The Science Book

20

B

orn 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 May 28,

585 BCE, which famously brought a

battle between the warring Lydians

and Medes to a halt.

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. ■

ECLIPSES OF

THE SUN CAN

BE PREDICTED

THALES OF MILETUS (624 –546 BCE)

IN CONTEXT

BRANCH

Astronomy

BEFORE

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.

AFTER

c.140 BCE Greek astronomer

Hipparchus develops a

system to predict eclipses

using the Saros cycle of

movements of the Sun

and Moon.

...day became night, and this

change of the day Thales the

Milesian had foretold...

Herodotus

See also: Zhang Heng 26–27 ■ Nicolaus Copernicus 34–39 ■

Johannes Kepler 40–41 ■ Jeremiah Horrocks 52