Transcript 7.4 Meet Your Solar System (Pages 291-296)
7.4 Meet Your Solar System (Pages 291-296)
Homework: Page 296 # 1-3, 6, 7 Key Concepts: (Page 296)
• Two
models
of the solar system are the
geocentric
model and
heliocentric
model.
• The planets share many
similar
characteristics, but they also have many differences.
• The
inner
, or terrestrial, planets are
rocky small.
The
oute
and r planets, or gas giants, are
made
of gases and are huge.
• The astronomical unit is defined as the
average
distance
between
Earth and the Sun.
7.4 Meet Your Solar System
(Page 291) A
solar system
is a group of planets that circle one or more stars.
A
planet
is an object that orbits one or more stars (and is not a star itself), is spherical, and does not share its orbit with another object.
The current
heliocentric
(Sun-centered) model of the solar system was first introduced in the 1500s by Polish astronomer
Nicolaus Copernicus
. Previous models of the solar system were
geocentric
(Earth-centered), originating with the Greek astronomer
Ptolemy
.
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Planetary Motion
(Page 292) When we observe planets in the night sky, Venus and Mercury stay near the Sun and can thus only be seen in the early evening or morning. Mars, Jupiter, and Saturn usually appear to move westward as Earth rotates but at times seem to “wander” westward in a slow looping motion. This unusual movement from east to west is called
retrograde motion
.
Retrograde motion
is caused by Earth catching up to and then passing an outer planet in its orbit. Earth is on an inside track and thus moves faster than the outer planets.
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Reviewing Retrograde Motion
Click the “Start” button to review retrograde motion.
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Distances Between Planets
(Page 293) The distances between planets are so large that units such as kilometres cannot represent them in a meaningful way. For this reason, astronomers created a unit for measuring distances in the solar system: the
astronomical unit
(
AU
). One
AU
is approximately equal to the distance between Earth and the Sun, about 150 million kilometres. Earth is
1 AU
from the Sun.
The average distance between the Sun and an object orbiting the Sun is called the object’s
orbital radius
. The orbital radius is expressed in astronomical units.
Copyright © 2010 McGraw-Hill Ryerson Ltd.
Mercury
,
Venus
,
Earth
, and
Mars
are called the
inner planets
. These planets are also called the
terrestrial
(Earth-like) planets. They are relatively small and have solid cores and rocky crusts.
Classification of the Planets
Mercury Venus Earth Mars
(Pages 294-5)
Saturn
,
Jupiter
,
Uranus
, and
Neptune
are called the
outer planets
or the
gas giants
. These planets were formed from large clumps of gas, ice, and dust.
Jupiter Saturn
They are also known for their large gaseous bands and cold temperatures.
Uranus Neptune
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Solar System Data
Inner Planet Data
(Pages 294-5)
Outer Planet Data
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Reviewing The Planets of the Solar System
Click the “Start” button to review characteristics of the planets of the solar system.
Copyright © 2010 McGraw-Hill Ryerson Ltd.