The Moon is one of the most fascinating objects in our sky. It rises and sets at different times and, depending on the phase it is in, looks like a bright circle sliced in half or a crescent soaring through the stars. Its cratered surface has remained unchanged for billions of years but what we see of it depends on where we are and when we look. The Moon is visible because its orbit and rotation are in sync with each other. This is known as tidal locking.
The side of the Moon that always faces us is called the near side and the other, the far side, is rarely seen. At the New Moon phase, only the dark side of the Moon is lit up and we can’t see the front face. At the first quarter, when the Moon is in its ascending node, we see a thin crescent of the near side, which is only partially illuminated. The next quarter, when the Moon is in its descending node, we only see the dark far side.
At the full Moon, both the near and far sides are illuminated by the Sun. The day side, which is facing the Earth, is called the ecliptic and the night side, which faces away from the ecliptic, is known as the anti-ecliptic.
At the last quarter, the terminator once again splits the lunar surface into two perfect halves of day and night. The astronomical term for this is the ‘waxing crescent’ phase. If the conditions were right, we might be able to see Earthshine (the faint rays of sunlight that are reflected from the Earth’s night side) shining on the terminator.