commentary on the Almagest, based on the title of Theon's commentary on the third book of Almagest, which reads "Commentary by Theon of Alexandria on Book III of Ptolemy's Almagest, edition revised by my daughter Hypatia, the philosopher", but, based on analysis of the titles of Theon's other commentaries and similar titles from the time period, scholars have concluded that Hypatia corrected, not her father's commentary, but the text of Almagest itself. Her contribution is thought to be an improved method for the long division algorithms needed for astronomical computation. The Ptolemaic model of the universe was geocentric, meaning it taught that the sun revolved around the earth. In the Almagest, Ptolemy proposed a division problem for calculating the number of degrees swept out by the sun in a single day as it orbits the earth. In his early commentary, Theon had tried to improve upon Ptolemy's division calculation. In the text edited by Hypatia, a tabular method is detailed. This tabular method might be the "astronomical table" which historic sources attribute to Hypatia. Classicist Alan Cameron additionally states that it is possible Hypatia may have edited, not only Book III, but all nine extant books of the Almagest. Independent writings Hypatia wrote a commentary on Diophantus's thirteen-volume Arithmetica, which had been written sometime around the year 250 AD. It set out more than 100 mathematical problems, for which solutions are proposed using algebra. For centuries, scholars believed that this commentary had been lost. Only volumes one through six of the Arithmetica have survived in the original Greek, but at least four additional volumes have been preserved in an Arabic translation produced around the year 860. The Arabic text contains numerous expansions not found in the Greek text, including verifications of Diophantus's examples and additional problems. Cameron states that the most likely source of the additional material is Hypatia herself, since Hypatia is the only ancient writer known to have written a commentary on the Arithmetica and the additions appear to follow the same methods used by her father Theon. The first person to deduce that the additional material in the Arabic manuscripts came from Hypatia was the nineteenth-century scholar Paul Tannery. In 1885, Sir Thomas Heath published the first English translation of the surviving portion of the Arithmetica. Heath argued that surviving text of Arithmetica is actually a school edition produced by Hypatia to aid her students. According to