See how the phases of Earth’s moon work, from the full moon to the new moon and everything in between in this SPACE.com infographic. The moon is illuminated by light from the sun, which observers on Earth see reflected off the lunar surface. As the moon moves around Earth, the amount of illumination it receives from the sun changes, creating the lunar phases. The moon completes a single lunar cycle in about one month.
Source Space.com: All about our solar system, outer space and exploration