|
|
Ptolemy
Ptolemy's geocentric univers.
Ptolemy (AD 100?-170?), astronomer and
mathematician, whose astronomical theories and explanations
dominated scientific thought until the 16th century. He is also
remembered for his contributions to the fields of mathematics,
optics, and geography. Ptolemy was probably born in Greece, but
his actual name, Claudius Ptolemaeus, reflects all that is really
known of him: “Ptolemaeus” indicates that he was a
resident of Egypt, and “Claudius” signifies Roman
citizenship. In fact, ancient sources report that he lived and
worked in Alexandria, Egypt, for most of his life.
Ptolemy's earliest and most famous work,
originally written in Greek, was translated into Arabic as
al-Majisti (Great Work). In Europe, medieval Latin translations
reproduced the title as Almagesti, and it has since become known
simply as the Almagest. In this work, Ptolemy proposed a
geometric theory to account mathematically for the apparent
motions and positions of the planets, sun, and moon against a
background of unmoving stars. This work did not include any
physical descriptions of objects in space.
Ptolemy began by accepting the generally
held theory that the earth did not move but was at the center of
the universe. The planets and stars were considered, for
philosophical reasons, to move continuously in perfectly circular
orbits. He then elaborated on the theory in an attempt to account
for the astronomical puzzles that the theory presented, such as
the apparent backward motions of the planets and apparent
variations in size or brightness of the moon and planets. Ptolemy
proposed that the planets, sun, and moon moved in small circles
around much larger circles, in which the earth was centered. In
this way, he made his system fit most of the observations that
astronomers had recorded.
Ptolemy used the term
epicycle to describe the small circle around which he claimed
objects in space move. To make his theory of epicycles appear
sound, he had to introduce variations from traditional
mathematics. This departure from traditional assumptions was one
reason the Polish astronomer Nicolaus Copernicus rejected
Ptolemy's system in the 16th century and developed his own
heliocentric theory, which correctly stated that the sun was
located at the center of the solar system. Even so, Copernicus
retained an elaborate system of epicycles.
( Ptolemy - Copernicus - Kepler - Galileo - Newton )
quarksup@fcmail.com
Copyright JoaoVicente.
Last update: 11/02/98.
