The obvious rejoinder was to point out that the two lines were different. One line, one comet; two lines, two comets. Flamsteed, who was as painfully aware of the vagaries and limitations of observational astronomy as any man alive, had answered that comets didn't move along lines and never had; that astronomers had observed only short segments of comets' trajectories that might actually be relatively straight excerpts of vast curves. It was known, for example, that most of a hyperbola was practically indistinguishable from a straight line – so who was to say that the supposed two comets of 1680 might not have been one comet that had executed a sharp course-change while close to the Sun, and out of astronomers' view?