The Astronomy Book

27

See also: Consolidating knowledge 24–25 ■ Examining nebulae 104–05 ■

Spiral galaxies 156–61 ■ Beyond the Milky Way 172–77

A

bd al-Rahman al-Sufi, once

better known in the West

as Azophi, was a Persian

astronomer who made the first

record of what are now understood

to be galaxies. To al-Sufi, these

fuzzy, nebulous objects looked like

clouds in the night’s sky.

Al-Sufi made most of his

observations in Isfahan and Shiraz,

in what is now central Iran, but he

also consulted Arab merchants

who traveled to the south and

east, and who saw more of the sky.

His work centered on translating

Ptolemy’s Almagest into Arabic.

In the process, al-Sufi tried to

merge the Hellenistic constellations

(which dominate star maps today)

with their Arab counterparts, most

of which were totally different.

The fruit of this labor was

Kitab suwar al-kawakib, or the Book

of Fixed Stars, published in 964 ce.

The work contained an illustration

of “a little cloud,” which is now

know to be the Andromeda Galaxy.

This object was probably known

to earlier Persian astronomers, but

al-Sufi’s mention is the earliest

record. Similarly, The Book of

Fixed Stars includes the White

Ox, another cloudy object. This is

now named the Large Magellanic

Cloud and is a small galaxy that

orbits the Milky Way. Al-Sufi would

not have been able to observe

this object himself, but would

have received reports of it from

astronomers in Yemen and sailors

who crossed the Arabian Sea. ■

FROM MYTH TO SCIENCE

A LITTLE CLOUD

IN THE NIGHT SKY

MAPPING THE GALAXIES

IN CONTEXT

KEY ASTRONOMER
Abd al-Rahman al-Sufi
(903–986 ce)

BEFORE
400 bce Democritus suggests
that the Milky Way is made
of a dense mass of stars.

150 ce Ptolemy records several
nebulae (or cloudy objects)
in the Almagest.

AFTER
1610 Galileo sees stars
in the Milky Way using
a telescope, confirming
Democritus’s theory.

1845 Lord Rosse makes the
first clear observation of a
spiral nebula, now known
as the Whirlpool Galaxy.

1917 Vesto Slipher discovers
that spiral nebulae are rotating
independently of the Milky Way.

1929 Edwin Hubble shows
that many spiral nebulae are
far beyond the Milky Way
and are galaxies themselves.

The Large Magellanic Cloud,

seen here above the ESO’s Paranal

observatory in Chile, can be easily

observed with the naked eye from

the southern hemisphere.