The sun rises at the edge of the worldGeology
For a long time, the inhabitants of Qaanaaq have persevered in complete darkness. Now, in mid-February, the moment they have been looking forward to for months has arrived. Despite the freezing cold of minus 35 degrees Celsius, they have gathered at midday. As the first rays of sunlight shine into their faces, the people sing a song in the old tradition and throw their hats into the air.
Qaanaaq is one of the northernmost settlements in the world. It lies at the very tip of Greenland, just south of the 78th parallel. About 600 people, most of them Inuit, live here – in complete darkness for almost four months of the year. In winter, the polar night prevails, the sun remains behind the horizon around the clock. In summer, however, it does not set for four months. It also only shines flatly, but at least the temperatures climb above freezing during these months. In between, there are months of twilight, when it is neither really day nor night. The seasons in Qaanaaq are not comparable to ours.
The mirror sun
Thomas Schuler has a similar problem to the Inuit: no sun shines on his farm for four months. However, he does not live high up in the north, but deep in the Black Forest, in Simonswald. There, the sun rises every day, even in winter, but it only makes a flat path across the sky. Too flat for the Schulers’ farm, which is surrounded by mountain ridges of the Upper Black Forest. In winter, these cast such long shadows that not a ray of sunlight reaches the farm all day. But the resourceful tinkerer knew how to help himself: He installed a large mirror on the opposite mountainside. Now at least a little sunlight shines through the window even in winter.
Polar Regions – Arctic and Antarctic
The largest ice surfaces on earth are around the North Pole and the South Pole. Because of their special location, the polar regions receive very little sunlight and solar heat, and the summers are particularly short there. That is why it is always extremely cold there – temperatures of up to minus 70 degrees Celsius prevail throughout the year. The cold has allowed huge masses of ice to form in the polar regions.
The Arctic ice around the North Pole covers a large part of the Arctic Ocean in winter. It then covers an area of several million square kilometres. For the most part, this is a layer of ice that floats on the sea. In addition, the Arctic ice covers the northern areas of Europe, Asia and North America.
In contrast, the South Pole is located on a continent, Antarctica. Antarctica is the coldest place on earth. Its land mass is almost completely buried under a shell of ice and snow up to 4 kilometres thick. Almost three quarters of the fresh water on Earth is stored in this ice.
Humans, animals and plants have adapted to life in the “eternal ice”. Polar bears or reindeer, for example, protect themselves against the cold with a layer of fat and thick fur. Only a few people inhabit the Antarctic, the Arctic is somewhat more densely populated. The best-known inhabitants of the Arctic are the Inuit in North America and Greenland, but there are also the Lapps in northern Scandinavia and indigenous peoples in northern Siberia. In the past, they lived there as nomads and moved around with dog sleds. Today they use snowmobiles and many of them live in cities.
Hardly anything grows in the ice deserts around the poles because of the great cold. The ground between the polar regions and the cold temperate zone is permanently frozen to great depths. This ground is therefore also called permafrost after the Latin word “permanere” for “to last”. It only thaws slightly a few months a year. Then particularly hardy plants such as mosses, lichens or dwarf shrubs can grow on it. This region around the polar regions is also called subpolar tundra.
The polar regions are the coldest areas on earth. It is also here that it is apparent that the Earth is heating up: for some years now, researchers have been observing that the ice masses of the Arctic and Antarctic are melting. The consequences of this warming cannot yet be precisely estimated. But it is already clear that many habitats are threatened by the melting of the poles.
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 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.
Why are there seasons?
We enjoy the first warm rays of sunshine in spring, look forward to visits to the swimming pool in summer and trudge through colourful leaves in autumn. In December at the latest, we take our thick jumpers out of the cupboard, because it can get quite cold in the winter months – and it usually snows too. The seasons influence our lives, but also those of plants and animals. But how do the seasons change?
The most striking difference between the seasons: It’s warm in summer, cold in winter. The heat comes mainly from the sun, so the difference between summer and winter must have something to do with the sun.
In fact, there are several reasons: In summer, the days are long and the nights short. In summer, the air and soil have plenty of time to warm up during the day and cool down only slightly during the short night. In winter it is the other way round: the sun only brings a little warmth for a short time, and the air and soil cool down during the long nights.
In addition, the warming rays of the sun are weaker in winter. Compared to summer, the sun is lower in the sky. The sun’s rays therefore hit the ground more flatly. This spreads the sunlight over a larger area, so that each individual spot on the ground receives less light and heat. In addition, the sun’s flat rays have to travel a longer distance through the atmosphere, and more energy is lost in the process.
In summer, on the other hand, the sun is high in the sky. The light rays hit the ground steeply and bring a lot of warmth with them.
But while we in the northern hemisphere enjoy the warm summer, in the southern hemisphere it is winter. Because whether the sun is high or low in the sky and whether the days are long or short depends on whether it is the northern or southern hemisphere that is tilted towards the sun.
Near the equator, the length of the day and the position of the sun change very little during the year, so that it is tropically hot there all year round.
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