© 2005 Pearson Education Inc., publishing as Addison-Wesley The Planets Prof. Geoff Marcy Eclipses Geocentric vs Heliocentric Theory The Nature of Scientific Theories Lecture 4

© 2005 Pearson Education Inc., publishing as Addison-Wesley Announcements Read Chapters 2 & 3 ! Discussion Sections! Homework Assignments: - Assignment Chapters. 1&2: Due Fri (!) at 6pm - Assignment Chapt. 3: Due Fri at 6pm -Observation Project: Due this Thu. in class Moonrise over Berkeley Hills: ~11pm Tue, Wed, Thu 12-1: Disc. Sections Not full!

Curiosity Landing on Mars 5 August 2012

© 2005 Pearson Education Inc., publishing as Addison-Wesley Review of Last Lecture

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Celestial Sphere North Celestial Pole Near the ”North Star”. Stars appear “glued” to sphere actually at different distances. Constellations: Apparent groupings North & South “Celestial poles” Celestial equator Ecliptic: Sun’s path against the stars = Orbital plane of Earth Celestial Sphere Rotates around us Celestial Sphere Rotates around us every 24 hours: As Earth spins every 24 hours: As Earth spins Useful Spherical Coordinate System Last Time:

© 2005 Pearson Education Inc., publishing as Addison-Wesley Motion of the Night Sky as hours pass 1.From Berkeley 2.From the Equator 3.From the North Pole

© 2005 Pearson Education Inc., publishing as Addison-Wesley Berkeley Hills

© 2005 Pearson Education Inc., publishing as Addison-Wesley

Moon: Going through phases each 29.5 Days (one orbital period)

© 2005 Pearson Education Inc., publishing as Addison-Wesley If you stand on the Moon, does the Earth go through “phases” ? When Earthlings see a crescent moon, what is the phase of the Earth, as seen from the Moon? a.New b.Crescent c.Quarter d.Gibbous Yes !

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Section 1 What do they look like? Why do they happen? Eclipses: Solar and Lunar

© 2005 Pearson Education Inc., publishing as Addison-Wesley Eclipses Solar Eclipse Solar Eclipse: Moon blocks the Sun Sun is behind the moon: Only occurs at new moon You are in the Moon’s shadow. within umbra: total solar eclipse within penumbra: partial solar eclipse

© 2005 Pearson Education Inc., publishing as Addison-Wesley 2002 total Solar Eclipse Ceduna, Australia Dec 4, 2002

© 2005 Pearson Education Inc., publishing as Addison-Wesley Solar Eclipse

© 2005 Pearson Education Inc., publishing as Addison-Wesley Solar Eclipse 1999 Aug 11 from the Russian Mir Space Station

© 2005 Pearson Education Inc., publishing as Addison-Wesley Eclipses The Earth & Moon cast shadows. When either passes through the other’s shadow, we have an eclipse. Why don’t we have an eclipse every full & new Moon? Sun

© 2005 Pearson Education Inc., publishing as Addison-Wesley Total Solar Eclipse Lusaka, Zambia 2001

© 2005 Pearson Education Inc., publishing as Addison-Wesley Solar Eclipse in India 24 October 1995 By: Solar Physicsts Wendy Carlos and Fred Espenak India

Solar Eclipse May Just after Finals Last Spring Sproul Plaza

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Solar Eclipse Predictions

© 2005 Pearson Education Inc., publishing as Addison-Wesley Total Solar Eclipse: 21 Aug 2017

Solar Eclipse: Aug 21, 2017 © 2005 Pearson Education Inc., publishing as Addison-Wesley

Lunar Eclipses

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Section 2 A Model of the Solar System: Geocentric vs Heliocentric

© 2005 Pearson Education Inc., publishing as Addison-Wesley We see only one side of the Moon

© 2005 Pearson Education Inc., publishing as Addison-Wesley Why we always see the same face of the Moon Rotation period = orbital period Earth Not Correct Model Moon Correct Model Earth Moon

© 2005 Pearson Education Inc., publishing as Addison-Wesley Build a model, i.e. conceptual theory, of the Solar System Conceptual models must explain all the motions of the planets: i.e., the “data”...

