News: Autumnal Equinox
At the autumnal equinox , the Sun appears to cross the celestial equator, from north to south; this marks the beginning of autumn in the Northern Hemisphere.
These two great circles meet at two points, one of which is the vernal equinox and the other the autumnal equinox.
In the southern hemisphere, the autumnal equinox corresponds to the center of the Sun crossing the celestial equator moving northward and occurs on the date of the northern vernal equinox.
The Autumnal Equinox signals the end of the summer months and the beginning of winter.
In the language of science, an equinox is either of two points on the celestial sphere where the ecliptic and the celestial equator intersect.
One of the two places in the sky where the ecliptic crosses the celestial equator; or one of the two times of the year when the Sun crosses these points.
When the Sun passes this point, on about 23 September each year, nights begin to grow longer than days, and continue to do so until the Winter Solstice in December.
The picture on the left shows the view from the solar system , and from on the surface of the earth.
In fact, the Sun is at the equator, so both halves of the Earth are getting about the same amount of sunlight.
For the rest of us, it’s one of two times a year when the Sun crosses the equator, and the day and night are of approximately equal length.
The exact date and time of the fall equinox, when the sun moves into the astrological sign of Libra, varies from year to year.
The upper panel shows that on an equinox , neither half of the Earth points directly towards the Sun.
The dates of maximum tilt of the Earth’s equator correspond to the summer solstice and winter solstice, and the dates of zero tilt to the vernal equinox and autumnal equinox.
At noontime in the Northern Hemisphere the sun appears high in the sky during summertime and low in the sky during winter.
The date when night and day are nearly of the same length and Sun crosses the celestial equator moving southward.
South of the equator, its name is less appropriate, since it corresponds to the beginning of summer, though for historical reasons the name autumnal tends to be used for the September equinox in both hemispheres.
Neither hemisphere gets more sunlight than the other, so both have similar seasons.
The vernal equinox, also known as “the first point of Aries,” is the point at which the Sun appears to cross the celestial equator from south to north.
Either of two moments in the year when the Sun is exactly above the Equator and day and night are of equal length all over Earth; also, either of two points in the sky where the ecliptic and the celestial equator intersect.
When a pole is angled towards the Sun, its hemisphere receives more hours of sunlight, and when a pole is turned away from the Sun, its hemisphere experiences long cold nights.
