päiväntasauksia

Päiväntasauksia, known in English as equinoxes, are moments in time when the Sun crosses the celestial equator, meaning the solar disk is directly above the Earth's equator. This occurs twice each year, around March 20 or 21 and September 22 or 23. During the equinoxes, day and night are of approximately equal length across the globe, hence the name "equinox" derived from Latin words for "equal" and "night."

The Earth's axial tilt, which is approximately 23.5 degrees, is responsible for the seasons. During the equinoxes, neither the Northern nor the Southern Hemisphere is tilted either toward or away from the Sun. This results in a more even distribution of sunlight across both hemispheres. In the Northern Hemisphere, the March equinox marks the beginning of spring, while the September equinox signifies the start of autumn. Conversely, in the Southern Hemisphere, these seasons are reversed.

The exact timing of the equinoxes varies slightly from year to year due to the Earth's orbit and the Gregorian calendar system. Leap years help to synchronize the calendar with the Earth's astronomical year. For observers at the equator, the Sun appears directly overhead at noon on the day of the equinox. For those at the poles, the equinoxes mark the transition between periods of continuous daylight and continuous darkness.