Napév

Napév is the Hungarian term for the solar year, the period required for the Earth to complete one orbit around the Sun in relation to the cycle of the seasons. The word combines nap, sun, and év, year. In astronomy, several year definitions exist; napév typically refers to the tropical year, the interval between successive vernal equinoxes, which is about 365.24219 days.

For comparison, the sidereal year measures Earth’s orbit relative to the fixed stars and lasts about 365.25636 days, while the anomalistic year—time between successive perihelion passages—lasts about 365.25964 days. The tropical year is shorter than the sidereal year because of the precession of the equinoxes, which slowly shifts the alignment of seasons with the calendar.

Civil calendars aim to approximate the tropical year. The Gregorian calendar has an average year length of 365.2425 days, achieved by the leap-year rule: every year divisible by 4 is a leap year, except that century years are not leap years unless divisible by 400. Over 400 years this yields 97 leap years and keeps the calendar in alignment with the seasons over long timescales.

Napév has practical significance in timekeeping, agriculture, navigation, and astronomical observations, where aligning calendar dates with seasonal changes matters. While the term napév is primarily used in Hungarian-language contexts, the concept corresponds to the widely used notion of the solar or tropical year in international astronomy and calendrics.