September 2019 equinox is taking place on 23th at 07:50 UTC. Happy autumn Northern Hemisphere, happy spring Southern Hemisphere.
The September equinox (or Southward equinox) is the moment when the Sun appears to cross the celestial equator, heading southward. Due to differences between the calendar year and the tropical year, the September equinox can occur at any time from September 21 to 24.
Above, If you were on the sun at the equinox instant you’d be gazing toward the hemisphere of Earth shown in this simulated image. Image credit Fourmilab.
At the equinox, the Sun as viewed from the Equator rises due east and sets due west. Before the Southward equinox, the Sun rises and sets more northerly, and afterwards, it rises and sets more southerly.
The equinox may be taken to mark the end of summer and the beginning of autumn (autumnal equinox) in the Northern Hemisphere, while marking the end of winter and the start of spring (vernal equinox) in the Southern Hemisphere.
Everyone along Earth’s equator on the day of the equinox, will experience the noonday sun more or less overhead.
Illumination of Earth by the Sun on the day of an equinox. Credit wikimedia
Diagram of the Earth’s seasons as seen from the north. Far right: December solstice. Credit wikimedia