Waxing gibbous Moon. Image 6 of 15. Optical image of a waxing (increasing in apparent size) gibbous Moon eight days into its 28-day cycle. The phases of the Moon are due to it revealing different amounts of its sunlit face as it orbits the Earth. Dark grey lunar seas are seen, large impact craters filled with dark lava. Image taken on 10th June 2000. For a sequence showing the Moon throug- hout its cycle of phases, see images R340/596-610.