The vernal equinox (Vernal Equinox) is one of the most unique phenomena of nature, the essence of which, in scientific terms, is that “at the moment of equinox, the center of the Sun in its apparent movement along the ecliptic crosses the celestial equator.” In 2021, the spring equinox occurs on March 20.
Simply put, on this day, the Earth, rotating around its imaginary axis passing through the poles, while simultaneously moving around the Sun, is in such a position relative to the luminary that the sun's rays, carrying thermal energy, fall vertically on the equator. The sun moves from the southern hemisphere to the northern, and these days in all countries the day is almost equal to the night.
The spring and autumn equinoxes are considered the astronomical beginning of the respective seasons. The period of time between two equinoxes of the same name is called the tropical year. This year is today adopted for measuring time. There are approximately 365.2422 solar days in a tropical year. Because of this, the “approximately” equinox falls at different times of the day every year, moving forward by about 6 hours each year.