The Mid-Autumn Festival, Chuseok, Tsukimi, a huge share of humanity's holidays are scheduled by a full moon, not a date.

Lunar and lunisolar calendars pin their festivals to phases, which is why these dates move against the Gregorian calendar every year. The eighth-month full moon is celebrated across East Asia with mooncakes, family gatherings and, in Japan, a formal evening of moon-viewing with no obligation beyond looking.