Astro 201: Sept. 2, 2010

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1 Astro 201: Sept. 2, 2010 Do on- line prac:ce quiz #2 (see d2l) Homework #2: posted on web page aher class Today: Ancient Greeks Ptolemy V. Copernicus; retrograde mo:on Galileo Astronomical basis for calendars Tycho, Kepler, Newton Despite Aristarchus, for 2000 years, a GEOCENTRIC model of the Universe was favored STARS affixed to the celes:al sphere Moon, Planets and the Sun are between the EARTH and STARS EARTH at the center 1

2 PTOLEMY AD Ptolemy s ALMAGEST was translated into La:n in 1496 GEOCENTRIC: Earth at center Copernicus ( ) Heliocentric Model: Sun at the center 2

Ptolemy s Epicycles In order to understand the mo:on of the planets in the sky Ptolemy s model had to be modified In terms of the heliocentric model, the planets orbit the Sun in ellipses, not

3 Ptolemy s Epicycles In order to understand the mo:on of the planets in the sky Ptolemy s model had to be modified In terms of the heliocentric model, the planets orbit the Sun in ellipses, not circles Retrograde mo:on of the planets with respect to the stars required EPICYCLES Eclip:c the fact that the planets orbit the Sun in a plane means that they always appear to lie on a great circle on the sky, called the eclip&c 3

Retrograde mo:on The planets some:mes appear to be traveling west to east, unlike the stars and Sun which always go east to west Next slide: anima:on Astronomy Picture

4 Retrograde mo:on The planets some:mes appear to be traveling west to east, unlike the stars and Sun which always go east to west Next slide: anima:on Astronomy Picture of the Day for Dec. 20, Jupiter and Saturn showing retrograde mo:on. Combining 23 pictures taken at 2 week intervals from June May Planet = wanderer 4

5 Ptolemy s explana:on for retrograde mo:on of the planets 5

6 Earth Off Center Earth Equant Epicycle Deferent The planet moves along its epicycle as the epicycle moves along the deferent around the Earth. To make the observa:ons as accurate as possible, it was necessary to place the Earth slightly off center of the orbits, but to preserve symmetry that meant that there was an equal place ( Equant ) opposite the Earth from the center. The combined mo:on of the planet and the resul:ng retrograde mo:on are shown. Copernicus explana:on for retrograde mo:on 6

7 Copernicus: On the Revolu:on of the Heavenly Spheres Published at the :me of his death, in 1543 Major Conclusions: 1. The planets orbit the Sun 2. The apparent daily mo:on of the Sun and stars is the result of the Earth s rota:on 3. The stars are much farther away than the Sun Heliocentric model: distance from Sun to stars must be much greater than distance from Sun to Earth. Since Earth orbits Sun, stars should show parallax (a shid in apparent posieon) over the course of half a year. 7

ImplicaEon: distance to stars is several thousand :mes Earth Sun distance.

8 OBSERVATION: Parallax of stars is TOO SMALL to be seen by the naked eye. Not observed un:l 1800s. ImplicaEon: distance to stars is several thousand :mes Earth Sun distance. Parallax Unit of distance: the PARSEC A star which is one parsec from Earth shows a parallax of one arcsecond d = 1 p Remember: 360 degrees in a circle, 60 arcminutes per degree, 60 arcseconds per arcminute 8

MarEn Luther (1483-1546): [Copernicus] is a fool who wishes to reverse the en:re scheme of astronomy; but sacred scripture tells us that Joshua commanded the Earth to stand

9 Reac:ons to Copernicus: On March 5, 1616, Copernicus' work was banned from being taught and discussed by the Congrega:on of the Index "un:l corrected." It stayed on this list of prohibited books and teachings un:l MarEn Luther ( ): [Copernicus] is a fool who wishes to reverse the en:re scheme of astronomy; but sacred scripture tells us that Joshua commanded the Earth to stand s:ll, not the Sun. Giordano Bruno ( ): burned at the stake for advoca:ng that stars are suns in their own right, and that there is a plurality of worlds like the Earth. Cosmological Models: Version 1.0: Superdome model v. 1.0 Version 2.0: Geocentric model v. 2.0 Version 3.0: Heliocentric model v

