Aastaarvude

Aastaarvude (the genitive plural of aastaarv) refers to the numerical designation of calendar years, i.e., the year component in a date. In most modern contexts, year numbers are expressed as decimal digits. In the Gregorian calendar, years are counted with numerals such as 1999, 2020, 2025; contemporary notation typically uses four-digit year numbers for most years from 1000 onward. Some systems use two-digit years in informal contexts or legacy data, which can cause ambiguity about the century.

Historically, the concept encompasses earlier forms of year designation. In antiquity and the Middle Ages, years were often denoted by era names, regnal years, or Roman numerals. The Hindu-Arabic numeral system, which is standard today, gradually displaced older scripts. In linguistic usage, the genitive form "aastaarvude" would appear when describing properties of year numbers, e.g., "aastaarvude kasutus" (use of year numbers).

In computing and data processing, year numbers are essential for sorting, dating, and time calculations. The concept includes handling leap years via the Gregorian rule and calendar transitions, such as the shift from Julian to Gregorian calendars in various regions. Year numbering is also presented with era indicators such as CE or AD and BCE or BC.