Transcript Day 03
Announcements •Let me know the book you want to do your 1st project on as soon as you decide. First-comefirst-served with no duplication allowed. One book has already been chosen. •The first Dark Sky Observing Night is next Tuesday night. Activities start at 7:30 so set-up begins at 6:30. Chapter 2 Astronomy in Antiquity Ptolemy and the Earth centered universe Babylonian Chaldean Tablet The Enuma Anu Enlil was a compilation of bad omens By observing over centuries the Babylonians could detect cycles Babylonian Number System Babylonian Calendar The Metonic Cycle was one of the cycles they observed 235 lunar cycles = 19 solar cycles +7 so add seven intercalary months every 19 years to “even” it out Egyptian culture was centered on the annual flooding of the Nile Thus the year is divided into three seasons: the Flood, the Subsiding and the Harvest Egyptian Calendars The administrative calendar had 365 days in every year The lunar calendar had “intercalary” months inserted occasionally to keep synchronized with the seasons Calendars were “synched” with the helical rising of Sirius The Greeks Aristotle Plato Aristarchus Eratosthenes His value of the circumference of the Earth of 250,000 stadia is probably not far off. The Spheres of Eudoxus Plato and the requirement of circles and spheres Aristotle and Physics Aristotle defined two types of motion: natural and forced Falling bodies were a natural motion. The more massive something is, the faster it will fall. The motion of an arrow through the air is a forced motion. The force is originally applied by the bow and then by the air After Alexander the Great, Greek astronomy became more “precise” The Spheres of Eudoxus worked OK for the Moon but were way off for the planets Post-Alexander, Aristarchus attempted to measure the distance to the Sun by measure the Earth-Sun-Moon angle at quadrature Appolonius was the first to propose the eccentric and epicycle Hipparchus made it a model capable of prediction Hipparchus also measured stellar positions precisely enough to discover the Precession of the Equinoxes Hipparchus also modeled the changing speed of the sun Ptolemy built on Hipparchus’ work and added the Equant The Complete Ptolemaic System The Almagest was THE book on astronomy for almost 1500 years Originally titled “Megale Syntaxis” later known as the “Greatest Compilation”