The correct spelling of the word for a leap year, which has 366 days instead of 365, is intercalary year. The word is pronounced in-tur-KAY-luh-ree year, with primary stress on the second syllable. The phonetic transcription of the word is /ˌɪn.tərˈkeɪ.lər.i jɪr/. The word derives from the Latin word intercalare, meaning "to insert into the calendar." Intercalary years are necessary to account for the extra time it takes the Earth to orbit the Sun, approximately 365.2422 days.
An intercalary year, often referred to as a leap year, is a calendar year that is one day longer than a regular year, designed to maintain synchronization between the calendar year and the solar year. The addition of an extra day, called a leap day, usually occurs in February, making the month consist of 29 days instead of the usual 28. This adjustment compensates for the discrepancy between the duration of the Earth's orbit around the Sun (approximately 365.24 days) and the 365-day calendar year.
The concept of adding an extra day to the calendar dates back to ancient times, with the establishment of various leap year rules and systems throughout history. The adoption of the Gregorian calendar in 1582 standardized the practice of intercalary years in many countries. Under this system, any year divisible by 4 is a leap year, except for years that are divisible by 100 but not by 400. This exception prevents excessive accumulation of extra time and ensures a more accurate approximation of the solar year.
The purpose of an intercalary year is to align the calendar with the Earth's seasonal cycle, preventing a gradual shift and maintaining consistency over time. Without this adjustment, seasonal events, such as the equinoxes and solstices, would gradually occur on different dates, resulting in confusion and the potential disruption of various societal and agricultural activities that depend on accurate timekeeping.
The term "intercalary year" is derived from the Latin word "intercalāris", which means "inserted" or "interposed". The Latin word is a combination of "inter-" (meaning "between" or "among") and "calāris" (derived from "calāre", meaning "to announce" or "to proclaim"). In the context of intercalary year, it refers to the addition of an extra day or days (leap day) to the traditional calendar to keep it in alignment with the solar year.