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 several Kraków astronomers with whom he collaborated in 1515–30 in observing eclipses. Tycho Brahe would include a fragment from the "Commentariolus" in his own treatise, "Astronomiae instauratae progymnasmata", published in Prague in 1602, based on a manuscript that he had received from the Bohemian physician and astronomer Tadeáš Hájek, a friend of Rheticus. The "Commentariolus" would appear complete in print for the first time only in 1878. In 1510 or 1512 Copernicus moved to Frombork, a town to the northwest at the Vistula Lagoon on the Baltic Sea coast. There, in April 1512, he participated in the election of Fabian