Science

Spring Equinox: Why is this year March 20 instead of March 21?

It’s been going on for two years in a row, and this will be the third. If in our school textbooks it was clear that spring arrives every March 21, why have the last three seasons of flowers entered the 20th? Is this an anomaly? A phenomenon produced by climate change, perhaps? No. It’s a totally normal situation because, despite what we were told at school, spring has a changing arc of dates that runs from 19 to 21 March. And whether it falls on one day or the other depends only on the path that our planet describes around the Sun.

While it is true that the seasons are a kind of “agreement” of humanity, they are not arbitrary. This 2019 we will receive the spring at exactly 22:58 Spanish time, according to the National Astronomical Observatory (OAN), belonging to the National Geographic Institute. And it will be at that moment because the center of the Sun, seen from the planet, crosses the celestial equator in its apparent movement towards the north. In addition, this equinox is special because it coincides for the first time in 19 years with the superlunar of March, also known as the “worm moon,” a phenomenon that will not be repeated until 2030.

When this happens, the duration of day and night practically coincide. Therefore, this circumstance is also called equinox, which in Latin is something like “equal night”, and also occurs in autumn. In fact, since the seasons are inverted between the hemispheres by the inclination of the Earth’s axis, while in the north we celebrate the entrance of spring, in southern latitudes they receive autumn. This season will last until next June 21 at 17.54 hours, at which time there will be the soslticio of summer and the arrival of the warmest period of the year in the northern hemisphere.

The key: fit leap years
And why this variation in dates? The way in which the duration of the Earth’s orbit around the Sun (known as the tropical year) fits into the leap year sequence of the calendar. In fact, in the 21st century we have seen in 2003 the later spring and in 2096 it will be the time when the date is the most advanced in the present century.

In fact, in contemporary history the date of the seasons has not always been the same. Until the end of the sixteenth century, it was the case that these seasons of the year were increasingly brought forward by the calendar, which had ten months instead of twelve. From this date onwards, two more months were added to adapt this peculiar calendar to the seasons of the year, which did not fit together. Those months were Januaries (January), dedicated to Janus, the god of two faces. And Febrarius (February), dedicated to Februs, the deity who forgave the faults committed throughout the year.

Is it necessary to change the time?
Already fully inserted in the season, and although we have been noticing it since the beginning of the year, it is from these dates that the days lengthen more quickly. At the latitudes of the peninsula, the sun rises in the mornings before the previous day and in the afternoon it sets afterwards. Thus, at the beginning of spring the time when the Sun is above the horizon increases by almost three minutes each day at the latitude of the Iberian Peninsula.

The light will be even more noticeable when we change the last Sunday in March, next 31, to summer time, advancing one hour our clocks (at 2 will be 1, which shortens by 60 minutes that day). However, the European Commission presented a proposal to put an end to the time changes during 2019. Initially this 31 March was to be the last time change to be made in the European Union, but the European Parliament has asked to delay until 2021 the elimination of the time changes proposed by the European Commission.

Member States must communicate by April 2020 at the latest whether they will keep summer time or winter time. If they opt for the first option, the last time change will take place in March 2021, while the clock will be changed for the last time in October 2021 in those countries that choose to remain in winter time. Despite the European Parliament’s request, the 28 will discuss this issue again next June.

We will therefore still have to keep changing the hands of the clock for at least two more years.

Venus, Saturn, Jupiter and Mars visible
According to the OAN, there will be no eclipse of the Sun or Moon during spring. The first full moon of spring will be on March 21, and the following 29 or 30 days later. Thus, there will be three more full moons this spring on April 19, May 18 and June 17.

As for the visibility of the planets, at dawn Venus, Saturn and Jupiter will be visible, which during the month of June will be visible all night, while at dusk Mars will be visible.

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