Solar Calendars Based entirely on the Earth's revolution around the Sun (a tropical year, or roughly 365.24 days). The year is divided into 12 months, with leap days added to keep seasons consistent.

Gregorian Calendar: The standard international calendar used globally for civil purposes.

Julian Calendar: A precursor to the Gregorian calendar, still used by some Orthodox churches.

Persian (Solar Hijri) Calendar: The official calendar of Iran and Afghanistan, which is astronomically aligned with the spring equinox.2.

Lunar Calendars Based entirely on the phases of the Moon. A 12-month lunar year consists of roughly 354 days, meaning the months cycle backward through the solar seasons.

Islamic (Hijri) Calendar: A strictly lunar calendar used by Muslims worldwide to determine the timing of religious events and holidays.

Lunisolar CalendarsTrack both the Moon's phases and the Sun's position. Because lunar and solar years don't align perfectly, these systems periodically add an extra "leap" month to ensure seasons match up.

Hebrew Calendar: Determines the dates of Jewish holidays.Chinese Calendar: Used for traditional festivals (like Lunar New Year) and agriculture.

Other Notable Systems Ethiopian Calendar: Uses 13 months—12 months of 30 days and a 13th month of 5 or 6 days. Because of how it calculates the Annunciation of Jesus, it operates about 7 to 8 years behind the Gregorian calendar.

Buddhist Calendar: A lunisolar calendar used in several Southeast Asian countries, counting time from the Buddha's death.Mayan Calendar: An ancient Mesoamerican system that tracked sacred cycles (260 days) and solar cycles (365 days