ATLAS OF THE UNIVERSE
Astronomy through the Ages
A
stronomy is certainly the oldest of all the sciences.
Our remote cave-dwelling ancestors must have looked
up into the sky and marvelled at what they saw there, but
they can have had no idea what the universe is really like,
or how vast it is. It was natural for them to believe that the
Earth is flat, with the sky revolving round it once a day
carrying the Sun, the Moon and the stars.
Early civilizations in China, Egypt and the Middle
East divided the stars up into groups or constellations,
and recorded spectacular phenomena such as comets and
eclipses; a Chinese observation of a conjunction of five
bright planets may date back as far as 2449 BC. Probably
the earliest reasonably good calendars were drawn up
by the Egyptians. They paid great attention to the star
Sirius (which they called Sothis), because its ‘heliacal
rising’, or date when it could first be seen in the dawn
sky, gave a reliable clue as to the annual flooding of the
Nile, upon which the whole Egyptian economy depended.
And, of course, there is no doubt that the Pyramids are
astronomically aligned.
The first really major advances came with the Greeks.
The first of the great philosophers, Thales of Miletus, was
born around 624 BC. A clear distinction was drawn
between the stars, which seem to stay in the same posi-
tions relative to each other, and the ‘wanderers’ or plan-
ets, which shift slowly about from one constellation to
another. Aristotle, who lived from around 384 to 325 BC,
gave the first practical proofs that the Earth is a globe, and
in 270 BCEratosthenes of Cyrene measured the size of the
globe with remarkable accuracy. The value he gave was
much better than that used by Christopher Columbus on
his voyage of discovery so many centuries later.
The next step would have been to relegate the Earth
to the status of a mere planet, moving round the Sun in
a period of one year. Around 280 BCone philosopher,
Aristarchus of Samos, was bold enough to champion this
idea, but he could give no firm proof, and found few
supporters. The later Greeks went back to the theory of acentral Earth. Ptolemy of Alexandria, last of the great
astronomers of Classical times, brought the Earth-centred
theory to its highest state of perfection. He maintained
that all paths or orbits must be circular, because the circle
is the ‘perfect’ form, but to account for the observed
movements of the planets he was forced to develop a very
cumbersome system; a planet moved in a small circle or
epicycle, the centre of which – the deferent – itself moved
round the Earth in a perfect circle. Fortunately, Ptolemy’s
great work, the Almagest, has come down to us by way of
its Arab translation.
Ptolemy died in or about the year AD180. There
followed a long period of stagnation, though there was
one important development; in AD570 Isidorus, Bishop of
Seville, was the first to distinguish between true astronomy
and the pseudo-science of astrology (which still survives,
even though no intelligent person can take it seriously).
The revival of astronomy at the end of the Dark Ages
was due to the Arabs. In 813 Al Ma’mun founded the
Baghdad school, and during the next few centuries excel-
lent star catalogues were drawn up. In 1433 Ulugh Beigh,
grandson of the Oriental conqueror Tamerlane, set up an
elaborate observatory at Samarkand, but with his murder,
in 1449, the Baghdad school of astronomy came to an end.
The first serious challenge to the Ptolemaic theory
came in 1543 with the publication of a book by the Polish
churchman Mikol ́aj Kopernik, better known by his
Latinized name Copernicus. He realized the clumsiness
and artificial nature of the old theory could be removed
simply by taking the Earth away from its proud central
position and putting the Sun there. He also knew there
would be violent opposition from the Church, and he was
wise enough to withhold publication of his book until the
end of his life. His fears were well founded; Copernican
theory was condemned as heresy, and Copernicus’ book,
De Revolutionibus Orbium Coelestium(Concerning the
Revolutions of the Celestial Orbs) was placed on the
Papal Index. It remained there until 1835.▲ Copernicus– the
Latinized name of Mikol ́aj
Kopernik, the Polish
churchman whose book,
De Revolutionibus Orbium
Coelestium, published in
1543, revived the theory that
the Earth is a planet moving
round the Sun.▲ Galileo Galilei, the pioneer
telescopic observer, was also
the real founder of the science
of experimental mechanics.
He lived from 1564 to 1642; in
1633 he was brought to trial,
and condemned for daring to
teach the Copernican theory.
The Church finally pardoned
him – in 1992!▲ Isaac Newton(1643–1727),
whose book the Principia,
published in 1687, has been
described as the ‘greatest
mental effort ever made by
one man’, and marked the
true beginning of the
modern phase of astronomy. An orrery, made in 1790;
the name commemorates
the Earl of Cork and Orrery,
for whom the first orrery
was made. The Sun is
represented by a brass ball
in the centre. Around it
move the three innermost
planets, Mercury, Venus
and the Earth; an ingenious
system of gears makes the
planets move round the
Sun in the correct relative
periods, though not at the
correct relative distances.
The Moon’s orbit round
the Earth is inclined at the
correct angle. When the
mechanism is moved, by
turning a handle, the planets
revolve round the Sun and
the Moon revolves round
the Earth. The Zodiacal signs
are shown around the edge
of the disk.B Atl of Univ Phil'03stp 31/3/03 3:55 pm Page 12