Although inaccurate and incorrect, Ptolemy's notion of epicycles became one of his most popular. Another big and popular idea, perhaps some of his most famous work, was his methods and formulas of predicting the positions of planets. The biggest break-through of his planetary system was that it fit observational data. This had never been done before.

Ptolemy also argued that Hipparchus' year of exactly 365.25 days was an inaccurate figure, and that it in fact was 1/300 of a day less than that. Although that difference seems insignificant, it makes a large difference in other calculations. Ptolemy was right in the sense that Hipparchus was wrong, but it was off by 1/128 of a day, not 1/300. This made many of Ptolemy's calculations incorrect.

By examining the equinoxes and solstices, he quite accurately figured the length of the seasons and the dates of solstices and equinoxes. On top of the motion of the sun, planets, and moon, Ptolemy also theorized on the stars. This included his theory that fixed stars maintained the same position relative to each other.

Ptolemy, unlike most astronomers before him, believed that the center of our earth was not the exact center, but very near it. He based this idea mostly on his observations of  displayed by what we know now as ellipses, or slightly ovular orbital paths. Almost all astronomers of that time, or even after for that matter, believed the heavens were perfect in every way. So Ptolemy influenced the notion that conformists, the church, and most astronomers were wrong, and this gave way to a new age of thinking.