IN CONTEXT
Astronomy
c.2000 BCE European monuments such as Stonehenge may have been used to calculate eclipses.
c.1800 BCE In ancient Babylon, astronomers produce the first recorded mathematical description of the movement of heavenly bodies.
2nd millennium BCE Babylonian astronomers develop methods for predicting eclipses, but these are based on observations of the Moon, not mathematical cycles.
c.140 BCE Greek astronomer Hipparchus develops a system to predict eclipses using the Saros cycle of movements of the Sun and Moon.
Born in a Greek colony in Asia Minor, Thales of Miletus is often viewed as the founder of Western philosophy, but he was also a key figure in the early development of science. He was recognized in his lifetime for his thinking on mathematics, physics, and astronomy.
Perhaps Thales’s most famous achievement is also his most controversial. According to the Greek historian Herodotus, writing more than a century after the event, Thales is said to have predicted a solar eclipse, now dated to 28 May 585 BCE, which famously brought a battle between the warring Lydians and Medes to a halt.
"…day became night, and this change of the day Thales the Milesian had foretold…"
Herodotus
Contested history
Thales’s achievement was not to be repeated for several centuries, and historians of science have long argued about how, and even if, he achieved it. Some argue that Herodotus’s account is inaccurate and vague, but Thales’s feat seems to have been widely known and was taken as fact by later writers, who knew to treat Herodotus’s word with caution. Assuming it is true, it is likely that Thales had discovered an 18-year cycle in the movements of the Sun and Moon, known as the Saros cycle, which was used by later Greek astronomers to predict eclipses.
Whatever method Thales used, his prediction had a dramatic effect on the battle at the river Halys, in modern-day Turkey. The eclipse ended not only the battle, but also a 15-year war between the Medes and the Lydians.
See also: Zhang Heng • Nicolaus Copernicus • Johannes Kepler • Jeremiah Horrocks