Throughout a considerable portion of this period the great work of Copernicus was in manuscript, but it was not published until the year of his death.

The reasons for the delay are not very fully established.

Copernicus undoubtedly taught his system throughout the later decades of his life.

He himself tells us that he had even questioned whether it were not better for him to confine himself to such verbal teaching, following thus the example of Pythagoras.

Just as his life was drawing to a close, he decided to pursue the opposite course, and the first copy of his work is said to have been placed in his hands as he lay on his deathbed.
The violent opposition which the new system met from ecclesiastical sources led subsequent commentators to suppose that Copernicus had delayed publication of his work through fear of the church authorities.
There seems, however, to be no direct evidence for this opinion.