Although most modern calendar years have 365 days, a complete revolution around the Sun (one solar year) takes approximately 365 days, 5 hours, 48 minutes, and 46 seconds (or, for simplicity's sake, approximately 365 days and 6 hours, or 365.25 days).[5] An extra 23 hours, 15 minutes, and 4 seconds thus accumulates every four years (again, for simplicity's sake, approximately an extra 24 hours, or 1 day, every four years), requiring that an extra calendar day be added to align the calendar with the Sun's apparent position. Without the added day, in future years the seasons would occur later in the calendar, eventually leading to confusion about when to undertake activities dependent on weather, ecology, or hours of daylight.