midnight
But the moon is not always at her zenith when she reaches her perigee , which is once a month . She is only under the two conditions simultaneously at long intervals of time . This coincidence of perigee and zenith must be waited for . It happens fortunately that on December 4th of next year the moon will offer these two conditions ; at midnight she will be at her perigee and her zenith -- that is to say , at her shortest distance from the earth and at her zenith at the same time . `` Regarding question No. 5 , ` At what point in the heavens ought the cannon destined to hurl the projectile be aimed ? ' `` The preceding observations being admitted , the cannon ought to be aimed at the zenith of the place -LRB- the zenith is the spot situated vertically above the head of a spectator -RRB- , so that its range will be perpendicular to the plane of the horizon , and the projectile will pass the soonest beyond the range of terrestrial gravitation . But for the moon to reach the zenith of a place that place must not exceed in latitude the declination of the luminary -- in other words , it must be comprised between 0 ° and 28 ° of north or south latitude .