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Section 1: Sun, Earth, and Moon
Section 2: The Inner and Outer
Planets
Section 3: Formation of the Solar
System
Key Terms
Planet
Solar System
Satellite
Phase
Eclipse
The View from Earth
If you observe stars on a clear night you
may notice that one of the brighter
objects changing position and crossing
the path of stars. These are planets
coming from the Greek word meaning
wanderers.
A planet is any of the nine primary bodies
that orbit the sun: a similar body that
orbits another star
There are five planets that are visible to the
unaided eye: Mercury, Venus, Mars, Jupiter, and
Saturn.
The sun is our closest star
There are billions of stars but the sun is our most
important star.
Why can’t we see other star during the day?
Because the sun makes the daytime sky to bright
The sun is an average star of size and
temperature
Compared to the Earth the sun is 1.4 million
km in diameter, about 110 times the
diameter of Earth and has a mass 300,000
times the mass of Earth
The solar system is the sun, planets, and other
objects that orbit the sun. This includes
objects of all sizes (large planets, small
satellites, asteroids, comets, gas and dust).
Everything revolves around the sun
The sun is not just the object that all planets
orbit, it is also the source of heat and light
for the entire system.
Many patterns of human life depend on the
sun’s cycle.
Heat from the sun is a main cause of weather
patterns on Earth. Another type of weather,
space weather, is caused by energetic
particles that leave the sun during solar
flares and storms.
What can happen during a solar flare?
Can zap communication satellites and cause
blackouts.
Planets and distance stars are visible in the night
sky
When we pick out the shapes of constellations, we
use some of the same patterns the Greeks saw
and named. The constellations reminded the
Greeks of there myths.
By watching the sky for many years , the
ancient Greeks calculated that the stars
were more distant than the planets were.
With the invention of the telescope, people
found other objects in the night sky,
including many faint stars and three more
planets: Uranus, Neptune, and Pluto
Earth is a part of a solar system
The solar system is the sun and all of the
objects that orbit it.
The sun is the most important part of our solar
system and makes up 99% of the total mass
of the solar system and the nine planets
make up the last 1%.
Gravity holds the solar system together
The force of gravity between two objects
depends upon their masses and the distance
between them.
The sun exerts the largest force in the solar
system because its mass is so large.
What would happen with out the sun’s pull?
The planets would fly off into space
Gravity is also the force that keeps moons
orbiting around planets.
Nine planets orbit the sun
Why can planets be seen?
Because their surface or atmospheres reflect
sunlight
A planet’s distance from the sun determines
how long the planet takes to orbit the sun.
Mercury, the closest, takes 88 days to orbit the
sun, which is the shortest time of all the
planets. Earth takes 365.25 days and Pluto,
the most distant planet, takes 248 years or
over 90,000 days.
A satellite is an object in orbit around a body
that has a larger mass. This is why the moon
is a satellite to the planet it orbits.
Satellites orbit planets
All of the planets in our solar system have
moons except Mercury and Venus.
Currently, we know of 102 natural satellites, or
moons, orbiting the planets in our solar
system. Thirty-five years ago we only knew
of 33.
What are the two largest satellites?
Jupiter’s Ganymede and Saturn’s Titan. They
are larger than the planet Mercury.
The Moon
The moon’s surface is covered with craters,
mostly caused by asteroid collisions early in
the history of the solar system.
A maria, or large, dark patches on the moon,
are seas of lava that flowed out of the
moon’s interior and cooled to solid rock.
The moon has phases because it orbits Earth
Throughout the month the moon has different
shapes called phases. The relative position
of Earth, the moon, and the sun determine
the phases of the moon.
There are eight phases of the moon
1. New moon
2. Waxing crescent
3. First quarter
4. Waxing gibbous
5. Full moon
6. Waning gibbous
7. Third quarter
8. Waning crescent
The time form one full moon to the next is
29.5 days, or about one calendar month.
Phases of the moon are not caused by Earth’s
shadow
Earth and the moon may seem to make
shadows that fall on each other all the time.
But Earth, which has a diameter that is four
times the diameter of the moon is a distance
of 30 Earth-diameters from the moon.
Because of this even when the Earth, the moon,
and the sun are lined up only a small part of the
shadow hits Earth.
Eclipses occur when Earth, the moon, and the sun
line up
Eclipse is an event in which the shadow of one
celestial body falls on another.
Eclipse can be predicted and can happen when
Earth, the sun, and the moon are in a straight
line
During a new moon, the moon may cast a shadow
onto Earth. This is a solar eclipse.
When the moon is full, it may pass into the shadow
on Earth and this a lunar eclipse
Because the moon’s orbit is slightly tilted
compared with Earth’s orbit around the sun, the
moon is usually slightly above or below the line
between Earth and the sun. So, Eclipses are
relatively rare.
