Happy equinox! The day and night are roughly equal today. However, that’s isn’t the true definition of an equinox. The actual equinox is the instant the earth’s rotational axis is perpendicular to a line connecting the center of the Earth to the sun. In the June solstice, the tilt of the earth’s axis leans the northern hemisphere the most towards the sun. The December solstice leans the southern hemisphere towards the sun. This lean affects both how much heat per square area a hemisphere gets and how long the days are.
An astronomical definition would be:
An equinox is an event in which a planet’s subsolar point passes through its equator.National Geographic
Ah… but there are two equinoxes. The September equinox and the March equinox. “Equinox” is derived from the Latin “aequi” (equal) and “noct” (night). It is somewhat inaccurate to refer to them as fall and spring equinoxes because our fall is Australia’s spring. They are better identified by their months if you are uncertain of your reader’s home hemisphere.
While much of the country enjoys cooler weather and the changing of the colors, In my neck of the planet, it hit 102 and we had a heat advisory, yet already I am seeing the earliest preparations for the Christmas holiday. That saddens me greatly.
The pumpkin patches are being harvested and soon we’ll be celebrating the US version of Día de los Muertos. Beyond that, there will be the Thanksgiving late harvest celebration. Fall will end with the December solstice, also known as Yule.
But is it fall or is it autumn? About 30% of Americans use autumn. Fall derives from the English phrase “the fall of leaves.” Autumn derives from the French “autompne” which in turn was derived from the Latin term for harvest. (Another language gift from the Normans.)
You could call spring “Vernum,” as it does follow the vernal equinox, but that word seems to have been lost to us.