The Moon goes through a complete cycle of phases approximately every 29.5 days (a synodic month). Understanding these phases is essential for building apps that track lunar cycles, from gardening tools to fishing calendars.
The Eight Moon Phases
The lunar cycle consists of eight distinct phases: New Moon (0% illumination), Waxing Crescent (1-49%), First Quarter (50% right side), Waxing Gibbous (51-99%), Full Moon (100%), Waning Gibbous (99-51%), Last Quarter (50% left side), and Waning Crescent (49-1%). Each phase lasts roughly 3.7 days.
Waxing vs Waning
Waxing means the illuminated portion is growing (New Moon to Full Moon). Waning means it is shrinking (Full Moon to New Moon). In the Northern Hemisphere, the right side illuminates first during waxing. This is reversed in the Southern Hemisphere.
Lunar Age and Illumination
Lunar age is the number of days since the last New Moon (0-29.5). Illumination percentage indicates how much of the visible surface is lit by the Sun. These values are useful for precise calculations in gardening, fishing, and astronomical applications.
Lunation Number
Astronomers track lunar cycles using lunation numbers (also called Brown Lunation Numbers). Lunation 1 began on January 17, 1923. This standardized counting helps identify specific lunar cycles across history and into the future.