Every year at the end of September, many people celebrate the Autumn Equinox Day, which is important not only for astronomers, but also for many people living in countries where the equinoxes are celebrated as holidays.
The autumnal equinox itself is an astronomical phenomenon associated with the crossing of the celestial equator by the Sun. The line of the light division of the planet into the parts illuminated and unlit by the Sun, called the terminator in astronomy, passes at the moment of equinox through the poles of the Earth and is perpendicular to the earth's equator. However, this can only be seen from space.
The date of the autumnal equinox in universal time falls on September 22 or 23 with the transition of the Sun from the Northern to the Southern Hemisphere. It is worth noting that south of the equator, this equinox is the spring equinox, while the vernal equinox, celebrated on March 20 in the Northern Hemisphere, is the autumn equinox in the Southern Hemisphere.