Announcements Let me know the book you want to do your 1 st project on as soon as you decide....
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Transcript of Announcements Let me know the book you want to do your 1 st project on as soon as you decide....
Announcements• Let me know the book you want to do your 1st project
on as soon as you decide. First-come-first-served with no duplication allowed. Two books have already been chosen.
• The first Dark Sky Observing Night is tomorrow night. Activities start at 8:30 so set-up begins at 7:30. Current weather forecast is iffy so watch APSU Astronomy for a possible cancellation notice.
• The first of only two 1st Quarter Observing Nights is next Thursday. It, too, starts at 8:30 so set-up will begin at 7:30pm.
Chapter 2Astronomy in Antiquity
Ptolemy and the Earth centered universe
Babylonian Chaldean
Tablet
The Enuma Anu Enlil was a compilation of bad omens
By observing the sky over centuries, the Babylonian astronomers saw repetitions of 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
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
Falling bodies were a natural motion. The more massive something is, the faster it will fall.
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”