Google it.
Or read what I have wrote:
An Autumnal equinox occurs on September 2.
It is a day when the day time approximately equals night time.
The Autumn equinox.
It is called equinox. Equinox happened 2 times per year on spring and autumn so called the name spring equinox and autumn equinox.
fall equinox partial equinox
The adjectives vernal and autumnal mean "of spring" and "of autumn (fall)" respectively. The equinox, when the day and night are even, occurs twice a year. Once in spring and once in autumn (fall) as we move from the extremes of the summer and winter solstices. Therefore we have a vernal equinox (in spring) and an autumnal equinox (in autumn/fall).
Autumn equinox and spring equinox I believe...
The word is "equinoctial" = equal day and night. It occurs twice a year, on the first day of Spring, and the first day of Autumn.
The autumnal equinox.
September
Autumn.It is regarded by some as the start of Autumn. There are different perspectives on when exactly Autumn starts, but for some it is the Autumnal equinox.
Spring and Autumn/Fall, for the Northern Hemisphere spring equinox is around March 21st and Autumn/Fall Equinox is around September 21st and for the Southern Hemisphere its the exact opposite.
The first day of autumn is called the autumnal equinox.
The equinox happens on Sept. 22. It marks the first day of autumn.