The word equinox comes from the Latin æquinoctium: the intersection of the terms æekus (equal) and nox (night). As its name implies, it determines the moment when the day is equal to the length of the night. This is a relatively rare phenomenon because it only occurs twice a year, in March and September.
A phenomenon associated with the sun, the earth and its tilted axis
The earth rotates around itself and around the sun at an inclination of about 23.5 degrees. Depending on its location in its orbit, it produces different radiations everywhere on the planet. Thus, between March and September, the days are long and hot in the northern hemisphere and cold and short in the southern hemisphere because the northern part of the Earth’s rotation axis is turned toward the sun. But the opposite happens between the months of September and March because the rotation of the southern part of the Earth is directed towards the sun.
Twice a year, the equinox puts everyone in agreement
Therefore, it is the inclination of the Earth relative to the Sun that we owe to the variety of seasons in different regions of the planet. But the equinoxes correspond to the only two days of the year when the two hemispheres are equidistant with respect to the sun. ! On these two dates, the Sun crosses the Earth’s equator: it rises almost exactly in the east and sets, 12 hours later, almost exactly in the west. And everyone has the same duration of sunshine. As a result, the equinoxes are punctuated by the periods of spring (in March) and autumn (in September). But what about the other seasons?
Illustration showing the relative position of the equinox and solstice in relation to the earth’s rotation and seasons/Wikimedia Commons
Winter solstice and equinox: what’s the difference?
And what is the coup in all this? On the contrary, they correspond to days when the disparity between the duration of the day and the duration of the night is greater. They occur in June and December and mark the beginning of summer and winter.
>> Read also: Do all planets have seasons?