10 Which is right? Occam's Razor: Pluralitas non est ponenda sine neccesitate "plurality should not be posited without necessity." Given a set of otherwise equivalent models of a phenomenon, the simplest one is the best. Keep it simple, stupid. William of Occam English philosopher from Ockham Franciscan Monk Got into trouble with the Pope for advoca:ng apostolic poverty Died of the Black Death while in exile Advocated Epistomological Parsimony c.f. Ontological parsimony Epistomology = theory of knowledge Ontology = what exists? 10

Galileo Galilei (1564 1642) Italian First to use a telescope to look at

the Sun rotates The Moon has mountains, craters, rocky surface with

the sky WITH MOONS that orbit it Venus has PHASES like the MOON Galileo

11 Galileo Galilei ( ) Italian First to use a telescope to look at the sky 1610 Siderius Nuncius (The Starry Messenger) Spots on the Sun; the Sun rotates The Moon has mountains, craters, rocky surface with imperfec:ons The planet Jupiter is not a pinpoint star but a disc in the sky WITH MOONS that orbit it Venus has PHASES like the MOON Galileo Galilei ( ) Spots on the Sun The Sun rotates Eventually went blind 11

Galileo Galilei (1564 1642) The Moon Has Mountains and Valleys Galileo Galilei (1564

of the moon from full to crescent, which it must do if the Copernican theory was

12 Galileo Galilei ( ) The Moon Has Mountains and Valleys Galileo Galilei ( ) Phases of Venus Galileo observed that Venus showed phases en:rely like those of the moon from full to crescent, which it must do if the Copernican theory was correct. According to the Ptolemaic theory Venus would have to be a perpetual crescent. 12

13 Observa:ons consistent with Copernicus, inconsistent with Ptolemy. Galileo Galilei ( ) Jupiter Has Moons Galilean Moons 4 Largest moons of Jupiter Io, Europa, Callisto, & Ganymede 13

Galileo Galilei (1564 1642) 1632: "Dialogo Dei Massimi Sistemi Dialogue on the Two Chief World Systems In Italian, Not Latin -- For the common people Two people, one representing the view of Ptolemy

14 Galileo Galilei ( ) 1632: "Dialogo Dei Massimi Sistemi Dialogue on the Two Chief World Systems In Italian, Not Latin -- For the common people Two people, one representing the view of Ptolemy and other the view of Copernicus, present their arguments before an intelligent layman. The Pope Urban II thought that Simplico, the character who upheld the views of Ptolemy in the book, was a deliberate and insul:ng caricature of himself 1633: Trial by Church (threatened with instruments of torture), forced to recant views "Eppur Si Muove "(And, yet it moves!") 1633: Galileo is ordered to his house in Arcetri, under house arrest, where he remains for the rest of his life. The book remained on the index of forbidden books un:l 1822 Pope John Paul II finally gave an address that admived that there had been errors in the treatment of Galileo by the church, in ASIDE: Contrast Galileo with Nicolas Steno ( ), who laid the groundwork for the interpreta:on of the fossil record. See The Seashell on the Mountaintop by Alan Cutler. 14

15 Modern Scien:fic Method 1. Observa:ons and Experiments Data which describes the physical world 2. Theory, Hypotheses, Models: - > Organize Facts from experiment & observa:ons Unifying principles Make testable predic:ons Crea:onism and Intelligent Design vs. Evolu:on. The example of gravity as a scien:fic theory: Newton s Law c AD Einstein s theory of General Rela:vity c Photon versus wave descrip:on of light The most intereseng scienefic queseons to work on for a professional scienest are those we don't know the answer to. InteresEng theories to work on are those which fail to explain an observaeon or fact. Many modern astronomers are deeply religious people. 15

Astro 201: Aug. 26, 2010

Astro 201: Aug. 26, 2010 Turn in HW #1 in front of room Pick up Telescope Lab Handout Reading: Hester et al: Chapter 2 Gleiser: Chapters 1-6 Wait List students have been added; class limit will be increased,