The Chinese Lunar Calendar is a solilunar calendar, consisting of months corresponding exactly to lunar cycles and years which stay more-or-less in sync with seasonal years. The structure of the calendar depends on the exact times of certain astronomical events, principally dark moons and winter solstices. The solar calendar consists of a series of seasonal years which are divided into 24 "solar terms". The lunar calendar consists of a series of years which are divided into 12 or 13 lunar months. A solar year always begins at the (northern) winter solstice. A lunar month always begins on the day of a dark moon.