There are two equinoxes each year, in September and March, when the sun shines directly on the equator and the length of day and night is about the same.
Facing sides and stations
The seasons are opposite on both sides of the equator, so the equinox in September is also known as the autumnal equinox in the Northern Hemisphere, and is considered the first day of fall.
In the southern hemisphere, it is known as the vernal (spring) equinox and marks the first day of spring.
Local time and date of the equinox
September Equinox in Buenos Aires, Argentina is underway
Monday, September 23, 2019, 4:50 AM ART (Choose your city)
September Equinox in Coordinated Universal Time is underway
Monday, September 23, 2019 7:50 UTC
The sun crosses the celestial equator
The September equinox occurs the moment the Sun crosses the celestial equator, the imaginary line in the sky above the Earth's equator, from north to south. This happens on either September 22, 23 or 24 of each year.
The Earth's axis is tilted at an angle of approximately 23.4 ° relative to the ecliptic, the imaginary plane created by the Earth's path around the Sun.
On any other day of the year, the southern hemisphere or the northern hemisphere leans slightly towards the sun. But at the two equinoxes, the tilt of the Earth's axis is perpendicular to the sun's rays, as the illustrations show.
Why is it called the "equinox"?
At the equinox, night and day have almost the same length, 12 hours, all over the world. This is the reason why it is called "equinox", derived from Latin, which means "equal night". However, even if this is widely accepted, it is not entirely true. In reality, the equinoxes don't have exactly 12 hours of natural light.
Astronomical terms and definitions
Traditions and Folklore
In the Northern Hemisphere, the September equinox marks the beginning of fall (fall). Many cultures and religions celebrate holidays and festivals around the equinox.
A famous celebration of the ancient equinox was the Mayan sacrificial ritual of the main pyramid at Chichén Itzá, Mexico. The pyramid, known as El Castillo, has 4 staircases that run from the top to the bottom of the pyramid's faces, notorious for the bloody human sacrifices that used to take place here. The stairs are built at a carefully calculated angle that makes it look like a huge sun snake gliding down the stairs on the day of the equinox.