Nicolaus Copernicus

Nicolaus Copernicus, a canon of Frombork Cathedral who practised medicine and administration, worked for decades on his sun-centred model of the planets while circulating only a short outline. On the Revolutions of the Heavenly Spheres was finally printed in 1543, when he was 70; tradition says he saw a copy on his deathbed. The delay was partly caution, and partly the encouragement of his young follower Rheticus, who persuaded him to publish.