Ptolemy, Copernicus and Kepler Ptolemy Ptolemy was a Greek geographer and astronomer/astrologer who probably lived and worked in Alexandria in Egypt from approx. 87 -150 AD. (six hundred years after the original flowering of Greek math and philosophy) Ptolemy was the author of two important scientific treatises. One is the astronomical treatise that is now known as the Almagest ("The Great Treatise"). It was preserved, like most of Classical Greek science, in Arabic manuscripts and only made available in Latin translation in the 12th Century. In this work, one of the most influential books of Antiquity, Ptolemy compiled the astronomical knowledge of the ancient Greek and Babylonian world; he relied mainly on the work of Hipparchus of three centuries earlier. Ptolemy formulated a geocentric model of the solar system which remained the generally accepted model in the Western and Arab worlds until it was superseded by the heliocentric solar system of Copernicus. Perfect motion should be in circles, so the stars and planets, being heavenly objects, moved in circles. However, to account for the complicated motion of the planets, which appear to periodically loop back upon themselves, epicycles had to be introduced so that the planets moved in circles upon circles about the fixed Earth. Copernicus Around 1514, Copernicus distributed a little book, not printed but hand written, to a few of his friends who knew that he was the author even though no author is named on the title page. This book, usually called the Little Commentary, set out Copernicus's theory of a universe with the sun at its centre. The Little Commentary is a fascinating document. It contains seven axioms which Copernicus gives, not in the sense that they are self-evident, but in the sense that he will base his conclusions on these axioms and nothing else What are the axioms? Let us state them: 1. There is no one centre in the universe. 2. The Earth's centre is not the centre of the universe. 3. The centre of the universe is near the sun. 4. The distance from the Earth to the sun is imperceptible compared with the distance to the stars. 5. The rotation of the Earth accounts for the apparent daily rotation of the stars. 6. The apparent annual cycle of movements of the sun is caused by the Earth revolving round it. 7. The apparent retrograde motion of the planets is caused by the motion of the Earth from which one observes.
Ptolemy, Copernicus and Kepler Ptolemy Ptolemy was a Greek
geographer and astronomer/astrologer who probably lived and worked
in Alexandria in Egypt from approx. 87 -150 AD. (six hundred years
after the original flowering of Greek math and philosophy) Ptolemy
was the author of two important scientific treatises. One is the
astronomical treatise that is now known as the Almagest ("The Great
Treatise"). It was preserved, like most of Classical Greek science,
in Arabic manuscripts and only made available in Latin translation
in the 12th Century. In this work, one of the most influential
books of Antiquity, Ptolemy compiled the astronomical knowledge of
the ancient Greek and Babylonian world; he relied mainly on the
work of Hipparchus of three centuries earlier. Ptolemy formulated a
geocentric model of the solar system which remained the generally
accepted model in the Western and Arab worlds until it was
superseded by the heliocentric solar system of Copernicus. Perfect
motion should be in circles, so the stars and planets, being
heavenly objects, moved in circles. However, to account for the
complicated motion of the planets, which appear to periodically
loop back upon themselves, epicycles had to be introduced so that
the planets moved in circles upon circles about the fixed Earth.
Copernicus Around 1514, Copernicus distributed a little book, not
printed but hand written, to a few of his friends who knew that he
was the author even though no author is named on the title page.
This book, usually called the Little Commentary, set out
Copernicus's theory of a universe with the sun at its centre. The
Little Commentary is a fascinating document. It contains seven
axioms which Copernicus gives, not in the sense that they are
self-evident, but in the sense that he will base his conclusions on
these axioms and nothing else What are the axioms? Let us state
them:
1. There is no one centre in the universe. 2. The Earth's centre
is not the centre of the universe. 3. The centre of the universe is
near the sun. 4. The distance from the Earth to the sun is
imperceptible compared with the
distance to the stars. 5. The rotation of the Earth accounts for
the apparent daily rotation of the stars. 6. The apparent annual
cycle of movements of the sun is caused by the Earth
revolving round it. 7. The apparent retrograde motion of the
planets is caused by the motion of the
Earth from which one observes.
Copernicus believed, as all before had believed that heavenly
bodies travelled in perfect circles (they travel in ellipses) so he
need to think of complex corrections to explain actual
observations. Kepler Kepler (1600's) used existing observational
databases to formulate the Laws of Planetary Motion which correct
the problems of epicycles in the heliocentric theory by using
ellipses instead of circles for orbits of the planets. This is a
key mathematical formulation because the reason Copernicus'
heliocentric model has to use epicycles is due to the fact that he
assumed perfectly circular orbits. With the use of ellipses, the
heliocentric model eliminates the need for epicycles and deferents.
It describes the motion of the planets simply and perfectly.