The moon affects Earth’s tides
Coastal areas on Earth have two high tides and
two low tides each day. Tides are mainly a
result of the gravitational influence of the
moon.
The side of the Earth closest to the moon
experiences the strongest gravitational pull.
This pull creates a bulge.
Because the moon is orbiting Earth as it rotates
the times of the tides change throughout the
month.
When the sun is on the same side of Earth as
the moon, the gravitational forces are at
their strongest, and tides are at their highest
for the month.
Key Terms
Terrestrial Planets
Hydrosphere
Asteroid
Gas Giant
Mercury
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Best time to see is just before sunrise or just
after sunset
Covered with craters
0.4 AU from the sun
670K (melt tin) side closest to the sun and 103K
side away from the sun. Well below the freezing
point of water.
1 day on Mercury equals 58 Earth days
1 year on Mercury is .24 years on Earth
No Atmosphere or Water
Venus
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Only seen near sunset or sunrise. Called either the
morning star or evening star
0.7 AU from the sun
Thick layers of clouds made from carbon dioxide
Surface has mountains and plains
Spins in the opposite direction of the other planets
and sun
1 day on Venus equals 243 Earth days
1 year on Venus is .6 years on Earth
Large amounts of sulfuric acid in atmosphere
Thick clouds cause a greenhouse affect with
temperatures of 700K
Earth
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We measure other planets in relation to Earth
1.0 AU from the sun
Only planet known to sustain life
Contains large amounts of liquid water
All water on Earth’s surface both liquid and frozen
is called the hydrosphere
The hydrosphere moderates the temperature on
Earth
Atmosphere is composed of 78% Nitrogen, 21%
Oxygen, 1% Carbon dioxide and other gases
Atmosphere also moderates temperatures and
protects us from some harmful ultraviolet radiation
and space debris
Mars
 Polar ice cap composed of carbon dioxide and small
amounts of water
 Thin atmosphere composed of carbon dioxide
 1.5 AU from the sun
 Two small satellites Phobos and Deimos
 10% of Earth’s mass
 1 day on Mars equals 24.6 Earth hours
 1 year on Mars is 1.9 Earth years
 Very cold 144K to 300K
 Largest volcanoes in solar system Martian
volcanoes. Olympus Mons largest mountain in solar
system
 Looks red because of Iron oxide
 Large dust storm on the surface
Terrestrial planets are the highly dense planets
near the sun. They are small and have solid
rocky surfaces.
Astronomical Unit (AU) is the distance from the
Earth to the sun.
1 AU equals 150 million km
Mercury
 Venus
 Earth
 Mars
 Jupiter
 Saturn
 Uranus
 Neptune
 Pluto
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= 0.4
= 0.7
= 1.0
= 1.5
= 5.2
= 9.6
= 19.2
= 30.0
= 39.0
The surface temperature of Venus is hotter than
Mercury’s surface because of the amount of
atmosphere which cause a greenhouse effect.
Mercury does not have an atmosphere to trap
the radiation from the sun. This causes the
temperature on Mercury to vary during the day
and at night.
However on Venus, the atmosphere is so thick that
it causes what is known as the runaway
greenhouse effect. This means that the more
heat is built up the more efficient the
atmosphere becomes at trapping radiation.
Olympus Mons is part of the Martian volcanoes.
It is the largest mountain in our solar system.
It is three times the height of Mount Everest.
The Martian volcanoes grew from lava flows.
Because Mars has low gravity, the weight or
the lava is lower than on other planet,
volcanoes could grow very large.
Asteroid Belt
Between Mars and Jupiter lies hundreds of
small rocky objects that range in diameter
from 3km to 700 km. They are called
asteroids. When they enter the Earth’s
atmosphere and burn up they are called
meteors. If they hit the Earth’s surface
which is very rare, they are called
meteorites.
