Why Are There 4 Seasons in a Year: Could Global Warming Make It 3 or 5?

We learn it since childhood, then we listen to it Poets and musicians Which is trying to lighten the coldness winter And with the return springWe are pleased with the arrival summer And he rose in gloom over the dead leaves. autumn.

But have you ever wondered why there are four seasons?

the time measurementAt the meeting Astronomy And the Arbitrariness

The terms we use to measure the passage of time are many and varied. Sometimes these choices are arbitrary: if we decide to divide the day into… 24 hours, We could have chosen something else. We decided to call. “week” For a period seven days, Thus after the creation of the world according to Biblical traditionBut in France, the Republican calendar, instituted on September 21, 1792 and abolished by Napoleon in 1806, consisted of a 10-day week: Bremidi, Dude, Tridi, Quartidi, Quintidi, Sextidi, Septidi, Octidi, Nonidi, and Decade.

But sometimes elections play a role Objective basis, Especially astronomical: and so on year It corresponds to the period of the Earth’s revolution around the Sun, and the month is related to the period of the Moon’s revolution around the Earth.

The modern understanding of this number is fundamental in nature astronomical. Let’s see. The Earth is driven by A. Double movement: a The path of the plane around the sun, communicate Sun’s pathand a Rotational movement on itself Around the south-north axis. It turns out that this axis, whose direction can be considered fixed as the Earth moves in its orbit, makes an angle of about 23 degrees with the perpendicular to the plane of the ecliptic. So, The Earth revolves around the Sun with the polar axis tilted relative to the ecliptic..

The result is that when viewed from a single point on the Earth, the Sun’s apparent path in the sky changes throughout the year. he The sun always rises in the east and always sets in the west. But in Summer rises higher in the sky than winter. As a result, Length of the day It gets longer as we enter summer and shorter as we enter winter.

The longest day of the year is called the summer solstice, which occurs on June 21, and the shortest day is called the winter solstice, which occurs on December 21. [NdeR ambas fechas en el hemisferio norte] (There may be a difference in the day due to leap years.) It is natural that between these two extreme moments there are two days in which the length of the night is equal to the length of the day: these are: Equinoxes (From Latin aequus, equal, and nox, night).

Spring equinox As the day gets longer (March 21 or 22 depending on the year), autumnal equinox When the period is shorter (September 22 or 23, depending on the year). It is also the day on which the sun passes vertically over the equator. The seasons are divided between these four specific times of the year, hence the number of seasons, simply put!

It is now appropriate to go back in time and note that this astrological interpretation was not always as prevalent as one might think. But phenomena do not depend on the knowledge we have about them (!), and their effects on Agricultural practices It was observed in all civilizations, It was even used in religious practices.

Thus, in Ancient Egypt, The Nile floods were decisive for CropsSo much so that the year was divided into Three seasons, each lasting four months: Akhet, flood period, Beret, receding waters, and Chimo, warm harvest period.

between the Assyrians And from the beginning of the second millennium as well Three seasons (Spring, Summer, Winter) is determined by the agricultural tasks to be performed. It is also curious that The first mention of December 25 as the day of Christ’s birth dates back to the year 336which recalls the traditional festival of that time. Invictus of the Sun (Invincible Sun) to celebrate the beginning of the lengthening of the days.

The use of agriculture as a marker of the passage of time may seem distant to us today, but we still retain a trace in the origin of the word station itself, which comes from the Latin word sationem, a noun that refers to “seed work”. More deliberately, we will also find this strong importance of agriculture in measuring time through the numerous sayings associated with the saint of the day, giving indications about crops, seeds and harvests. Thus we will say “To Santa Catalina, all woods take root,” indicating that November 25 is a date to remember to plant a tree.

But in recent decades, crops may have been negatively affected by the fact that climate change, because of Changes in the water cycleIn fact, a An increase of 1°C The average global temperature leads to a 7% increase in content Water vapor from the atmosphere. Temperate regions are also expected to become more dryThe driest areas desert And some tropical regions Uninhabitable.

Thus, some newspaper headlines were tempted to call, for example, “In the summer” also “Indian Summer” For this autumn It is characterized by heat And one drought It’s unprecedented, or even worth asking if we should be talking about it now. Five seasons Or if winter doesn’t arrive, it’s simply gone.

But still This is unlikely to change the naming of the stations: It is deeply rooted in our region cultureas evidenced by the world-famous work of the musician Vivaldi and the no less famous work of the painter Arcimboldo.

*Jacques Treiner is a physicist born in Switzerland in 1943. He completed his higher education at Pierre et Marie Curie University and the University of Paris-Sud d’Orsay. He has published about a hundred articles and worked in theoretical physics, especially in the field of quantum fluids. He was a professor at Pierre and Marie Curie University in Paris and published popular works such as How old is the Earth?

*This note was originally published in Conversation