1. 7.4 Meet Your Solar System (Pages 291-296)
Homework: Page 296 # 1-3, 6, 7 Key Concepts: (Page 296)

2. 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 and small. The outer 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.

3. 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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4. 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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5. Reviewing Retrograde Motion
Click the “Start” button to review retrograde motion.
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6. 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.

7. Classification of the Planets
(Pages 294-5)
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.
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. They are also known for their large gaseous bands and cold temperatures.
Mercury
Jupiter
Venus
Saturn
Earth
Uranus
Neptune
Mars
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8. Solar System Data Inner Planet Data Outer Planet Data (Pages 294-5)
Copyright © 2010 McGraw-Hill Ryerson Ltd.

9. 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.