A crescent moon is a phase of the moon that occurs when only a small part of its surface is illuminated by the Sun. This shape resembles a thin, curved sliver and can be seen shortly after the new moon or just before the full moon. The crescent moon can appear in two forms: the waxing crescent, which grows larger, and the waning crescent, which shrinks. Crescent moons are often visible in the evening or early morning sky. They are part of the lunar cycle, which lasts about 29.5 days, and is divided into different phases, including the new moon, first quarter, full moon, and last quarter.