What Types of Tools Did Ptolemy and Other Ancient Astronomers Use To Calculate the Position of the Planets?

We know of at least three tools Ptolemy used in his calculation of the position of the Sun, the planets, and the stars.

To measure the Sun’s position, he probably used a quadrant.

A quarter of a circle was ruled on a square board and a special line was attached to make sure it was held vertically.

There was a pivoting arm on the board with open sights. This arm was moved against the quadrant to determine the Sun’s height above the horizon.

A device called an armillary sphere was used for the planets. The sphere contained a series of circles.

These circles corresponded to the ancients’ view of the heavens as a series of circles surrounding Earth, each holding the planets as they revolved around Earth. The tool was used to give the planets a celestial latitude and longitude.

Ptolemy actually invented a tool to measure the position of the stars Ptolemy’s rules.

A stick was held vertically and a line attached to keep the stick straight. A pivoting arm with open sights was attached to one end. The other end had a pivoting board with movable pegs in it.

The pegs could be set at previously measured points to calculate the positions and movements of stars.