NATURAL satellite of the earth.It revolves around the earth in a slightly elliptical orbit EVERY 27 days,7 hours,43 min, 15sec (Sidereal month).As moon orbit the earth. It receives light from the sun and a CHANGING portion of its illuminated face that is visible from the Earth.These portions are the moon phases seen from the earth due to CHANGES in a relative position of the earth, moon, and the sun.Full Moon: LUNAR the phase when the Moon appears fully illuminated from Earth's perspective.Half Moon: The first quarter and the third quarter of the cycle of the moon (both often called a "half-moon") happen when the moon is at a 90-degree angle with respect to the earth and sun. New Moon: When the Moon and Sun have the same ecliptic longitude. At this phase, the lunar disk is not visible to the unaided eye, except when silhouetted during a solar eclipse.