Ptolemy of Alexandria was the most influential astronomer of the
ancient world. The books and theories Ptolemy developed served as a major
basis for future astronomers. It was during the Renaissance period that
his work became thoroughly studied and revised.
Ptolemy collected all ancient knowledge of astronomy and geography
including it in his book Almagest around 140 A.D. It follows, he then
wrote a four volume astrological study known as the Tretrabiblos. Ptolemy
claimed that the scribes of Babylon had been instructed since 750 B.C to
keep detailed astronomical diaries. These diaries were written for seven
hundred years on clay tablets. The tablets depicted night-sky events along
with river level changes and weather phenomena. Modern archaeologists have
confirmed the claim by unearthing Babylonian tablets recording observations
of Mars and Venus from that time period.
Ptolemy used a method of consulting lists of lunar phases, and
planetary movements complied over many centuries to look for any
similarities or regular patterns. The patterns that were discovered could
then predict the next occurrence of such an event. Ptolemy eventually
devised an ancient form of nautical almanac or “ephemeris”. Mathematics
could now not only be used to predict but to demonstrate whether a
particular theory was correct or not.
Ptolemy developed several theories of his own contrary to the beliefs
of many other Greek astrologers at the time. He upheld that the “heavens”
consisted of bodies orbiting the earth in a celestial path – this idea was
supported for some time. Though his views were altered by the Renaissance
(the sun was now placed at the centre), orbital concepts remain in modern
astronomy. Ptolemy was familiar with a early type of astroblade. A
skeleton star map which could be rotated above a solid plate engraved with
day-curves and hour lines for a specific geographic latitude. Ptolemy
became the first person to locate places on the earth’s surface by latitude
Ptolemy often complained about the poor quality of Babylonian
planetary data. Eclipses and other lunar events were timed with water
clocks. Other phenomena were not always reported in the greatest
scientific detail and some accounts were exaggerated. Astronomers made a
several series of observations to reduce the effect of one individual
error. Little thought was given to formulating new methods of accurate and
scientific data recording.
Ptolemy carefully distinguishes between forecasts related only to the
sky and those connected to the human world. He states that it is possible
to read human fate in the stars. Strangely, Ptolemy, as did other
astrologers of that time period all agreed that the Dog Star was red.
Today the Dog Star is blue white. No modern theory of stellar evolution
can account for such a colour change.
Overall, Ptolemy made several significant contributions to astronomy.
The collection of ancient astronomy information in his books preserved many
early theories. Although incorrect, Ptolemy’s centre of the universe
theory influenced orbital thinking. The greatest achievement Ptolemy
conceived was his method of locating specific places using a sort of astro
blade. This astro-blade creation would not be generally used until 1540 due
to material limitations.