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Astronomy Chapter 2
The Solar System
Observing the Solar System
Section 1
Vocabulary
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Geocentric: A description of the solar system in
which all of the planets revolve around Earth
Ellipse: An elongated circle, or oval shape; the
shape of the planets’ orbits
Heliocentric: A description of the solar system in
which all of the planets revolve around the sun
Intertia: the tendency of a moving object to
continue in a straight line or a stationary object
to remain in place
Main Ideas
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Ptolemy thought that Earth is at the center of the
system of planets
Copernicus thought that the sun is at the center
of the planets. Galileo’s observations supported
Copernicus’s theory.
Kepler discovered that the orbits of the planets
are ellipses
Newton concluded that two factors—inertia and
gravity—combine to keep the planets in orbit
Guiding Questions
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How is Copernicus’s description of the system of
planets different from Ptolemy’s description?
How did Galileo’s observations of Jupiter’s
moons help to show that the geocentric
explanation is incorrect?
What shape are the orbits of the planets? How
was the discovery of this orbit shape made?
What two factors act together to keep the
planets in orbit around the sun?
The Sun
Section 2
Vocabulary
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Nuclear fusion: the process by which hydrogen
atoms join together to form helium, releasing
energy
Core: the central part of the sun, where nuclear
fusion occurs
Photosphere: the inner layer of he sun’s
atmosphere
Chromosphere: the middle layer of the sun’s
atmosphere
Corona: the outer layer of the sun’s atmosphere
Vocabulary
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Solar wind: a stream of electrically charged
particles produced by the sun’s corona
Sunspot: A dark area of gas on the sun that is
cooler than surrounding gases
Prominence: a loop of gas that protrudes from
the sun’s surface, linking parts of sunspot
regions
Solar flare: an explosion of hydrogen gas from
the sun’s surface that occurs when lops in
sunspot regions suddenly connect
Main Ideas
The sun’s energy comes from nuclear
fusion
 The sun’s atmosphere has three layers:
the photosphere, the chromosphere, and
the corona
 Features on or above the sun’s surface
include sunspots, prominences, and solar
flares
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Guiding Questions
How is energy produced in the sun’s core?
 Name the layers of the sun’s atmosphere.
 What is the solar wind?
 Describe three features found on or above
the surface of the sun.
 Why do sunspots look darker than the rest
of the sun’s photosphere?
 How does the number of sunspots change
over time?
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The Inner Planets
Section 3
Vocabulary
Terrestrial planets: the name given to the
four inner planets, Mercury, Venus, Earth,
and Mars
 Retrograde rotation: The spinning motion
of a planet from east to west, opposite to
the rotation of most planets and moons
 Greenhouse effect: the trapping of heat by
a planet’s atmosphere
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Main Ideas
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The four inner planets—Mercury, Venus,
Earth, and Mars—are small and have
rocky surfaces. They are often called the
terrestrial planets
Guiding Questions
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What features do all of the inner planets have in
common?
What is Mercury’s atmosphere like? Explain
Why can astronomers see the surface of Mars
clearly, but not the surface of Venus?
How have astronomers been able to study the
surface of Venus?
What evidence do astrnomomers have that
water once flowed on Mars?
The Outer Planets
Section 4
Vocabulary
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Gas Giant: the name given to the first four
outer planets: Jupiter, Saturn, Uranus, and
Neptune
Main Ideas
Four outer planets—Jupiter, Saturn,
Uranus, and Neptune—are much larger
than Earth
 Pluto and Charon have solid surfaces and
masses much less than that of Earth
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Guiding Questions
How are the gas giants similar to each
other? How are they different?
 How is Pluto different from the gas giants?
 What is the most prominent feature of
Jupiter’s surface? What cuases this
feature?
 Why do astrnomoers think Uranus may
have been hit by another object billions of
years ago?
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Comets, Asteroids, and Meteors
Section 5
Vocabulary
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Comet a ball of ice and dust whose orbit is a long narrow
ellipse
Asteroid: objects revolving around the sun that are too
small and too numerous to be considered planets
Asteroid belt: the region of the solar system between the
orbits of Mars and Jupiter, where many asteroids are
found
Meteoroid: a chunk of rock or dust in space
Meteor: a streak of light in the sky produced by the
burning of a meteoroid in Earth’s atmosphere
Meteorites: a meteoroid that has hit Earth’s surface
Main Ideas
Comets are chunks of ice and dust that
usually have long, elliptical orbits
 Most asteroids revolve around the sun
between the orbits of Mars and Jupiter
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Guiding Questions
What is a comet made of?
 Where are most asteroids found?
 What are the main sources of meteoroids?
 What is the difference between a meteor
and a meteorite?
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Is There Life Beyond Earth?
Section 6
Vocabluarly
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Extraterrestrial Life: life that arises outside
of Earth
Main Ideas
Earth has liquid water and a suitable
temperature range and atmosphere for
living things to survive.
 Since life as we know it requires water,
scientists hypothesize that mars may have
once had the conditions for life to exist
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Guiding Questions
What conditions does life on Earth need to
survive?
 Why do astronomers think there could be
life on Europa?
 How did the Viking missions search fro life
on Mars?
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