Nicolaus Copernicus surviving primary documents on the early years of Copernicus's childhood and education. Copernicus biographers assume that Watzenrode first sent young Copernicus to St. John's School, at Toruń, where he himself had been a master. Later, according to Armitage, the boy attended the Cathedral School at Włocławek, up the Vistula River from Toruń, which prepared pupils for entrance to the University of Kraków, Watzenrode's alma mater in Poland's capital. In the winter semester of 1491–92 Copernicus, as "Nicolaus Nicolai de Thuronia", matriculated together with his brother Andrew at the University of Kraków (now Jagiellonian University). Copernicus began his studies in the
Nicolaus Copernicus that the earth orbited the sun. Further mathematical details of Aristarchus' heliocentric system were worked out around 150 BCE by the Hellenistic astronomer Seleucus of Seleucia. Though Aristarchus' original text has been lost, a reference in Archimedes' book "The Sand Reckoner" ("Archimedis Syracusani Arenarius & Dimensio Circuli") describes a work by Aristarchus in which he advanced the heliocentric model. Thomas Heath gives the following English translation of Archimedes' text: Copernicus cited Aristarchus of Samos in an early (unpublished) manuscript of "De Revolutionibus" (which still survives), though he removed the reference from his final published manuscript. Copernicus was probably aware that