The Science Book

27

See also: Nicolaus Copernicus 34–39 ■ Johannes Kepler 40–41 ■
Isaac Newton 62–69

THE BEGINNING OF SCIENCE

with Earth at its center. Zhang
catalogued 2,500 “brightly shining”
stars and 124 constellations, and
added that “of the very small stars
there are 11,520.”

Eclipses of the Moon
and planets
Zhang was fascinated by eclipses.
He wrote, “The Sun is like fire and
the Moon like water. The fire gives
out light and the water reflects it.
Thus the Moon’s brightness is
produced from the radiance of the

Sun, and the Moon’s darkness is

due to the light of the Sun being

obstructed. The side that faces the

Sun is fully lit, and the side that is

away from it is dark.” Zhang also

described a lunar eclipse, where

the Sun’s light cannot reach the

Moon because Earth is in the way.

He recognized that the planets

were also “like water,” reflecting

light, and so were also subject to

eclipses: “When [a similar effect]

happens with a planet, we call it an

occultation; when the Moon passes

across the Sun’s path then there is

a solar eclipse.”

In the 11th century, another

Chinese astronomer, Shen Kuo,

expanded on Zhang’s work in one

significant respect. He showed that

observations of the waxing and

waning of the Moon proved that the

celestial bodies were spherical. ■

The Moon and the planets

are Yin; they have shape

but no light.

Jing Fang

Zhang Heng

Zhang Heng was born in 78 CE

in the town of Xi’e, in what is

now Henan Province, in Han

Dynasty China. At 17, he left

home to study literature and

train to be a writer. By his late

20s, Zhang had become a

skilled mathematician and

was called to the court of

Emperor An-ti, who, in 115 CE,

made him Chief Astrologer.

Zhang lived at a time of

rapid advances in science. In

addition to his astronomical

work, he devised a water-

powered armillary sphere (a

model of the celestial objects)

and invented the world’s first

seismometer, which was

ridiculed until, in 138 CE, it

successfully recorded an

earthquake 250 miles (400 km)

away. He also invented the

first odometer to measure

distances traveled in vehicles,

and a nonmagnetic, south-

pointing compass in the form

of a chariot. Zhang was a

distinguished poet, whose

works give us vivid insights

into the cultural life of his day.

Key works

c.120 CE The Spiritual

Constitution of the Universe

c.120 CE The Map of

the Ling Xian

The crescent outline of Venus is

about to be occulted by the Moon.

Zhang’s observations led him to

conclude that, like the Moon, the

planets did not produce their own light.