Astronomy

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Previous Lessons
Open Chapter Ch. 1: A Modern View of the Universe
Lesson #1 The Scale of the Universe
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Lesson #2 The History of the Universe
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Lesson #3 Spaceship Earth
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Open Chapter Ch. 2: Discovering the Universe for Yourself
Lesson #4 Patterns in the Night Sky
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Lesson #5 The Reason for Seasons
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Lesson #6 The Moon, our Constant Companion
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Lesson #7 Ancient Mystery of the Planets
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Open Chapter Ch. 3: The Science of Astronomy
Lesson #8 The Ancient Roots of Science
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Lesson #9 Ancient Greek Science
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Lesson #10 The Copernican Revolution
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Lesson #11 The Nature of Science
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Open Chapter Ch. 4: Understanding Motion, Energy, and Gravity
Lesson #12 Describing Motion
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Lesson #13 Newton's Laws of Motion
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Lesson #14 Conservation Laws in Astronomy
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Lesson #15 The Force of Gravity
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Open Chapter Ch. 5: Light: The Cosmic Messenger
Lesson #16 Basic Properties of Light and Matter
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Lesson #17 Learning from Light
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Lesson #18 Collecting Light with Telescopes
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Exam Exam 1
Open Chapter Ch. 6: Formation of the Solar System
Lesson #19 A Brief Tour of the Solar System
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Lesson #20 The Nebular Theory of Solar System Formation
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Lesson #21 Explaining the Major Features of the Solar System
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Lesson #22 The Age of the Solar System
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Open Chapter Ch. 7: Earth and the Terrestrial Worlds
Lesson #23 Earth as a Planet
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Lesson #24 The Moon and Mercury: Geologically Dead
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Lesson #25 Mars, a Victim of Planetary Freeze Drying
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Lesson #26 Venus, a Hothouse World
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Lesson #27 Earth as a living planet
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Open Chapter Ch. 8: Jovian Planet Systems
Lesson #28 A Different Kind of Planet
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Lesson #29 A Wealth of Worlds: Satellites of Ice and Rock
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Open Chapter Ch. 9: Asteroids, Comets, and Dwarf Planets
Lesson #30 Classifying Small Bodies
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Lesson #31 Asteroids
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Lesson #32 Comets
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Lesson #33 Pluto and the Kuiper Belt
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Lesson #34 Cosmic Collisions - Small Bodies vs Planets
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Open Chapter Ch. 10: Other Planetary Systems
Lesson #35 Detecting Planets Around Other Stars
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Lesson #36 The Nature of Planets Around Other Stars
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Lesson #37 The Formation of Other Planetary Systems
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Exam Midterm Exam
Open Chapter Ch. 11: Our Star
Lesson #38 The Sun, Our Star
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Lesson #39 Nuclear Fusion in the Sun
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Lesson #40 Sun-Earth Connection
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Open Chapter Ch. 12: Surveying the Stars
Lesson #41 Properties of Stars
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Lesson #42 Patterns in the Stars
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Lesson #43 Star Clusters
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Open Chapter Ch. 13: Star Stuff
Lesson #44 Star Birth
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Lesson #45 Life as a Low Mass Star
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Lesson #46 Life as a High Mass Star
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Open Chapter Ch. 14: The Bizarre Stellar Graveyard
Lesson #47 White Dwarfs
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Lesson #48 Neutron Stars
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Lesson #49 Black Holes: Gravity’s Ultimate Victory
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Exam Exam 3
Open Chapter Ch. 15: Our Galaxy
Lesson #50 The Milky Way Revealed
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Lesson #51 Galactic Recycling
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Lesson #52 The History of the Milky Way
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Open Chapter Ch. 16: A Universe of Galaxies
Lesson #53 Islands of Stars
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Lesson #54 Distances of Galaxies
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Lesson #55 Galaxy Evolution
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Lesson #56 The Role of Supermassive Black Holes
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Open Chapter Ch. 17: The Birth of the Universe
Lesson #57 The Big Bang Theory
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Lesson #58 Evidence for the Big Bang
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Lesson #59 The Big Bang and Inflation
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Open Chapter Ch. 18: Dark Matter, Dark Energy, and the Fate of the Universe
Lesson #60 Unseen Influences in the Cosmos
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Lesson #61 Structure Formation
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Open Chapter Ch. 19: Life in the Universe
Lesson #62 Life on Earth
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Lesson #63 Life in the Solar System
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Lesson #64 The Search for Extraterrestrial Intelligence
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Lesson #65 Interstellar Travel and Implications for Civilizations
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Exam Final Exam

Assignments:

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Lesson Objectives:

- Newton's impact on astronomy
- Three laws of motion



How did Isaac Newton change our views on the universe? In a famous story, he observed an apple falling from a tree and realized that the same gravity pulling the apple down to the ground was also keeping the Moon orbiting the Earth. One of Aristotle's key ideas to support the idea of an Earth-centered universe had been that the heavens were separate from the Earth and that physical laws on Earth did not apply to the heavens.

Isaac Newton's discovery of gravity dismantled that. Since gravity applied to both the Earth and the heavenly bodies, they were clearly together in one universe. As a result of Newton's discoveries, people began to apply the same physical laws in effect on Earth to how objects operate in the heavens or cosmos.

In later years, this became its own field of study known as astrophysics. Astrophysics deals with the application of physical laws discovered on Earth to phenomena throughout the universe.



Isaac Newton defined three laws that apply to all motion, whether it be on Earth or the movement of a distant planet, star, or galaxy.

The first law states that an object moves at a constant velocity if there is no net force acting on it. This is why when you are traveling on a plane at cruising altitude, you can walk around and do other activities without feeling any different from being on the ground. While the plane is moving at a constant velocity, there is no net force acting on you. When the plane speeds up, slows down, or turns, however, this change in velocity results in a net force on your body. Note that this net force is experienced only as long as the plane is accelerating, or changing velocity.



Newton's second law offers a quantitative relationship. Force = mass times acceleration or (F = ma). This tells us what happens if there is a net force. A good example of this is how you can throw a baseball much farther than you can throw a shot in the shot put.

The shot has significantly greater mass than the baseball so it takes a much greater force to create the same acceleration.



The third law states that for any force, there is an equal and opposite force.

For example, when you are standing on the ground, your weight exerts a downward force. If this were the only force being applied to your body, Newton's first law would indicate that you should accelerate downward. The fact that you are not moving downward points to the fact that the ground is pushing up on you with the same force that your weight is pushing down. This is an example of Newton's third law of motion - for every force, there is an equal and opposite reaction force.

This also explains how a rocket works. A rocket engine generates a force that drives hot gas out the back, which creates an equal and opposite force that propels the rocket forward.