Free entry to the Stone Age Party

It is 21 June, three o’clock in the morning. The car parks at Stonehenge are hopelessly overcrowded. Food stalls and hundreds of toilet blocks are set up. Around the gigantic boulders, thousands of Stone Age enthusiasts are celebrating their party of the year – the summer solstice. There is drumming and dancing, self-appointed druids blow their horns. At 5:58 a.m. sharp, the time has come: the sun rises. Despite the overcast sky, great jubilation breaks out. The longest day of the year can begin. Everyone is eagerly awaiting the moment when the first rays of sunlight fall through the northeast entrance onto the “altar stone” in the middle of the stone circles.

Stonehenge, the world-famous “hanging stones”, located 13 kilometres north of Salisbury in southern England, attract millions of tourists from all over the world every year. The solstice celebrations are particularly popular, with tens of thousands of pilgrims arriving every year. In 1985, riots broke out and the celebrations were banned. Since 1998, celebrations have been allowed again, but for security reasons with a large contingent of paramedics, police and monument protectors.

The mysterious stone circle

Stonehenge has been thoroughly researched – and yet remains incomprehensible. Here, almost one hundred stones, some up to seven metres high, are arranged in several circles. The oldest parts of Stonehenge were built almost 5,000 years ago. In the following one and a half thousand years, the site was expanded, rebuilt and finally abandoned several times.

But who put the stones there? And for what purpose? Was it a ritual place of worship? Or rather a kind of observatory and astronomical calendar with which druids could predict the summer and winter solstices?

We will probably never be able to answer these questions definitively. And that is probably part of the fascination of this mysterious place.

Why are our days different lengths?

In summer we enjoy long days and short nights, but in winter it gets dark already in the afternoon. And around the North and South Poles there are even areas where the sun does not rise or set for months. So day and night can be of different lengths – but why?

We experience day and night because the earth is a sphere that rotates: when our dwelling place rotates into the illuminated area, it becomes day; when it rotates out again, night.

On top of that, the earth’s axis is tilted: During half the year, the northern hemisphere is tilted towards the sun, during the other half, the southern hemisphere.

If you look at how the tilted globe is illuminated by the sun, you can see: The northern and southern hemispheres are not equally illuminated. When our northern hemisphere is tilted towards the sun, the illuminated area there is larger than in the southern hemisphere. As a result, the place where we live turns into the sunlight earlier and out again later. So our day is longer than in the southern hemisphere.

The longest day in our country is when the northern hemisphere is most tilted towards the sun. This is always the case on 21 June. In Stuttgart, for example, there are about sixteen hours between sunrise and sunset. After that, the days become shorter again, which is why it is called the summer solstice.

The other way round is when the northern hemisphere is tilted furthest away from the sun. This winter solstice happens exactly half an orbit (i.e. half a year) later, on 21 December. In Stuttgart, the sun can then only be seen for about eight hours.

Exactly halfway between the solstices are 21 March and 22 September. On these days, day and night last exactly the same length of time (namely twelve hours), which is why they are called equinoxes.

The closer you get to the equator, the smaller the differences become. And exactly at the equator, day and night always last twelve hours.

The situation is completely different around the North Pole: this is tilted towards the sun for half the year, so that it is bright there without interruption for half the year. The other half of the year, the North Pole is tilted backwards. Thus, a six-month “polar day” is followed by an equally long “polar night”. The area around the North Pole where there are days when the sun does not rise or set at all is called the polar circle. The same thing happens around the South Pole, but with the seasons reversed: If it is daytime at the North Pole, it is nighttime at the South Pole, and vice versa.

Why is there day and night?

We spend our lives in the rhythm of day and night: it gets light in the morning, we get up. During the day we go to school or work, meet friends, do sports. In the evening it gets dark, we go to bed, and during the night we sleep. The next morning, the same routine begins again, day after day, throughout our lives. The alternation of day and night is so natural for us that the question almost sounds surprising: Why is there actually day and night?

At first glance, the answer is quite easy: it becomes day because the sun rises. Then it moves in an arc across the sky, finally disappears behind the horizon and night falls. So you might think that day and night alternate because the sun wanders.

But this impression is deceptive: in reality, we humans live on a sphere that rotates: the earth. The sun stands still and illuminates the globe – but only one side at a time. It is bright there, and if our place of residence is on this side, it is daytime for us.

But because the earth rotates, this place keeps moving. To us, it looks as if the sun is moving across the sky. And when our place turns over the edge of the bright side, we can no longer see the sun: It sets and it becomes dark night. Fortunately, however, the earth continues to rotate, and so we also come back to the sunny side, it becomes light again and a new day begins. Once the earth has rotated on its own axis, a day – 24 hours – has passed for us.

And in which direction does the Earth rotate? From a spaceship, you could immediately see that the Earth rotates to the east. On the surface of the Earth, you have to think a bit: to us, it looks as if the sun is coming from the east in the morning. But in reality, we turn towards the sun in the morning, that is, towards the east.

This also means that the sun is already shining to the east of us. So it rises earlier in the east – and the further east you go, the earlier it rises: in Dresden, for example, the sun rises almost half an hour earlier than in Cologne. And if you call Germany in the morning from your holiday in Thailand, the person you are talking to will wake up from a deep sleep: there, the day starts six hours earlier. Finally, in New Zealand, almost exactly on the other side of the world, it is always day when it is night here – and vice versa.

Why is the sun at different heights in the sky?

On hot summer days you are happy to have a cool shade, but in winter you don’t want to stand in the shade and freeze. But the world is unfair: in summer, of all times, the shadows are short because the sun is high in the sky. And in winter the sun is so low that even small hills cast long shadows. But why does the sun actually stand at different heights in the sky?

In reality, the sun is always in the same place, at the centre of the solar system. Only from our point of view it looks as if the sun comes from different directions. This is because we live on a sphere.

How the light from the sun arrives on the globe depends on where you are standing on this globe. If you are standing exactly at the “belly”, i.e. the place that faces exactly towards the sun, the light rays hit the surface of the sphere at exactly the right angle. The sun is therefore exactly above you in the sky.

If you go north from there, the surface of the earth curves away from the sun. Therefore, the sun’s rays no longer strike at right angles, but at an angle, from the south. From the earth, the sun is then no longer exactly above you, but slightly to the south.

And the further north you go, the flatter the rays of light hit, i.e. the lower the sun is above the horizon. If, on the other hand, you go south from your “belly”, it is exactly the opposite: the sun seems to come from the north, and the further south you go, the flatter it is.

But that’s not all: because the Earth’s axis is tilted, our position in relation to the Sun changes in the course of a year. In summer, when the northern hemisphere of the earth is tilted towards the sun, we are closer to the “belly”. The sun’s rays therefore strike the earth at a steeper angle and the sun is higher in the sky. In winter, on the other hand, the northern hemisphere is tilted away from the sun and we are further away from the “belly”. The light then hits the earth at a flatter angle and the sun is lower in the sky.

In addition, the Earth also rotates, so there is a second movement every day: In the course of the day, the sun moves from east to west across the sky – and this more or less high above the horizon, depending on the season.