Longitude

Definition: Claudius Ptolemy, the Greek philosopher from Alexandria who lived from about 90-168 A.D., wrote a very influential Geography and used lines of latitude and longitude to locate places on his maps. Such lines are thought to have been first applied to earth measurement in the second century B.C. by Hipparchus of Nicea (in Bithynia), an astronomer, whose work advanced Babylonian calculations. Hipparchus found a ratio between day lengths to determine latitude. The lines of longitude he thought could be found on the basis of solar eclipses. Hipparchus could not carry out such measurements. He proposed a zero meridian of longitude through Rhodes. Other lines of longitude go east and west of this line. Lines of longitude are vertical.