Jupiter
 Largest planet in the solar system
 Large enough to hold 1300 Earths
 80 time more massive could be a star
 5.0AU from the sun
 Takes 12 Earth years to orbit the sun
 Rotates once around its axis in less than 10 hrs
 Atmosphere contains hydrogen, helium, methane, and
ammonia
 Appears to have jet streams and huge storms
 Great Red Spot huge hurricane that is over twice the diameter
of Earth
 Has 39 satellites
 Four largest satellites are Io, Europe, Ganymede, and Callisto
 Io has a thin atmosphere and active volcanoes
 Europe may have liquid water under its icy surface
Saturn
95 times the mass of Earth
 29 years to orbit the sun and rotates on its
axis every 10.7 hours
 Has a system of rings made of dust, rock, and
ice
 Has 30 satellites
 May still be forming
 Radiates three times more energy than it
receives from the sun
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Uranus
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Bluish in color because of the methane
Atmosphere composed of hydrogen, helium, and
methane
Discovered by accident
14 times the mass of Earth
19.2 AU from the sun and takes 84 years to orbit
the sun
Rotates every 17 hours but on its side (98)
Has the most extreme seasons with wind speeds
of 200-500km/h
Neptune
Bluish in color because of the methane
 Atmosphere composed of hydrogen, helium,
and methane
 Discovered after Uranus by Johann Galle
 17 times the mass of Earth
 30 AU from the sun and takes 164 years to
orbit the sun
 Rotates every 16 hours
 Has a storm system similar to Jupiter
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Pluto
Has one satellite Charon
 Thin gaseous atmosphere with a solid icy
surface
 Orbits the sun in a long ellipse
 Averages distance from the sun is 40AU
 Take 248 years to orbit the sun
 Is .002 the mass of Earth
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The outer planets are much larger than the inner
planets and have thick gaseous atmospheres,
many satellites and rings. They are known as
the gas giants
Space missions to outer planets include
Pioneer launched in 1972 and 1973
 Voyager 1 and 2 launched in 1977
 Galileo spacecraft launched in 1989. Flew to
the large outer planets and dropped a probe
into Jupiter’s atmosphere in 1995
 New Horizon is planned to investigate Pluto
before 2020
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Scientist believe that the rings around Saturn may
have formed two different ways. The way is by
a smashed satellite. The second way that the
rings may have formed is by leftover material
when Saturn and its satellites formed.
Scientist believe that helium in Saturn’s outer
layer is condensing and falling inward. As the
helium nears the central core it heats up. When
Saturn uses up its helium, this process will stop
and Saturn will reach a state of equilibrium
Key Terms
Nebula
Nebular Model
Accretion
Comet
Astronomy - The Original Science
Ptolemy expanded on the geocentric “Earthcentered” model of Aristotle. He thought that
the sun, moon, and planets orbited Earth in
perfect circles. His theory described what we
see in day-to-day life, including motions of the
sun and planets. His model was used for over a
thousand years.
Copernicus proposed a heliocentric “sun-centered”
model of the solar system. Where Earth and the
other planets orbited the sun in perfect circles.
Kepler improved on Copernicus model by
proposing that the orbit of the planets
around the sun are ellipses, or ovals, rather
than circles.
Newton explained that the forces that keeps
the planets in orbit around the sun and
satellites in orbit around planets is gravity.
His theory also stated that every object in
the universe exerts a gravitational force on
every other object.
The Nebular Model
According to dating rocks, scientist believe the
solar system is approximately 4.6 billion years
old.
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Why are planets so far away from each other?
Why are they almost in the same plane?
Why are their orbits nearly circular?
Why do they orbit in the same direction?
Why are the terrestrial planets different from
the gas giants?
A nebula is a large cloud of dust and gas in
space
The most widely accepted model of the
formation of the solar system is the nebular
model. According to the nebular model, the
sun, like every star formed from a cloud of
gas and dust that collapsed because of
gravity.
The planets formed by the accretion of matter
in the disk.
The nebular theory explains why terrestrial
planets are different from the gas giants. It
also explains smaller rocks in space.
Rocks in Space
Asteroids can be found between Mars and
Jupiter. Meteoroids are small pieces of rock
that enter Earth’s atmosphere. Most
meteoroids burn up in the atmosphere, and
we see them as meteors streaking through
the night sky. If a meteoroids survive the
atmosphere and hit the ground, it is called a
meteorite.
A comet is a small body of ice, rock, and cosmic
dust loosely packed together that follows an
elliptical orbit that gives off gas and dust in the
form of a tail as it passes close to the sun.
By studying comets, scientist have gained
important information about the material that
made the solar system.
Comets come from the Kuiper belt, a disk-shaped
region beyond the orbit of Neptune, and the
Oort cloud, a spherical region in the outer solar
system beyond the orbit of Pluto.
Halley’s comet is one of the most famous comets.
it appears in Earth’s sky once every 76 years.
Asteroids can be made of many different
elements. There are three major types of
asteroids.
1.
2.
3.
Stony meteorites include carbon-rich
specimens that contain organic material and
water.
Metallic meteorites are made of iron and
nickel.
Stony-iron meteorites are a combination of the
two types.
Most meteorites that have been collected are stony and
have compositions like those of the inner planets and
the moon.
How the Moon Formed
There are several theories for how the moon formed.
Some Thought a separate body was captured by
Earth’s gravity. Others thought the moon formed at
the same time as Earth.
When Earth was still forming it was molten, or heated
to an almost liquid state. A Mar-sized body struck
Earth at an angle and was deflected. At impact, a
large part of the Earth’s mantle was blasted into
space.
Other Stars Have Planets
Astronomers have discovered over 90 planets
by measuring the small gravitational effects
they have on their parent stars. As a planet
orbits its star, it cause the star to wobble
back and forth.