Why Ptolemy is Important, or Why You Should Care

   So, poking around in Ptolemy's history, we find that he was both an Astronomer and Geographer as well as a Mathematician, living in Greece, under Roman rule, sometime in the stretch of 90-168 A.D.

   He is well known for his Geographic works, however, of most importance for this upcoming trial of Galileo, is his Almagest. This is the Arabic name for his Syntaxis Mathematica, his foremost work on Astronomy. It summarized the knowledge of his day and age, but also, and most importantly, gave the mathematics behind the phenomena, as is seen in this example above of the explanation of the earlier conclusions by Hipparchus in finding the distance of the Sun and Moon from Earth.


In Almagest, Ptolemy supports the Geocentric theory of the Universe, where the Earth is at the center, and the planets and starts orbit around it, as seen in this model to the right.

Because Ptolemy used the works of older Mathematicians in Almagest, one of the side-effects of his work becoming the preferred go-to text is that older texts fell out of use, and became outdated. Due to this, many of them stopped being recopied, and Ptolemy's Almagest is the only access that can be gained to many of the older works such as Hipparchus, one of the primary sources that Ptolemy used and expanded upon.


Also, one of the most useful parts of what he outlined, was the tables he included. These tables allowed for the computation of the position of planets either in the future or past, and opened up the art of Astronomy.