Metonic Cycle
  • 19 year cycle with which sequences of solar eclipses repeat. Meton of Athens found in 430BC that 235 lunar orbits take almost exactly 12 lunar years of 12 new moons and seven of 13 new moons take almost exactly 19 years, allowing lunar and solar calendars, which otherwise diverge heavily, to coincide after 19 years.

Not what you were looking for?