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Ecliptic and equinoxes on the Celestial Sphere

The two equinoxes are the vernal equinox (around the 21st of March) and the autumnal equinox (around the 23rd of September). The former marks the beginning of spring and the latter of autumn in the northern hemisphere.

The seasons are reversed in the southern hemisphere.

The equinoxes occur when the Sun, during its apparent path around the Earth, crosses the disc of the equator projected out into space travelling northwards at the spring equinox and in a southerly direction at the autumn equinox.
At each one the number of daylight hours is the same at any point on the earth's surface.

The time at which the Sun forms the greatest angle to the equator – from both the North and the South – is called the solstice.

See also