar System
•  Satellites, comets, asteroids, meteoroids
•  Satellites – objects that orbit larger objects
•  Comets – small bodies made of rock, ice, and dust
that move around the sun in very elliptical orbits
•  Asteroids – small rocky objects found mainly
between Mars and Jupiter
•  Meteoroids – smaller pieces of rock that move
through space
9 5/12/15 Why Study Comets?
•  Comets contain dust and ice made from methane,
ammonia, carbon dioxide, and water
•  1994 – comet Shoemaker-Levy hit Jupiter
o  Showed comets also contain silicon, magnesium, and iron
•  Scientists have learned more about materials
making up solar system
•  Comets form tails of gas when passing the sun
o  Some have two tails: one is ion tail made of charged particles that always
points away from sun
o  2nd tail is dust tail that follows comet’s orbit
What Are Meteorites?
•  Rocks and other objects in space frequently enter
Earth’s atmosphere
o  Most burn up
o  Many large rocks form space that survive Earth’s atmosphere come from
asteroids
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Rocks that reach Earth’s surface are called meteorites
Three major types:
Stony – rocky materials, carbon compounds, water
Iron – iron and nickel
Stony-iron – both rocky metallic material
Most known meteorites are stony with similar composition
to Earth and the moon
How Did Moon Form
•  Earth and moon are made of similar but not
identical materials
•  New theory states moon broke off from Earth when
large objet hit Earth about 4.5 billion years ago
o  Much of Earth was molten or melted
•  Scientists think moon formed from Earth’s crust and
mantle, along with iron from object that hit Earth
Where do Comets Come From?
•  As solar system formed, some small planetesimals
did not join others
•  They moved far away from the sun and developed
very long orbital periods
•  These make up the Oort cloud: shaped like a
sphere and may be 100,000 AU wide
•  Planetesimals that stayed in in nebula disk formed
the Kuiper Belt
•  Kuiper Belt located beyond orbit of Neptune
•  Most comets come from this region
Effects of Meteorite Impacts
•  Earth has close to 100 craters larger than 0.1 km in
diameter
•  Barringer Crater in Arizona
o  Meteorite with mass of 200,000 metric tons
o  More than 1 km wide and 175 deep
o  25 metric tons of iron meteorite pieces have been found
•  Many scientists think large asteroid or comet hit
Earth 65 million years ago, killing dinosaurs
•  Impact thought to equal 10 million hydrogen bombs
•  Impact would have thrown dust into atmosphere
o  Made sky dark, killing plants and those that eat them, then meat eaters
had no food
Exoplanets
•  Exoplanet – planetlike object that orbits a star other
than our sun
•  Too faint to see with optical telescopes
•  As exoplanet orbits star, its gravitational force pulls
on the star, causing it to wobble
o  Scientists look for these wobble events
•  Scientists have only found large exoplanets
because they exert larger g-force = bigger wobble
•  Have discovered exoplanets similar in mass to
Jupiter or Saturn
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