June 15, 2021

Spring equinox: the change of season becomes official | Science

Spring equinox: the change of season becomes official | Science

This year the official start of the spring it is not early morning, in fact, we will have to greet it with a "Good evening!", because the beginning of the new season in the northern hemisphere will take place from 22.58 hours on this Wednesday, March 20 in Spain. In the northern half of the planet, the passage from winter to spring occurs with the spring equinox, the precise moment in which the duration of day and night practically coincide at any point on Earth. It is also the astronomical moment in which autumn begins in the southern hemisphere.

In theory it is the beginning of a time of change of time, of the longest days, of the flowering of the trees, of the allergies and of the change of time. But we must bear in mind that last month was the February with the highest temperatures of what we have of century, that the ski season has been reduced due to the lack of rainfall, that the drought is much more than a threat in most watersheds and that the meteorological perspectives indicate that everything will continue in a similar way with the arrival of spring.

The spring equinox it is the precise moment in which the Sun cuts the plane of the Equator, an instant that this year will take place on March 20 starting at 9:58 pm in universal time (one more hour in Spain). The explanation and understanding of this moment is simple: the inclination of the axis of rotation of the Earth is about 23.5º, and the displacement of the planet by its orbit around the Sun originates the seasons, with the solstices and equinoxes as the points of change.

From the dawn we will have before our eyes a great change that also occurs in the equinox: the Sun, that left until now towards the Southeast, will leave exactly in the East and will be in the afternoon just in the West, which will suppose that day and night lasts practically the same, which is the meaning of the term equinox, which comes from Latin aequinoctium ("Same night"). From this day, the light time in the afternoon will be even more noticeable and will increase after the Time change of the last Sunday of March.

The spring equinox It can occur, during the 21st century, on three different dates, between March 19 and 21. The earliest start will be the year 2096 and the latest start occurred in 2003. The variations from one year to the next are due to the way in which the sequence of years fits according to the calendar (some leap years, others not) with the duration of each orbit of the Earth around the Sun (duration known as tropical year).

The spring equinox was the beginning of the year in almost all the calendars of antiquity and continues to be in several calendars still in force as the Persian or the Indian. It was also on the Roman calendar, as the names of the months reveal: Martius, Aprilis, Maius, Iunius, Quintilis, Sextilis, Septembris, Octobris, Novembris Y Decembris.

The organization of the calendar was always a headache in humanity, and Julio César, surrounded by Egyptian astronomers, ordered a first and intelligent reorganization of the existing old sol-lunar calendars, introducing the leap years.

Throughout the spring Mars will be visible after sunset and at dawn you will see Venus, Saturn and Jupiter, which can also be seen at night at the end of the season.

The equinoxes, like the solstices, tell the calendar history and of the great astronomical events that are incorporated into our life and that we continue to celebrate, since the spring equinox, or vernal equinox, is possibly the most outstanding. This phenomenon marks the transition from winter to spring, symbolizing survival, the resurgence of life and the emergence of nature.


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