Summary Notes Lectures 1-3 Dennis Papadopoulos Astr 340 Fall 2006

Parallax Angle -Parsec The distance d that produces one second of arc parallax over the baseline of the earth’s orbit is called a parsec. A parsec corresponds to 3.26 light-years d=2 AU/2 p=AU/p parsec= (360x60x60)(AU/2)=3.1X10 16 m

1. Pre-6 th century BC: Everything explained in terms of myths, gods and monsters 2. 6 th Century BC Greece: Philosophers start to describe Universe in terms of natural phenomena and not supernatural designs GREEK PROTOSCIENTISTS SOUGHT THEORIES AND MODELS Simple Accurate Natural Viable The art of measurements: First measurement ladder Sizes and distances of and between earth, moon, sunUSING Experiment/Observations Logic/Theory (+mathematics) Greek astronomers established earth centered model 3. When earth centered model proved inconsistent with observations they tried a patchwork – ad hoc fixes- Ptolemy’s epicycles Religion encouraged scientists to stay with earth centered model because it was consistent with the bible

4. Forward to 16 th Century-> Copernicus reinstates Aristarchos’ heliocentric Model – Sun and other planets orbit the Sun in circular orbits. Simple, and reasonably accurate Ignored because he was virtually unknown model defied common sense model less accurate than Ptolemy’s religious orthodoxy crashed with original thought – intelligent design 5. Keppler using Tycho Brahe’s observations showed that Copernicus heliocentric model should be modified so that the planets follow elliptical rather than circular orbits. New model simpler and more accurate than Copernican. 6. Enter Galileo: Championed heliocentric model. Used telescope to show That Jupiter has moons, Sun has spots and Venus has phases that supported heliocentric and were inconsistent with geocentric theories. Church bullied him to recant his beliefs in By 1900 cosmologists concluded that the Universe was not created but had existed for eternity but there was no evidence to back it. The eternal Universe hypothesis was no more than a myth th century cosmologist return to the big question. Was the Universe created or existed for all eternity ?

Solar system orbits Inner planets Outer planets Note the low eccentricities!