päiväntasaajaan

päiväntasaajaan is the Finnish term for the point in the year when the day and night are of equal length. The word is derived from “päivä” (day), “tasa” (equal) and the suffix “ajaa” indicating an event or time. It refers to the astronomical phenomena known as the equinoxes. Two equinoxes occur each year: the vernal equinox around 20‑21 March, when the sun crosses the celestial equator from the southern to the northern hemisphere, and the autumnal equinox around 22‑23 September, when it crosses from north to south. At these moments the Sun’s rays strike the Earth’s equator directly, producing nearly equal daylight and darkness worldwide, though local weather and geographical factors can cause small variations.

The concept has been important in many cultures for timekeeping, agriculture, and religious observances. In Finland, the equinoxes are marked in various traditions. The vernal equinox is associated with spring festivals and the renewal of life, while the autumnal equinox can signal the beginning of harvest season. Calendars, especially in agrarian societies, use equinoxes as key reference points for planting and gathering. Modern scientific understanding utilises precise astronomic calculations to determine the exact dates and times of the equinoxes, which can be predicted accurately to within seconds. The equinoxes also serve as a reference for the astronomical coordinate system, defining the celestial equator and prime meridian of the sky, and are used by navigators and astronomers worldwide.