What is the equinox?

We explain what the equinox is, some of its characteristics and history. Also, what are their differences with the solstice.

1. What is the equinox?

It is called equinox to any of the two moments of a year in which the Sun is located on the equatorial plane of the Earth , reaching according to the point of view of an observer located in the Earth’s equator, its maximum point or zenith (at 90 ° with respect to the ground ).

This occurs twice a year, at the end of the months of March and September , depending on whether it is the spring or autumn equinox , respectively, and serves to formally mark the beginning of these seasons in each terrestrial hemisphere: in March is spring in the North and autumn in the South, and in September vice versa.

The term equinox comes from the Latin aequus nocte (“equal night”) , which refers to the fact that that day night and day have approximately the same duration throughout the world, given that the parallel of inclination of the Sun coincides with the equator In the middle of the planet.

The equinoxes are also used as a reference point in astronomy , and in many human cultures it has an important significance in the religious or cosmological tradition

2. Equinox and Solstice

If the equinox is the point at which the plane of the Sun coincides with the Earth’s equator, making day and night the same length and marking the transit from the hot to the cold season or vice versa (depending on the hemisphere), the solstices instead they are determined by the positioning of the Sun on the imaginary lines of the terrestrial tropics (Cancer and Capricorn, according to the constellations located in them) and thus producing the most extreme points of climate and temperature on the planet: winter and summer .

The solstices are, thus, the opposite and complementary degree of the equinoxes , in which the Sun transits instead the constellations of Aries and Libra. Solstices usually occur at the end of the months of June (summer solstice) and December (winter solstice) in the Northern Hemisphere, and vice versa in the Southern Hemisphere.