Full Moon. Image 8 of 15. Optical image of a full Moon fourteen days into its 28-day cycle. The Moon is full when its entire sunlit face is facing Earth. The phases of the Moon are due to it revealing different amounts of its sunlit face as it orbits Earth. The Moon is gravitationally locked to Earth, and always presents the same hemisphere to us. The dark grey areas are the lunar seas. They were formed early in the Moon's history by lava (molten rock) flowing into large impact craters and solidifying. The lighter areas are rocky highlands. Image taken on 16th June 2000. For a sequence showing the Moon throughout its cycle of phases, see images R340/596-610.