The moon is the only natural satellite of the earth. The moon does not shine itself, but only reflects sunlight. There are four phases - periodically changing degrees of illumination of the Moon by the Sun. New Moon is a state when the Moon is not visible. The waxing moon is the period between the new moon and the full moon, during which the moon's illumination increases. Full Moon - a state when the Moon is fully illuminated. The waning moon is the period between the full moon and the new moon, during which the illumination of the moon decreases. Since the Moon is a spherical body, when it is illuminated from the side, a "sickle" (month, crescent, hump) appears.