Spring Equinox: the phenomenon that marks the beginning of the season

The dates on which the seasons begin are not chosen at random: they are the days when certain astronomical phenomena occur. What marks the Beginning of spring and the spring equinox, which in the southern hemisphere always happens in September. Autumn also has its own equinox, in March here on the southern side of the planet. Summer and winter are marked by solstices, in December and June.

The simplest way to explain the equinox is this: it is the day when night and day are exactly the same length. The origin of the word already explains this, as it comes from the junction of the words equuswhich means “equal” in Latin” and noxwhich means “night” in the same language.

This happens because on the day of the equinox, the sun crosses the Celestial Equator at a given moment, which is the line that divides the planet into two hemispheres, the north and the south, but projected in the sky.

In the case of the September equinox, after that day the sun starts to shine longer in the southern hemisphere, which has longer days than nights. In the northern hemisphere, the opposite occurs: from September onwards, the nights are longer than the days.

The exact date of the beginning of spring changes from time to time because of this astronomical phenomenon. That’s because each year the equinox happens at a different time, and so the beginning of the season can sometimes be on the 23rd, as in 2019, and sometimes on the 22nd, as it was in 2018.

Solstices

If the equinox marks the days when day and night are of equal length, what marks the solstice? Well, winter and summer begin on solstice days. This means that the day summer begins is precisely when we have the longest day of the year and the shortest night. This usually happens on December 21st. The winter solstice is the longest night of the year and the shortest day. This usually happens on June 21st.