Metonic cycle
Moon-sun synchronization
The Metonic cycle is the approximately 19-year period after which the phases of the moon fall on the same dates in the solar calendar.
Greek astronomer Meton of Athens identified this pattern in 432 BCE, recognizing that 235 lunar months nearly equals 19 solar years.
The cycle underlies lunisolar calendars like the Hebrew and Chinese systems, which use it to determine leap months: Easter's date depends on calculations derived from the Metonic cycle. (Sometimes written lowercase as metonic cycle.)
Insertion between existing elements
- leap yearCalendar with added day
- lunar monthMoon's orbital period
- solar yearOne complete Earth orbit
- GregorianNamed for a pope
Julian · Hebrew calendar · Chinese calendar · chronology · almanac · epoch · era · festivals
Celestial body blocks another
- lunationMoon's orbital period
- synodicRelating to orbital alignments
- siderealOf the stars
- celestialOf the sky above
ecliptic · orbit · periodicity · precession · tropical · anomalistic · apogee · perigee
Distinct period in sequence
- full moonCompletely lit satellite phase
- new moonUnlit lunar phase
- crescentCurved sickle-like arc
- gibbousConvexly swollen shape
waning · waxing · quarter · lunation · harvest moon · blue moon · moonlight · tides
Greece's capital city
- BabylonianOf ancient Mesopotamian empire
- ancient GreeceClassical Mediterranean civilization
- observationAttentive watching or remark
- astronomersScientists studying celestial bodies
intercalation
Insertion between existing elements
- leap yearCalendar with added day
- lunar monthMoon's orbital period
- solar yearOne complete Earth orbit
Gregorian · Julian · Hebrew calendar · Chinese calendar · chronology · almanac · epoch · era · festivals · Passover
eclipse
Celestial body blocks another
celestial · ecliptic · orbit · periodicity · precession · tropical · anomalistic · apogee · perigee · equinox
phase
Distinct period in sequence
gibbous · waning · waxing · quarter · lunation · harvest moon · blue moon · moonlight · tides · lunar year
Athens
Greece's capital city
- BabylonianOf ancient Mesopotamian empire
- ancient GreeceClassical Mediterranean civilization
- observationAttentive watching or remark
- astrologyastrology, zodiac, horoscope, horoscopes, birth chart
- calendarscalendar, calendar day, calendar year, calendar month, lunar calendar
- calendar quirksleap day, leap year, intercalation, precession, Julian calendar
- lunar cyclesfull moon, new moon, crescent moon, half moon, waxing crescent
- time unitssecond, minute, hour, seconds, day
- church calendarAdvent, Easter Sunday, Lent, Christmas, Pentecost
Metonic cycleweek
Seven-day span
calendar day · fortnight · month · year · clock hour
cycle, bicycle, motorcycle, cycling, cycles, cyclic, cyclical, cyclist