midnight
She does not appear under these two conditions simultaneously , except at long intervals of time . It will be necessary , therefore , to wait for the moment when her passage in perigee shall coincide with that in the zenith . Now , by a fortunate circumstance , on the 4th of December in the ensuing year the moon _ will _ present these two conditions . At midnight she will be in perigee , that is , at her shortest distance from the earth , and at the same moment she will be crossing the zenith . On the _ fifth _ question , `` At what point in the heavens ought the cannon to be aimed ? '' _ Answer . _ -- The preceding remarks being admitted , the cannon ought to be pointed to the zenith of the place .