Calendarssolar

Calendarssolar is a term used to describe calendar systems that are designed to keep their year length and date placement in close correspondence with the solar year, defined as the cycle of the Sun as observed from Earth. Such calendars aim to keep seasons on approximately the same dates from year to year, in contrast to lunar calendars that follow Moon phases and to lunisolar calendars that mix lunar months with solar alignment.

Most solar calendars assign a year length near 365 days and incorporate leap adjustments to restore alignment with the tropical year, which is about 365.2422 days. They typically divide the year into months, often with fixed day counts or a standard pattern of month lengths, and rely on leap years or leap days to compensate for the fractional day.

Examples include the Gregorian calendar, the most widely used civil solar calendar; the Iranian (Solar Hijri) calendar, which begins at the vernal equinox and uses a 365-day year with leap years that yield a closer alignment to the tropical year; and other regional solar calendars such as the Coptic and Ethiopian calendars, as well as various historical systems.

Challenges for solar calendars include maintaining long-term seasonal accuracy, cultural or religious requirements for fixed dates, and the complexity of leap-year rules. In modern use, solar calendars enable civil timekeeping, agricultural planning, and international synchronization.

See also: calendar, solar year, leap year, lunisolar calendar, Gregorian calendar, Solar Hijri calendar.