A TWO-WEEK DAY
Any feature of the Moon will change appearance during the two weeks that sunlight falls on it—the lunar day for that area. A fascinating exercise is to follow the play of sunlight across a big crater such as Copernicus.
A day or two after First Quarter, as the Sun rises over Copernicus, the peaks of the rim turn into a ring of light. As dawn creeps inside, the light reveals terraces on the crater's walls and its central peaks— and finally a flat floor of lava.
At Full Moon, sunlight pours down on the crater, flattening the view of the terrain but revealing rays— streaks of pulverized rock that shot from the newborn crater in the first moments after the meteorite impact.
As the Sun descends from lunar noon, shadows return and Copernicus takes on form and shape once more.
At lunar sunset, the crater is completely hidden by shadows. Then, one fine evening you see a young Moon low in the west and can start preparing to watch the show again.