Waning crescent Moon. Image 15 of 15. Optical image of a waning (decreasing in apparent size) crescent Moon twenty-six 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. Image taken on 28th June 2000. For a sequence showing the Moon throughout its cycle of phases, see images R340/596-610.