Greek Astronomy - Ptolemy
The issue of
geocentrism vs. heliocentrism appeared settled by Ptolemys great work,
the Almagast Here is a Greek astronomer (writing between 127 and 141 A.D.) who
organized a series of highly complex and creative mathematics to explain the
motion of the sun and other objects. The book is 13 volumes long and would fill
500 pages when translated into modern language, and the complicated epicycle
motions of the planets.
An interesting phenomenon was his curiosity into reports of sailors seeing
boats rise up out of the sea (the "hull-down" effect), and even whole
islands doing so. While many presently hold to the actual historical existence
of Atlantis, there may be another explanation for the rising and sinking of
this fabled city. To any sailor who ventured far enough out to sea, any distant
boat would have its hull down under the water until it neared, and sailors could
see all of it rising from the sea. This "hull-down" effect took place
in any direction on the ocean. While this effect was not recorded before 10
B.C., Ptolemy was one of the first to really try to explain it. Any distant
island would look as if it were rising up as one approached it. The diagram
demonstrates how this is possible. Sailors did not think about the oddity that
the island was never completely visible. They could see the tip of the island
and more of the base as they approached it, never seeing the entire island until
relatively close. If the Earth were flat, the entire island should be visible
from any distance. That the island became more visible in terms of total island,
was evidence for the physical rising and falling of the piece of land. The second
diagram demonstrates Aristotle's deduction. A curved earth surface would result
in a line of sight for the view missing the base of the island below that same
line of sight. Sailors may have been excited about Atlantis rising and falling
mysteriously into the sea, but Ptolemy had a more practical idea of this phenomenon.
Ptolemy wrote his
great book with the mindset that Earth occupied the center of the universe.
His geocentric model is found in the drawing below. Each sphere out from the
earth was occupied by a celestial object, moving in perfectly circular paths.
Since the retrograde motion of the outer planets made such circular orbits impossible,
Ptolemy carefully worked out a series of smaller circular motions within the
larger circular orbit. He coined the small motions "epicycles." Clearly
a 13 volume book with detailed mathematics was daunting to the average citizen,
even if they had time to digest the work while philosophizing at the Agora.
It was easier to accept the idea than to ponder it, and besides, basic survival
required more attention than astronomical musings.
Ptolemy's geocentric model was satisfactory for the entire civilized world
known to the Romans and Greeks due to four factors:
1) It fit well with the predominant religious views. Beyond mythology, Judaism
and Christianity were quite popular. Both held to a Biblical view which places
man as the center of God's creation, and in the center of His attention. A geocentric
model would satisfy priest and rabbi.
2) It fit well with basic observation. Afterall, one only need look up at
the passage of the sun and moon. Clearly they are moving and we are not. If
we were moving or spinning, wouldn't we feel the motion and be dizzy?
3) It fit well with the basic philosophy that mankind holds ... we are the
center of our universe. Every high school student believes this to be true,
and it makes simple sense to see the universe act within the constructs of our
4) The mathematics were so detailed and complicated that none could understand
it. Why argue with such beautiful work. Ptolemy was really smart and his Almagast
very lengthy, so he must be right.
The geocentric model satisfied human observation, philosophy, and theology.
It was not questioned publicly for almost 1200 years. Ptolemy himself is not
responsible for the Dark Ages and the complete shutdown of science. But his
views gave religious leaders no reason to accept any other notion. A drawing
of the Universe, as Ptolemy saw it, is found below, and with the perfection
seen in the orbital paths, it becomes apparent to any historical student of
his day that this geocentric model fit the above-mentioned 4 criteria for widespread
After Ptolemy died, the science of Astronomy came to a halt, the Roman Empire
crumbled, and the Dark Ages ensued. The Church began a purge of all forms of
knowledge which might appear contradictory to a literal interpretation of the
Bible and thus books were burned in a frenzy. The vast Alexandria Library, with
many of the important scientific discoveries was burned and all its books lost.
Peace and prosperity continued to reign until about the end of the second century
A.D. Then a series of catastrophes dissolved the Roman Empire and all but destroyed
civilization itself. Decadent political and social systems collapsed. The exhaustion
of gold and silver coins, as the Spanish mines ran out of the precious minerals,
paralyzed commerce. A horrible pestilence, brought back from Asia my the military,
struck down the population at the rate of two thousand persons per day. Barbarian
tribes pressed in, conquering and devastating southern Europe.
The centuries that followed were a sad time for science. Deprived of comfort
in the world, people looked forward to solace in a better world hereafter, and
they turned away from the science of the past. Christianity, the major force
during the Middle Ages, brought with it a growing desire to reconcile science
in general and concepts of the universe in particular with the literal statements
of the Bible. Lactantius ridiculed the concept of a spherical earth. Most people
came to believe that the earth was flat, square, and supported by four pillars,
one at each corner. Under these conditions, contributions to science were rare.
Any unusual celestial event became a sign of prophetic nature, portending evil
or good for the earth. Superstition and fear were the motivating factors in
astronomical thought for many centuries. This aura of superstition, mysticism,
and magic obstructed the development of the sciences, especially astronomy and
The pseudo science of alchemy, bearing a relationship to chemistry similar to
that of astrology to astronomy, blossomed. There was widespread belief that
with the use of magic, potions, and incantations one could turn base metal into
silver or gold. Failure did not discourage the alchemists and magicians. From
time to time they even made, by accident, some useful chemical discovery. In
such an atmosphere, it is not surprising that astrology flourished. The idea
that God, through the stars, could influence mankind was not unacceptable to
the church fathers. And so, with full approval of the church, astrologers continued
to cast horoscopes.
Observational astronomy began again early in the sixteenth century. Belief in
a flat earth began to recede and in its place came an understanding of the universe
as visualized by Ptolemy and Aristotle.
The Greeks set the tone for an explanation of the Natural World. The Romans
were exercising control over the world with military strength and heavy taxation.
The developing Roman Catholic Church was spreading, despite efforts of Nero
and Diocletian to wipe out all followers of "the Way. It is my sincerest
opinion that issues of Church and Science are inseparable during the next 1400
years, and in order to really grasp the importance of the work of Copernicus,
you must first understand the effect of Church history, the rise and power of
the Papacy, and the impact of historical monarchs, or Roman Emperors who struggled
with or against each other for control of the people. Please
move next to a look at this history by clicking on Martin
Luther, or return to the Introduction
for this History Unit, the Syllabus,
or the Home page.
Do not forget to send in your responses to the questions
from the first half of this history unit. They can be found in the Assignments
folder under the heading Ancient
*** While the Greeks encouraged people to see the Earth as being spherical,
there were still many people who insisted that it was flat. There is even a
society today devoted to disproving the "Spherical Earth Hypothesis."
If you do not wish to accept the opinion of the Greeks, or the photographs of
astronauts and satellites, and desire instead to believe the Earth to be flat,
then click on Flat
Earth Society to see their website, information on membership, and reasons
why their view is correct in their opinion :) ***
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