© 2005 Pearson Education Inc., publishing as Addison-Wesley Planets: Moving relative to the Stars Obvious to the eye Mercury –Difficult to see; Always angularly close to Sun Venus –Very bright. Always near Sun— morning or evening “star” Mars –Noticeably orange. Usually moves west-to-east –Sometimes backwards “retrograde” ! Jupiter –Very bright. Moves west-to-east against stars. Saturn –Moderately bright. Moves more slowly west-to-east.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Motion of the Planets Relative to the Earth during several years The Sun and planets seem to orbit the earth during months and years. Earth

© 2005 Pearson Education Inc., publishing as Addison-Wesley The Motion of Planets The Planets normally move West to East against the background stars. Why do planets sometimes seem to move backwards relative to the stars? Greeks concluded that the planets orbit the Earth. Why did smart people conclude this?

© 2005 Pearson Education Inc., publishing as Addison-Wesley Observed Motion of Mars: Normal & “Retrograde” ”

© 2005 Pearson Education Inc., publishing as Addison-Wesley To Explain Retrograde Motion Two Models: Geocentric Heliocentric

© 2005 Pearson Education Inc., publishing as Addison-Wesley Ptolemy’s Geocentric Model Earth is at center Sun orbits Earth Planets orbit on small circles whose centers orbit the Earth on larger circles (The small circles are called epicycles)

© 2005 Pearson Education Inc., publishing as Addison-Wesley In Heliocentric “model” In Heliocentric “model” Retrograde Motion is a Natural Consequence Planets usually appear to move eastward relative to the stars. But as we pass by them, planets seem to move west relative to the stars. Only noticeable over many nights; on a single night, a planet rises in east and sets in west…

© 2005 Pearson Education Inc., publishing as Addison-Wesley Earth-Centered Theory Sun-Centered Theory Which theory Seems “Best” ? Two Theories::

© 2005 Pearson Education Inc., publishing as Addison-Wesley Choosing the Best Model: Explaining Retrograde Motion Natural result of Heliocentric Model Difficult to explain if Earth is at center The Best “Model” or “Theory” explains various data and phenomena with the fewest assumptions. “Occam’s Razor “: Choose the simplest model that explains all the data.

© 2005 Pearson Education Inc., publishing as Addison-Wesley 3D “model” of the Solar System

© 2005 Pearson Education Inc., publishing as Addison-Wesley Why did the Greeks reject the theory that the Earth orbits the Sun? It ran contrary to their common sense: Every day, the sun, moon, and stars rotates around us. So, we “must be” at the center... If the Earth rotated, then there should be a “great wind” as we moved through the air. Greeks knew that we should see stellar “parallax” if we orbited the Sun – but they could not detect it.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Parallax: Apparent shift of a star’s position due to the Earth’s orbiting of the Sun. The nearest stars are much farther away than the Greeks thought. The parallax angles of the stars are so small, that you need a telescope to observe them. Test the Theory that Earth orbits the Sun: Greeks didn’t detect parallax !

© 2005 Pearson Education Inc., publishing as Addison-Wesley Two Possible reasons why stellar parallax was not detected: 1.Stars are so far away that stellar parallax is too small for naked eye to notice. 2.Earth does not orbit Sun; it is the center of the universe. Debate about theory: Earth-centered vs. Sun-centered Planetary System.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Section 3 Scientific Theory: What is a good “Theory” ?

© 2005 Pearson Education Inc., publishing as Addison-Wesley Scientific Thinking It is a natural part of human curiosity: Search for understanding and truths that explain many facts. We draw conclusions based on our experiences. Progress is made through “trial and error.” Hypothesize. Then test your hypothesis. Eating pasta makes me get fat...

© 2005 Pearson Education Inc., publishing as Addison-Wesley Nicolaus Copernicus ( ) He thought Polemy’s model was contrived Yet he believed in circular motion De Revolutionibus Orbium Coelestium

© 2005 Pearson Education Inc., publishing as Addison-Wesley Copernicus’ Heliocentric Model Sun is at center Earth orbits like any other planet Inferior planet orbits are smaller Retrograde motion occurs when we “lap” Mars & the other superior planets

© 2005 Pearson Education Inc., publishing as Addison-Wesley Johannes Kepler ( ) Greatest theorist of his day Imagined planets on “heavenly spheres”

© 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s Laws 1. Each planet’s orbit around the Sun is an ellipse, with the Sun at one focus.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Eccentricity of an Ellipse

© 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s 2nd Law A planet moves along its orbit with a speed that changes in such a way that a line from the planet to the Sun sweeps out equal areas in equal intervals of time.

© 2005 Pearson Education Inc., publishing as Addison-Wesley Kepler’s 3rd Law The cube of a planet’s average distance from the Sun is equal to the square of its orbital period. (Use units of years and AUs.) a 3 = P 2