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:

- Properties we can measure for extrasolar planets
- General conclusions about extrasolar planets
- How extrasolar planets are different



The properties that we can measure for an extrasolar planet depend on which indirect methods of detection we use.

All three indirect methods -- the astrometric, Doppler, and transit methods -- will tell us a planet's orbital period, from which we can determine the average orbital distance.

The astrometric and Doppler methods will also allow us to determine orbital eccentricity, which is how stretched out a planet's orbit is, and estimate planetary mass.

The transit method allows us to measure a planet's size or radius based on how much of a star's light it blocks out during transit, and transit and eclipse observations can also provide limited information about a planet's temperature and atmospheric composition.

Finally, if we have a planet's size from the transit method and its mass from one of the two other methods, then we can calculate the planet's density.



In recent years, the rapid discovery and cataloging of many new planets has allowed scientists to start making some important conclusions about extrasolar planets.

The first conclusion is that planets are common -- at least 70% of all stars have at least one planet.

Another conclusion is that small planets appear to be much more common than large planets, which means Earth-size planets may be very common.

The final conclusion is that extrasolar planets have a much wider range of properties than the planets in our solar system, sometimes in ways that defy our expectations based on what we know about our own solar system.



The fact that our indirect methods of detection are much more likely to detect planets that are close to their star with short orbital periods means our data is far from complete, but what we have found has shown some important differences between extrasolar planets and the planets of our solar system.

First of all, many planets orbit very close to their stars -- much closer than Mercury orbits the Sun -- even though they appear to be massive planets like Jupiter. Many of the planets also have relatively large eccentricities in their orbits, in contrast to the nearly circular orbits of our planets.

Both of these characteristics are at odds with what scientists expected based on the nebular theory. Based on the nebular theory, large planets should form farther from a star. High orbital eccentricities are also not easily explained by the nebular theory, which predicts the nearly circular orbits of our solar system's planets.

Going further, other observations of planets' size, mass, and density have revealed that some extrasolar planets defy easy categorization - they do not always fall neatly into the traditional terrestrial and jovian planetary types. For example, some planets appear to fit the model for "water worlds."