What is the lunar limb?
The lunar limb is the Moon’s apparent edge as seen from the Earth.
Does the limb remain in the same position on the Moon’s disc?
Yes. The limb remains in more or less the same position on the Moon’s disc except for very minor shifts due to perturbations.
What is the terminator?
The terminator is the boundary between the day and night sides of the Moon.
Does the terminator remain stationary?
No. The terminator sweeps right across the Moon’s disc, once when the Moon is waxing (called morning terminator) and again when the Moon is waning (called evening terminator).
Why is the terminator important for studying features on the Moon’s surface?
The terminator does not appear as a smooth line, due to the unevenness of the Moon’s surface. At the morning terminator line when the Sun has just started rising, the peaks of the mountains which catch the first rays of the sun are brightly lit while the valleys are still in shadow. A study of the lights and shadows at the terminator therefore can provide a valuable insight into the topography of the lunar terrain.