Once. In Autumn (stangely). Known as 'Fall' in the colonies.
3 Twice. On the Autumnal equinox and on the Vernal equinox.
The autumnal equinox is also known as the fall equinox and the September equinox. An example of a sentence using "autumnal equinox" is "This year's autumnal equinox falls on a full moon. "
There are two equinoxes (i.e. vernal/spring and autumnal/fall) every year.
The "Vernal Equinox" is the beginning of "Spring" and the end of "Winter". The Autumnal Equinox is the beginning of "Autumn" or "Fall" and the end of "Summer". In the Northern Hemisphere, the Vernal Equinox is in March and the Autumnal Equinox in September each year.
Equinox (autumnal or spring)
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).
There are two days each year when the day and night are of equal duration, known as the equinoxes. The vernal (spring) equinox occurs around March 21st, marking the beginning of spring in the Northern Hemisphere, while the autumnal equinox occurs around September 22nd, marking the beginning of autumn.
They would be the vernal equinox and the autumnal equinox.
The Equinox (Vernal & Autumnal) There are only two times of the year when the Earth's axis is tilted neither toward nor away from the sun, resulting in a "nearly" equal amount of daylight and darkness at all latitudes. These events are referred to as Equinoxes
The longest day and shortest night occurs on the summer solstice. The shortest day and longest night occurs on the winter solstice. Midway between these points (2x a year) are the equinox, where the day and night are of equal length.
An equinox is when the sun crosses the celestial equator, resulting in day and night being nearly equal lengths all over the world. There are two equinoxes each year: the vernal equinox in March and the autumnal equinox in September.
The Autumnal Equinox occurs this year on 22Sep2012 at approx 1400hr GMT