solkalendere

Solkalendere, or solar calendars, are calendar systems whose reckoning is anchored to the tropical solar year and the progression of the seasons. They aim to keep calendar dates in step with the Sun’s position, so that, for example, spring or summer occurs in roughly the same months year after year.

Most solkalendere operate on a solar year of about 365.2422 days. To maintain alignment with the seasons, they insert intercalary days or months. The common civil solar calendar today is the Gregorian calendar, which uses 365 days in a common year and adds a leap day every four years, with century years skipped unless divisible by 400. Other solar calendars use different intercalation rules or astronomical methods to keep the year aligned with equinoxes and solstices.

In practice, solkalendere are used for civil timekeeping, agriculture, and administrative purposes. They contrast with lun calendars, which are based on lunar cycles, and with lunisolar calendars, which combine lunar months with a solar-digned framework to approximate the seasons.

Historical development: Ancient civil calendars in places such as Egypt and Mesopotamia sought to approximate the solar year for agricultural cycles. The Julian reform introduced a 365-day year with leap years, and the later Gregorian reform refined the leap-year rule to better approximate the tropical year.

Notable examples: the Gregorian calendar (the most widespread today), the Iranian (Jalali) calendar, and the Ethiopian calendar are all solar systems, but they differ in leap rules and month structure.