Astronomy and Earth & Planetary Science C12 Letters & Science C70 The Planets

Astronomy and Earth & Planetary Science C12 Letters & Science C70 The Planets Dione Against Saturn & Ring Taken: October 11 2005 Prof. Michael Manga Prof. Geoff Marcy Tu, Th 11-12:30 am VLSB 2050 © 2005 Pearson Education Inc., publishing as Addison-Wesley

Announcements • Waitlist: Everyone will get in ! • Read Chapters 1 & 2 . • Discussion Sections meet this week. • Homework Assignment: Posted on Web. • 7 Problems / Questions • Due: Friday, Tomorrow, Feb 1 • Turn in: Basement of Campbell Hall. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Telescope Observations Project Two Parts 1. Make Telescope Observations of two objects Suggestions: Saturn, Mars, Orion Nebula Telescope Hours: Tue & Thu 7-8 pm, 7th floor of Campbell Hall Sketch both objects on 1/2 sheet of paper. Note Date and Time. Mark the position of Mars with a dot, at three times during the Semester, early, middle, late. (Use either map.) Note date of each observation. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Last Time: Useful Spherical Coordinate System The Celestial Sphere North Celestial Pole Near the ”North Star” . • Stars “glued” to sphere • 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 • every 24 hours: As Earth spins Celestial Equator © 2005 Pearson Education Inc., publishing as Addison-Wesley

Phases of the Moon If the moon were farther away than the Sun, would it ever be a crescent? Today’s Moon: http://www.calculatorcat.com/moon_phases/phasenow.php?tcv=49 © 2005 Pearson Education Inc., publishing as Addison-Wesley

Planets: Moving relative to the StarsObvious 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

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

Ptolemy’sGeocentric 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”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

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

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

Test the Theory that Earth orbits the Sun: Parallax: Apparent shift of a star’s position due to the Earth’s orbiting of the Sun. Greeks didn’t detect parallax ! 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. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Two Possible reasons why stellar parallax was not detected: • Stars are so far away that stellar parallax is too small for naked eye to notice. • 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

Chapter 3: The Science of Astronomy We especially need imagination in science. It is not all mathematics, nor all logic, but is somewhat beauty and poetry. Maria Mitchell (1818 – 1889) Astronomer and first woman elected to American Academy of Arts & Sciences © 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 Carbohydrates make me get fat . . . © 2005 Pearson Education Inc., publishing as Addison-Wesley

Democritus:Pre-SocraticGreekphilosopher(460 - 370 BC). ``There are innumerable worlds ofdifferent sizes. These worlds are at irregular distances, more in one direction and less in another, and some are flourishing, others declining. Some of the worlds have no animal or vegetable life nor any water.” © 2005 Pearson Education Inc., publishing as Addison-Wesley

Epicurus (341-270 B.C.) Greek philosopher in Athens where he opened a school of philosophy “There are infinite worlds both like and unlike this world of ours ... we must believe that in all worlds there are living creatures and plants and other things we see in this world…” © 2005 Pearson Education Inc., publishing as Addison-Wesley

Eratosthenes (276 - 195 BC) • He measured the circumference of the Earth. • The Sun is at the zenith in the city of Syene at noon on the summer solstice. • But at the same time in Alexandria, it is 7 from the zenith. • Eratosthenes inferred that Alexandria was 7 of latitude north of Syene. • The distance between the two cities is 800 km. • Dist = 7/360 times the Earth’s circumference. • His result of 42,000 km is very close to the right number: 40,000 km. © 2005 Pearson Education Inc., publishing as Addison-Wesley

Claudius Ptolemy (AD 100-170) • Theoretical Model of planets, Sun, Moon His model fit the data, made accurate predictions, but was horribly contrived! © 2005 Pearson Education Inc., publishing as Addison-Wesley

Nicolaus Copernicus (1473-1543) 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

Astronomy and Earth & Planetary Science C12 Letters & Science C70 The Planets