The planet Earth goes around our star, the Sun. Along its trajectory it passes through different distances with respect to it. When it reaches winter solstice it agrees that it is the shortest day and the longest night in the northern hemisphere and conversely in the southern hemisphere. This day is usually the December 21.

The winter solstice is a key event that marks a change in the natural and astronomical cycles. Starting from the winter solstice, in the northern hemisphere the nights begin to gradually shorten until the summer solstice in June.

What happens on the winter solstice?

Planet Earth reaches a point on its path where the Sun's rays strike the surface in the same way more oblique. This happens because the Earth is more inclined and the rays of the Sun hardly arrive perpendicularly. This causes fewer hours of sunlight, making it the shortest day of the year.

There is a bad idea in society in general about winter and summer according to the distance from the Earth to the Sun. It is understood that in summer it is hotter because the Earth is closer to the Sun and in winter it is colder because we we find further away. The path of the Earth around the Sun known as translation has an elliptical shape. On the spring and winter equinoxes, the Earth and the sun are at the same distance and on the same inclination. However, contrary to popular belief, the Earth is closer to the Sun in winter and further away in summer. How can it be then that we are colder in winter?

More than the position of the Earth with respect to the Sun, what influences the temperatures of the planet is the tilt with which the sun's rays hit the surface. In winter, at the solstice, the Earth is closest to the Sun, but its tilt is the highest in the Northern Hemisphere. That is why when the rays reach the earth's surface too inclined, the day is shorter and they are also weaker, so they do not heat the air as much and it is colder. In the southern hemisphere the opposite occurs. The rays hit the earth's surface in a more perpendicular and direct way so that for them, on December 21, summer begins. This situation of the Earth with respect to the Sun is called Perihelion.

On the other hand, in summer, the Earth is the furthest from the Sun in its entire trajectory. However, the inclination in the northern hemisphere makes the Sun's rays fall more perpendicular to the northern hemisphere and therefore it is warmer and the days are longer. This situation of the Earth with respect to the Sun is called Aphelion.

The winter solstice and culture

Throughout history, humans have celebrated the winter solstice. For some cultures the beginning of the year is December 21, coinciding with the onset of winter. Some Indo-European tribes also had festivities and rituals celebrating this day. The Romans celebrated Saturnalia, in honor of the homonymous god, and in subsequent days they paid homage to Mithras, in honor of the deity of light inherited from the Persians.

For the old traditions, the winter solstice represents the triumph of light against darkness. It is curious that this is the case when there are fewer hours of light in winter. However, this is so because from the winter solstice, the nights will be getting shorter and shorter and, therefore, the day will conquer the night.

The winter solstice also gives rise to many pagan festivals and rites. December 21 was celebrated in the Stonehenge since the Sun of the winter solstice aligns with the most important rocks of this monument. Today in Guatemala, the winter solstice is still celebrated through the ritual of the "Dance of the flyers". This dance consists of several people turning and dancing around a stake.

Goseck's circle

This circle is located in Germany in Saxony-Anhalt. It consists of a series of concentric rings that are nailed to the ground. It is estimated, according to archaeologists and historians around it 7.000 years old and that it was a scene of religious rituals and sacrifices. When they discovered it, they realized that there were two doors in the outer circle that were aligned with the winter solstice. That is why this suggests that its construction is due to a type of tribute to this date of the year.

Stonehenge, Great Britain

As we have previously mentioned, at Stonehenge the winter solstice was also celebrated thanks to the fact that the sun's rays align with the center altar and the sacrificial stone. This monument has about 5.000 years old and it is known in most of the world, being an important scene of rituals and astronomical observations for hundreds of years.

Newgrange, Ireland

There is a mound built hace 5.000 años covered by grass and lined with tunnels and canals in the north east of Ireland. Only on the day of the winter solstice does the Sun enter all the main rooms, which, according to some experts, indicates that the structure was built to commemorate this date.

Tulum, Mexico

On the eastern coast of Mexico, on the Yucatan Peninsula, Tulum is an ancient walled city that belonged to the Mayans. One of the buildings built there has a hole in the top that causes a flare effect when the day of the winter and summer solstice lines up with it. This building remained intact until the Mayan population fell with the arrival of the Spanish.

Why does the date of the winter solstice change from year to year?

The day that winter begins can occur on different dates, but always around the same days. The four dates on which it can occur is between December 20 and 23, both inclusive. This is due to the way in which the sequence of years fits according to the calendar we have. Depending on whether the year is a leap year or not and depending on the duration of each orbit of the Earth around the Sun. When the Earth makes an exact revolution around the Sun it is known as a tropic year.

Throughout our XNUMXst century, winter will begin in the days 20 22 of the December.

The winter solstice and climate change

Natural variations of the Earth's orbit, including those related to precession, redistribute, over extended periods of time, the incident solar radiation on the earth's surface.

Precession or ground roll is the spinning motion that the Earth's axis makes. The axis describes an imaginary circle in space and traces a revolution every 22.000 years. What does this have to do with global warming and climate change?

Over the past million years, these subtle variations in the Earth's axis have triggered significant decreases and increases in atmospheric concentrations of methane and carbon dioxide. It is known that greenhouse gas concentrations respond mainly to variations during the boreal hemisphere summer, that is, the time of year when the north pole points to the Sun.

Summer heat in the northern hemisphere reaches its maximum once every 22.000 years, when the northern summer coincides with the passage of the Earth by the point closest to the Sun and the northern hemisphere receives the most intense solar radiation.

On the contrary, the summer heat reaches its minimum 11.000 years later, once the earth's axis has turned to have the opposite orientation. The northern hemisphere will then have the minimum summer solar radiation because the Earth is in the position further away from the sun.

Methane and carbon dioxide concentrations rose and fell in harmony with changes in incident solar radiation on planet Earth throughout the last 250.000 years.

Every 11.000 years there is a winter solstice which is warmer since the incident solar radiation in the northern hemisphere is greater and, on the contrary, there is another winter solstice when completing the precession lap, which is colder since the rays of the Sun arrive more inclined. It is said that greenhouse gas concentrations are increasing naturally because we are approaching the time of precession in which the planet receives more solar radiation, but we know very well, that naturally, it would not increase as much It is because of human activities that global average temperatures are increasing so drastically.

With all this you can know a little more about the winter solstice and its relevance in the cultures of the world and throughout history.