The 10 fields and concepts you'll meet in the response — defined in plain English, each with a real example value.
The shape of the illuminated portion of the Moon as seen from Earth, determined by the Moon's position relative to the Sun.
The eight primary phases are New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent. Each complete cycle takes approximately 29.5 days.
The percentage of the Moon's visible surface that is lit by the Sun (0-100%).
At New Moon, illumination is 0%. At Full Moon, it reaches 100%. The value increases during waxing phases and decreases during waning phases. Illumination percentage is useful for precise lunar calculations.
Exampleillumination: 87.5 (87.5% of visible surface lit)
The number of days elapsed since the most recent New Moon (0 to ~29.5 days).
Lunar age provides a precise measurement of position within the lunar cycle. Day 0 is New Moon, day 7.4 is First Quarter, day 14.8 is Full Moon, day 22.1 is Last Quarter. This is more precise than phase names for calculations.
ExamplelunarAge: 12.3 (12.3 days since New Moon)
A complete lunar cycle from one New Moon to the next, averaging 29.53 days.
Also called a synodic month. Lunation numbers (Brown Lunation Numbers) count cycles from a reference point (Lunation 1 began January 17, 1923). This standardized system helps astronomers and developers reference specific lunar cycles.
The phase of the lunar cycle when the illuminated portion of the Moon is increasing (New Moon to Full Moon).
During waxing phases, more of the Moon becomes visible each night. In the Northern Hemisphere, the right side illuminates first. Waxing phases include Waxing Crescent, First Quarter, and Waxing Gibbous.
The phase of the lunar cycle when the illuminated portion of the Moon is decreasing (Full Moon to New Moon).
During waning phases, less of the Moon is visible each night. In the Northern Hemisphere, illumination shrinks from the right. Waning phases include Waning Gibbous, Last Quarter, and Waning Crescent.
The lunar phase when the Moon's Earth-facing side is fully illuminated by the Sun (100% illumination).
Full Moons occur approximately every 29.5 days. Each month's Full Moon has traditional names (Harvest Moon, Wolf Moon, etc.). Full Moons are associated with stronger tides and, in folklore, with increased activity.
The lunar phase when the Moon is positioned between Earth and Sun, with its illuminated side facing away (0% illumination).
The Moon is not visible during New Moon (except during solar eclipses). This marks the beginning of a new lunation. New Moons are associated with spring tides and, in lunar gardening, with planting new seeds.
The distance between the centers of Earth and the Moon, varying from about 356,500 km to 406,700 km.
The Moon's orbit is elliptical, so distance varies. At perigee (closest), the Moon appears about 14% larger than at apogee (farthest). A "supermoon" is a Full Moon near perigee. Lunar distance affects tidal forces.
ExamplelunarDistance: 384400 (in kilometers)
The times when the Moon appears above or disappears below the horizon at a specific location.
Unlike sunrise/sunset, moonrise occurs about 50 minutes later each day due to the Moon's orbit. Some days have no moonrise or moonset at certain locations. These times are important for photography, fishing, and astronomical observation.
