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:

- Venus's surface
- Geological activity
- Venus's atmosphere



Venus' thick cloud cover makes it hard to see to the surface. However, Venus shows features of volcanoes and tectonics similar to Earth. Venus lacks erosion because it is too hot for any type of rain or snow. Also Venus has virtually no wind or weather because of its slow rotation.

Venus lacks plate tectonics, which are important for shaping most of Earth's major geological features such as mountain ranges and ocean trenches. This is a mystery to scientists as Venus has a thick, strong lithosphere. However, scientists have guessed that Venus' lithosphere is stronger than the Earth's and thus resistant to breaking into plates.



Internal heat on Venus should be similar to the Earth due to their similar sizes, which should lead to similar levels of geological activity.

In fact, there are relatively few impact craters meaning the surface is geologically young.

Furthermore, Venus's clouds contain sulfuric acid, which comes from volcanic outgassing. Over time, sulfur dioxide disappears from the air, so its presence means outgassing had to have happened less than 100 million years ago.

However, there is little evidence of erosion on Venus because it is too hot for rain and the planet rotates extremely slowly (once every 243 days), so there is no wind or weather.

One mystery of Venus is an apparent lack of plate tectonics. On Earth, stresses caused by convection currents in the mantle fractured our lithosphere into tectonic plates. The movements of these tectonic plates are responsible for shaping most of Earth's major geological features such as mountain ranges and ocean trenches, and also means that different regions of the Earth have different geological features and different ages.

On Venus, on the other hand, the entire planet looks to have aged uniformly. Scientists hypothesize that Venus has a thicker and stronger lithosphere than the Earth, so it has resisted fracturing caused by mantle convection.



Venus is a lot closer to the Sun, but the density of its clouds means its surface actually absorbs less sunlight than Earth. If it weren't for the greenhouse effect caused by a carbon-dioxide heavy atmosphere, it would actually be colder than Earth.

Why are the Earth's atmosphere and Venus's atmosphere so different?

Earth and Venus both experienced the same volcanic outgassing which released massive amounts of water vapor and carbon dioxide into the air. Water vapor and carbon dioxide, as you may recall, both function as greenhouse gases. The difference is, our water vapor condensed into rain and formed oceans. Liquid water breaks down carbon dioxide, so our carbon dioxide dissolved in the oceans and formed carbonate rocks.

Why didn't Venus form oceans? Venus's closer proximity to the Sun would have resulted in higher surface temperatures. Higher temperatures mean the air can hold more water, and also mean faster evaporation of water. This all results in a positive feedback loop - more water in the atmosphere traps more heat, which in turn leads to even more evaporation and more water vapor in the air. Without oceans, the carbon dioxide also accumulates, and the end result is a runaway greenhouse effect.

Where did the water vapor in the atmosphere go? The sun's ultraviolet rays break down water molecules in the air and cause their hydrogen atoms to escape into space. In the end, all of Venus's water disappeared into space and it was left with only carbon dioxide.