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Chapter 23 Key Terms
Solar System
Planet
Geocentric Theory
Heliocentric Theory
Orbit
Ellipse
Dwarf Planet
Terrestrial Planet
Jovian Planet
Asteroid
Comet
Meteor
Meteorite
Moon
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Chapter 23
OUR SOLAR SYSTEM
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The Solar System

Can you name the 8 planets in their order from the sun?

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

New Horizons mission
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Early Theories

Geocentric Theory
 Before
Christ, people believed that the Earth was stationary and
everything in our solar system revolved around the Earth
 Philosophers

such as Plato and Aristotle helped influence this theory
Problems:
 Retrograde
motion – some planets seemed to slow down, stop,
and then back up when compared to the stars
 Planets
sometimes seemed large and close at times, and small
and far away at other times
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Early Theories

Around the 2nd century AD, Ptolemy shifted the planet’s spheres
so Earth was not at its center

Around the 16th century, Nicolaus Copernicus suggested that
the Earth and planets moved around the sun
 His
work, The Revolutions, was published after he died and
suggested his theories

Copernicus’s ideas were soon called the Heliocentric Theory

Copernican Revolution
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Early Theories





Copernicus’s Heliocentric Theory still had a few problems
Several men contributed to his theory
Tycho Brahe: built special instruments and influenced another
scientist (Kepler) to determine the true shape of orbits
Galileo Galilei: Observed moons orbiting Jupiter using his telescope
Johannes Kepler: Successfully described planetary motion
 Formulated
3 laws
 Planets move in ellipses with the sun at the focus
 A planet moves faster when closer to the sun
 The average distance from the sun and the time it takes a planet to orbit
the sun always have the same mathematical relationship
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Early Theories

Keplers 3 laws are very important to astronomers
 Space
engineers rely on these laws to help plan space missions

Aphelion: when a planet is farthest from the sun

Perihelion: when a planet is closest to the sun

No theory provided why a planet followed the elliptical orbit

Isaac Newton
 Developed
a mathematical law to describe gravity
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Planets

2006, the International Astronomical Union (IAU) redefined what
a planet was

A body in the solar system that:
 Orbits
 Has
the sun
a spherical shape
 Does
not share the space of its orbit with any other object of
significant size, other than moons
 According
to this classification, there are only 8 planets
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Planets

Dwarf Planets are objects that:
 Orbit
 Are
rigid and can be nearly spherical
 Can
 Are

the sun
share their orbits with other bodies of similar size
NOT satellites
The main difference between a planet and a dwarf planet is
what is around the dwarf planet
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Planets

Terrestrial Planets
 Planets
similar in size and density to Earth
 Mercury, Venus, Earth, Mars
 Also called the “inner planets”

Jovian Planets
 Planets
larger than Earth and have low densities
 Sometimes called “gas giants” because they are made mainly of
elements that are gases here on Earth

Jovian planets have greater surface gravity because of their size
and mass
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Planets

Inferior Planets
 Planets

that orbit closer to the sun than Earth
 Can
only be seen near sunrise or sunset
 Can
cross in front of the sun - transit
Superior Planets
 Planets
farther from the sun than the Earth
 Retrograde
motion
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Planets

Mercury
 Smallest
planet
 Temperatures on the day side can reach 800oF, while temps on
the night side can plunge to -300oF
 No moons

Venus
 Opaque
atmosphere
 Tilted 177o on its axis
 Highest surface temperature of any planet: 860oF
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Planets

Earth
 3rd
planet from the sun
 The

most dense planet in the solar system
Mars
 Very
 Has
thin atmosphere
2 very small moons
 Contains
the largest volcano in the
solar system (Olympus Mons)
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Planets

Jupiter
 The
largest planet in the solar system
 The
bands are made of ammonia compounds that move around
the planet
 The
great red spot is actually a huge storm
 Jupiter
has many moons, but the 4 largest are the most well
known: Io, Europa, Callisto, and Ganymede
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Planets

Saturn
 2nd
largest planet
 Composition
is so light, it would float in water
 Has
an extensive ring system
 Has
62 moons, the largest is Titan
 Has
a large seasonal storm called the
Great White Spot
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Planets

Uranus
 Known
for its axial tilt – 97.8o
 27 known moons
 13 known rings
 Has the blue color because of the light reflecting off the water
molecules

Neptune
 Farthest
planet from the sun
 13 moons, but only 2 are observable from Earth
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Dwarf Planets



Orbit the sun, spherical shape, and can share their orbit with other
objects of similar size
Pluto was discovered in 1929 by Clyde Tombaugh
Pluto has many unique characteristics
 Orbital
plane is tilted more than 17o to the ecliptic plane
 Its orbit is more elliptical than any planet
 Its perihelion is closer to the sun than Neptune’s perihelion
 Its density is much less than the terrestrial planets, but it is believed to
be mostly rock and ice
 Forms a binary planet with its moon, Charon
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Dwarf Planets

The discovery of Eris is what spurred the change in definition
 Eris

is almost twice as far from the sun as Neptune
There are 5 known dwarf planets
 Pluto,
Eris, Haumea, Makemake, Ceres
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Small Solar System Bodies

Asteroids
 The
largest of the small solar system bodies
 Size can range from a house to 1/3 of the moon
 Cannot hold an atmosphere because of their weak gravity
 Can be oddly shaped


Most asteroids have orbits in the asteroid belt (between Mars and
Jupiter)
Two large asteroid families lie in the same orbit as Jupiter
 Trojans
 Greeks
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Small Solar System Bodies

Comets
 Small
solar system body made of rock and ice that orbits the sun
 May be chunks of frozen gas covered in gravel and dust

Two parts to the comet: head and tail


Two sections to the head

Nucleus: solid part

Coma: gaseous envelope that surrounds
the nucleus
The tail only forms when the comet enters
the inner solar system because of light pressure
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Small Solar System Bodies

Meteoroids
 Meteoroids
are exactly like asteroids, except in size
 Asteroids
can be seen from Earth with a telescope, whereas
meteoroids cannot

Meteors
A
meteoroid that enters Earth’s atmosphere
 Friction from the air causes it to heat up and glow

Meteorites
 Meteors
that reach the surface
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
Psalm 19:1

The heavens declare the
glory of God; and the
firmament sheweth his
handywork.