Thursday 20th Mar 201416:55
On 20 March, the Sun will pass over the celestial equator on its northward journey, marking the beginning of spring in the northern hemisphere and of autumn in the southern hemisphere.
On this day, the Sun will be above the horizon for almost exactly twelve hours at all latitudes. The word equinox is derived from the fact that on this day, all places on Earth have equal hours of daylight and night time.
The point in the sky where the Sun lies at the moment of the March equinox (the vernal equinox) is traditionally called the first point of Aries, and is the definition of the zero point of right ascension.