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:

- The planets
- Apparent retrograde motion
- Stellar parallax



5 planets are easy to find with the naked eye - Mercury, Venus, Mars, Jupiter and Saturn. Mercury is rarely visible since it is so close to the Sun, but you can occasionally catch a glimpse of it just after sunset or just before sunrise. If you see a bright 'star' in the early evening or early morning, it is probably Venus. Jupiter, when visible, is the brightest object in the sky besides the Moon and Venus. Mars can be recognized by its reddish color. Saturn, while highly visible, can look similar to other stars so it can be helpful to use a star chart to identify it.

Something that can also help you to identify planets is the fact that planets do not twinkle as much as stars.



For thousands of years, ancient peoples believed in an Earth-centered universe, but as they observed the planets that were visible to the naked eye, there was one particular mystery that they had difficulty explaining.

The stars, the Sun, and the Moon always appear to rise in the east and set in the west, due to Earth's rotation. Planets, however, during the course of the year, will sometimes reverse direction and go westward instead of eastward, in what is referred to as apparent retrograde motion.

If you look at the diagram on the right, you can see what causes this. If you visualize yourself as the green dot walking quickly around the Sun and a friend as the red dot walking more slowly, there is a point where your friend will appear to move backwards - when you catch up to and pass her.

This is a simple concept to explain if you know that the Earth orbits around the Sun, but since the ancient Greeks believed in an Earth-centered universe, they were forced to come up with some very complex explanations for apparent retrograde motion.



Stellar Parallax occurs where a star appears to shift in position when we see it from different points in Earth's orbit.

Stellar parallaxes are not detectable to the naked eye because stars are so far away, and even with the most powerful telescopes, parallax can only be measured for the nearest stars. A star's parallax can be used to calculate its distance from Earth using trigonometry.

The ancient Greeks rejected the idea of stellar parallax because they assumed the Earth was stationary at the center of the universe, and also because they did not believe the universe could be big enough for parallax to be undetectable to the naked eye. However, the invention of powerful telescopes later proved that the Universe is so much bigger than our solar system and galaxy alone.