Spring Equinox 2021: Northern and Southern Hemisphere

As you already know, the Earth carries out a rotational movement on itself and a translational movement in orbit around the Sun. Rotation is responsible for the existence of days and nights, since only half a planet receives light from the star in every moment. Translation, on the other hand, is responsible for the stations existing. Or, more than translation, the fact that the earth’s axis of rotation is tilted a little more than 23º, so that the equator is not totally perpendicular to the Sun. .

This causes that, as the Earth orbits around the Sun , one hemisphere receives more light and heat than the other depending on the point of the orbit. The hemisphere that receives the highest solar incidence will be in summer or spring, and the other, in winter or autumn.

What does all this have to do with the equinox? It’s simple. Throughout a complete orbit to the Sun, that is to say, one year, there are two points in which the equator is perpendicular to this and, therefore, the day lasts practically the same as the night. These days are the equinoxes , and they are the ones that mark the beginning of spring and fall for astronomers.

In fact, the name equinox comes from Latin, which means “equal night” : aequinoctium. On this day, anyone on the line of the Earth’s equator would see the Sun rise exactly in the East and set exactly in the West.

Why is Spring Day celebrated?

Why and how is the Spring Day or vernal equinox celebrated in the world? Well, traditionally, the equinoxes have had great importance in many cultures, since they represented the end of winter and the beginning of the agricultural cycle , with the abundance that this meant. In the calendars of India and Persia, the spring equinox was also the starting day of the year, and today many cultures around the world celebrate the equinox in different ways:

• The Holi festival in Bhopal, India.
• Nowruz, Central Asia.
• The Songkran Water Festival, Thailand.
• The Rolling Cheese Festival, Gloucester, England.
• The White House Easter Egg Race, USA.
• The Floriade, Australia.
• El Cimburijada, Bosnia.
• The Spring Equinox Festival in Teotihuacán, Mexico.

Today we know all the astronomical details that define exactly when the equinox occurs . In ancient times, however, it was not so simple despite the advanced knowledge that was had in this matter, taking into account the resources at its disposal.

Julius Caesar established that the spring equinox occurred every March 25 in the entire northern hemisphere, when he established the Julian calendar in 46 BC. However, the small mismatch caused by the fact that the Julian year is a few minutes shorter than the Tropico gradually advanced the equinox in the calendar over the years, until the introduction of the Gregorian calendar by Pope Gregory XIII established it between March 19 and 21 of each year.

When is the spring equinox 2021 in the northern hemisphere

Given the nature of the equinoxes and the seasons, the spring and autumn equinoxes are reversed in both hemispheres. Because of this, there are those who prefer to call them the March equinox and the September equinox , in order to avoid confusion due to the change of hemisphere.

In the Northern Hemisphere, the 2021 spring equinox is considered to be on March 20 at 10:37 UTC.

When is the spring equinox 2021 in the southern hemisphere

In the southern hemisphere, the spring equinox will occur on September 22 at 19:21 UTC, coinciding with the autumn equinox in the northern hemisphere.

As a curiosity related to the solstices, we recommend this other article on Why do the seasons of the year exist .

We have just seen that the equinoxes correspond to the two points in the Earth’s solar orbit where the Sun falls perpendicular to the equator and day and night have almost the same duration. The solstices are, instead, the two points in which the axis of the earth is at its maximum inclination with respect to the Sun, and therefore they give rise to the longest day and night of the year.

These are the summer solstice, with the longest day of the year, and the winter solstice, with the shortest day. The summer solstice in 2021 will occur on June 21 at 03:31 UTC in the Northern Hemisphere and on December 21 at 15:59 UTC in the Southern Hemisphere. The winter occurs on the same dates in the opposite hemisphere.

To learn more about it, we show here about the winter solstice in the northern and southern hemisphere , summer solstice in the northern hemisphere and southern and Autumn Equinox in the northern and southern hemisphere .