Phases of the Moon introduces how the Moon appears to change shape during the lunar cycle and explains that these phases are caused by the positions of the Moon, Earth, and Sun. The video defines key astronomy vocabulary such as natural satellite, waxing, waning, crescent, gibbous, first quarter, third quarter, new moon, and full moon. It identifies all eight lunar phases in order, explains that the cycle repeats about every 29.5 days, and teaches a mnemonic device—DOC in the Northern Hemisphere and COD in the Southern Hemisphere—to help identify phases. With review questions and an observation activity, this instructional science video supports elementary Earth and space science curricula focused on lunar phases, patterns in the sky, and scientific observation.