For it is the duty of an astronomer to compose the history of the celestial motions through careful and skillful observation. then turning to the causes of these motions or hypotheses about them, he must conceive and devise, since he cannot in any way attain to the true causes, such hypotheses as, being assumed, enable the motions to be calculated correctly from the principles of geometry, for the future as well as for the past. the present author has performed both these duties excellently. for these hypotheses need not be true nor even probable; if they provide a calculus consistent with the observations, that alone is sufficient.” —copernicus, as quoted in the discoverers according to copernicus, what is the first duty of the astronomer? a. conceiving c. observation b. devising d. assuming