Autumnal Equinox – Fall Equinox
Equinoxes are opposite on either side of the equator,
so the autumnal (fall) equinox in the Northern Hemisphere
is the spring (vernal) equinox
in the Southern Hemisphere and vice versa.
On the two equinoxes every year the Sun shines directly on the Equator
and the length of day and night is nearly equal – but not exactly.
The September equinox marks the moment the Sun crosses the celestial equator
– the imaginary line in the sky above the Earth’s equator –
from north to south and vice versa in March.