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”