26
See also: The geocentric model 20 ■ The Copernican model 32–39 ■
The Tychonic model 44–47 ■ Elliptical orbits 50–55F
rom the 4th century bce
to the 16th century ce, the
prevailing view throughout
the Western world was that Earth
is stationary and located at the
center of the universe. Suggestions
that Earth might be rotating were
dismissed on the grounds that
this would cause objects on Earth’s
surface to fly off into space. In India,
however, an astronomer named
Aryabhata was convinced that
the movement of stars across the
night sky was due not to the stars
revolving in a distant sphere around
Earth, but to Earth itself rotating.An illusory movement
According to Aryabhata, the stars
were stationary and their apparent
movement toward the west was an
illusion. His notion of a spinning
Earth was not widely accepted
until the mid-17th century—a
century after Nicolaus Copernicus
had endorsed the idea.
Aryabhata’s achievements were
considerable. His book Aryabhatiya
was the most important work of
astronomy in the 6th century.Essentially a compendium of the
fundamentals of astronomy and
relevant mathematics, it greatly
influenced Arabic astronomy.
Among other achievements,
Aryabhata calculated the length
of the sidereal day (the time it
takes Earth to rotate once in
relation to the stars) to a high
degree of accuracy, and devised
original and accurate ways of
compiling astronomical tables. ■THE UNMOVING
STARS GO UNIFORMLY
WESTWARD
EARTH’S ROTATION
IN CONTEXT
KEY ASTRONOMER
Aryabhata (476–550 ce)BEFORE
350 bce Heraclides Ponticus,
a pupil of Plato, proposes that
Earth rotates once a day on
its axis. The idea does not
become widespread because
it contradicts Aristotle, who is
considered more authoritative.4th century bce Aristotle
states that Earth is stationary
in space.AFTER
950 ce Iranian astronomer
al-Sijzi supports the idea
that Earth rotates.
1543 Nicolaus Copernicus
states that Earth rotates
as part of his heliocentric
(sun-centered) model of
the universe.1851 The first demonstration
of Léon Foucault’s pendulum
in Paris provides the final
scientific proof that Earth
is rotating.He was the father of the
Indian cyclic astronomy ...
that determines more
accurately the true positions
and distances of the planets.
Helaine Selin
Historian of astronomy