The Astronomy Book

334

ANAXIMANDER OF MILETUS

610–546 BCE

Greek philosopher Anaximander

provided one of the earliest

attempts at a rational explanation

of the universe. He speculated that

the celestial bodies made full circles

around Earth, which led him to the

conclusion that Earth must float

freely and unsupported in space. He

also stated that celestial bodies lie

behind one another, meaning that

there was depth to the universe—

the first recorded conception of the

idea of “space.” Anaximander placed

the celestial bodies in the wrong

order, however, believing that the

stars were nearest to Earth, followed

by the moon, and then the sun.

See also: The geocentric model 20

ERATOSTHENES

c.276–c.194 BCE

The third chief librarian at the

famous Library of Alexandria,

Greek scholar Eratosthenes

made major contributions to the

field of geography. He measured

vernal equinoxes), and the lunar

month. He used his calculations to

predict four solar eclipses correctly.

Zu measured the length of Jupiter’s

year as 11.858 Earth years, which is

less than 0.1 percent away from the

current accepted figure.

See also: The solar year 28–29

AL-BATTANI

c.858–929

Arab astronomer and

mathematician Al-Battani made

accurate observations to refine

the figures for the length of the

year, the inclination of the ecliptic,

and the precession of the equinoxes.

He developed trigonometric

methods to improve on Ptolemy’s

calculations, and showed that

the distance of the sun from Earth

varies over time. Al-Battani’s most

influential work was a compilation

of astronomical tables, which

was translated into Latin in the

12th century and was a major

influence on Copernicus.

See also: Consolidating knowledge

24–25 ■ The Copernican model

32–39

DIRECTORY

F

or a field of enquiry as broad as astronomy, there has not been

room to include every significant scientist as a main entry in

this book. The following pages list astronomers who have also

made important contributions across time, from the 7th century BCE to

the present day. In its early stages, astronomy usually involved individuals

or small groups making observations and calculations. Modern high-tech

“big astronomy,” meanwhile, often requires large-scale collaborations

of hundreds or thousands of scientists. Whether they are booking time

for an experiment at a particle accelerator or requesting that a space

telescope be pointed in a particular direction, today’s astronomers form

part of a huge community developing the big ideas of tomorrow.

the circumference of Earth

by comparing the angle of the

noon shadow at midsummer in

Alexandria with that in Syene

(present-day Aswan). He knew the

distance between the two locations,

and his measurement allowed him

to figure out the proportion of the

entire circumference that this

represented. He also produced

an accurate measurement of Earth’s

axial tilt, measured the distances

to the sun and the moon, introduced

the leap day to correct the length

of the year, and produced one of

the first ever maps of the world.

See also: Consolidating

knowledge 24–25

ZU CHONGZHI

429–500 CE

Tasked with producing a new

calendar by the Emperor Xiaowu,

Chinese mathematician Zu

Chongzhi made highly accurate

measurements of the lengths of

the sidereal year (Earth’s rotation

period measured relative to the

background stars), the tropical year

(the period between successive