This early mathematicians works were based on trigonometric ideas, or using triangles to find out distances on Earth and in Space. Many star charts were used to prove the geocentric (Earth centered) theory based on observations that lasted from March 26, 127 to February 2, 147. To increase the amount of data used this mathematician also used the star charts developed by the earlier mathematical astronomer Hipparchus. Theon of Smyrna was a Greek mathematical astronomer who was calles "Theon the Mathematician" by this person. This mathematician's work and the geocentric theory was not challenged until 1543 when Copernicus proved the heliocentric (Sun centered) rotation of the Universe.