Reading of the chain of observations from Hipparchus and Ptolemy through al-Battani and Arzachel to Copernicus, I'm struck by the temporal scale of the shared undertaking. Hipparchus was working between about 147 and 127 BC. Ptolemy died around 168 AD. Al-Battani died in 929, Arzachel/Al-Zarqālī in 1087. Copernicus died in 1543.
During these long centuries the great orrery of the solar system spun against the stars according to its own laws. The equinoxes precessed at about a degree every 72 years. With the instruments available to Copernicus and his predecessors, getting a reasonably accurate value for that rate required going back to the work of observers working centuries before, a great Dead Astronomers Society sharing observations across hundreds of years.
Dead men talking: the awesome power of the written word. We take it too much for granted, so take a moment to appreciate the wonder of it.