Chinese firecracker against evil monster

The noise is supposed to drive away the monster of the year, Nian – for this reason, the Chinese welcomed the New Year with a bombastic fireworks display on the night of 23 January. The New Year in China is the most important festival of the year and is celebrated for a fortnight with many events.

In the Chinese calendar – unlike here – the year only begins on the first new moon of the year. This is because the traditional Chinese calendar divides the year into twelve lunar phases – the moon takes about 29.5 days from full moon to full moon. The New Year therefore falls on a different date each year, but always between 21 January and 19 February.

The New Year is the most important festival of the year for all Chinese around the world. But it no longer has any practical significance: since the founding of the Chinese Republic at the beginning of the 20th century, our Gregorian calendar, which is based on the sun, has also officially applied there. So the Chinese can celebrate the turn of the year twice.

Hair off at full moon

Cutting hair, washing clothes and dieting on a waning moon? Water flowers and fertilise fields when the moon is waxing? Many people believe in the influence of the moon on people. Lunar calendars are even really “in” again these days. They give tips on which activities are best to do or not to do at which phases of the moon.

Scientists can only shake their heads at such superstitions, because all research has shown that the phases of the moon have no influence on things like hair, flower growth or the human metabolism. So we can confidently go to the hairdresser whenever we want.

How are the phases of the moon created?

The moon is a funny thing: it changes shape all the time. Sometimes it’s round like a disc, sometimes it’s just a thin crescent – and sometimes we don’t see it at all. Why is that?

The moon (like the earth) does not shine by itself. We only see it because it is illuminated by the sun. To be more precise, we can only see the half of the moon’s sphere that faces the sun. The other half receives no light and remains dark.

What we see of this half changes over the course of a month as the moon circles the Earth once. When we see it from Earth with the Sun behind it, we look closely at the illuminated side and see the Moon fully illuminated, as a full circle.

When the moon moves further along its orbit, this changes: the sun’s rays now hit it from the left side as seen from us. The right edge is not illuminated, so it is not visible. The visible part of the moon continues to decrease on this part of the orbit. (“waning moon”)

Two weeks after the full moon, the moon is exactly in the direction of the sun, the side facing us is completely unlit – the moon seems to have disappeared. This point in time is called the “new moon”, because the moon does not remain permanently gone, of course, but continues to move and reappears anew in the sky.

This is because, little by little, some of the sun’s rays hit the side facing us again. Because the waxing moon is now on the other side of the earth than when it was waning, the sun’s rays now come from our right. At first we only see a narrow strip at the edge, but it quickly becomes wider. After a week, half of it is illuminated – we look closely at the light-shadow boundary from the side.

And another week later, we see the moon again with the sun behind it as a fully illuminated circle in the sky – and the process starts all over again.

How does the earth move?

Every morning we see the sun rise, move across the sky and set again in the evening. To us, it looks as if the sun is moving around the earth. Until the late Middle Ages, many people actually believed that the earth stood still in the middle of the universe and that everything revolved around it.

Today we know that it is the other way round: we experience day and night because the earth rotates. And the earth is neither still nor in the centre, but circles around the sun.

In the process, the sun’s gravitational pull holds the earth in place, as if on a long leash. To be more precise: a line almost 150 million kilometres long. This is the distance at which the Earth orbits the Sun.

We call the time it takes for the Earth to orbit around the Sun a year. In this time, the Earth covers a distance of about 940 million kilometres. That means it races through space at a speed of over 100000 km/h! (That’s almost thirty kilometres per second).

By the way, the Earth’s orbit is not exactly circular, but a very little bit elongated: At the beginning of January, the Earth is closest to the Sun. Half a year later, at the beginning of July, the distance is at its greatest. The Earth is then a few million kilometres further away from the Sun than in January. But this has nothing to do with the change of seasons: The difference is so small that the amount of sunlight hardly changes. (And besides, when the earth is closer to the sun in January, it is winter in the northern hemisphere).

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 the 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.

What is the moon?

It is the brightest celestial body in the night sky: the moon. On full moon nights, it shines so brightly that some people have trouble sleeping. It appears as big as the sun and the stars look like tiny points of light next to it.

But the impression is deceptive: in reality, the moon (diameter: 3474 km) is only about a quarter as big as the earth (12742 km) – and the sun (1.39 million km) is even four hundred times bigger. The moon only appears to be the same size because it is so close to us – the sun (distance to earth about 150 million km) is also about four hundred times further away than the moon. (384400 km, an aeroplane needs 18 days to cover this distance).

The bright light is also deceptive: unlike the sun, the moon does not shine by itself, but is illuminated by the sun. Part of this light is then reflected back from the moon’s surface and hits the earth. It is only because the moon is so close to us that enough light arrives on Earth to light up the night for us – at least when the moon does not seem to have disappeared without a trace.