Ptolemaic system developed in ancient Greece:

Geometrical model of universe – used to discover the “precession of the equinoxes”

precession of the equinoxes

Gnomon at Dengfeng; ca.1250 ADGuo Shoujing measures length of year to accuracy of about

half a minute in 1280 AD

Observatory at Samarkand,

ca. 1450

Al Battani measures tilt of ecliptic to within one

hundredth of a degree: ca.

900 A.D.

• ca. 1600: Tycho Brahe and his observatory