Life sentence for Galileo

In the trial against the mathematician and astronomer Galileo Galilei (68), the verdict has been reached. The judges of the Catholic Church agree: Galileo’s “Copernican world view” contradicts the Bible. Galileo’s claim that the earth revolves around the sun was declared false and not proven.

In the Roman Dominican monastery of Santa Maria, the professor of mathematics was already forced to abjure his teachings while kneeling before the guards of the Catholic Church. Instead of imprisonment, Galileo now faces life-long house arrest. His books may no longer be published with immediate effect.

Galileo had spent years observing the night sky for his research. To do this, he used the latest technical tool, the recently invented “telescope”. His observations led to only one conclusion: the Earth – like the other planets – orbits the Sun. The Church warned him several times to be careful with such claims. Nevertheless, the scientist had vehemently advocated this “Copernican world view”.

The publication of his book “Dialogo” was the straw that broke the camel’s back: Pope Urban VIII reacted in an offended manner, and so Galileo was put on trial in Rome. The Church continues to insist on a literal interpretation of the Holy Scriptures as long as there is no clear evidence to the contrary.

Copernicus forbidden

Along with the condemnation of Galileo Galilei, the Church also banned the teachings of the scientist Nicolaus Copernicus. His theory, published almost a hundred years ago, formed the basis for Galileo’s scientific work.

In 1543, the year of his death, the physician and dedicated amateur astronomer Nicolaus Copernicus had published the book “On the Turnings of the Celestial Circles”. In it, he contradicted the official opinion of the Church. He claimed that the earth was not the centre of the world, but a planet revolving around itself and the sun.

Copernicus must have suspected what these findings meant and feared the punishment of the Church. Only shortly before his death did he allow his book to be published. Without his knowledge, however, a clergyman added a preface. In it, the “Copernican world view” was only presented as a pure hypothesis and calculation aid, not as a proven assertion. Copernicus could not contradict it: He did not live to see the first publication of his book.

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 revolves 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).

What is a planet?

Perhaps some of you have noticed a particularly bright star in the morning or evening sky: Venus. After the sun and the moon, it is the brightest object in the sky. Because it shines so brightly, it is also called the “morning star” or “evening star” – much to the annoyance of astronomers: because Venus is not a star, but a planet!

The most important difference: a star glows by itself, a planet does not. Stars have an energy source inside them, so they glow hot and emit light. A planet, on the other hand, is cold and does not glow on its own. We can only see it when it is illuminated by a star. Then the surface of the planet spreads the light of the star in all directions.

Most planets belong to a star. This is because planets do not form alone, but together with a star. They then belong to this star and orbit it – like Earth and Venus, for example, which orbit the sun.

And why is Venus so easy to see, even though it only transmits the light of the sun? It’s because of its dense cloud cover, which reflects the sunlight particularly well. In addition, Venus is the closest celestial body to the Earth after the Moon: just 40 million kilometres – that’s a stone’s throw compared to the distances in space. Because it comes so close to the Earth and its clouds reflect a lot of light, we can see it well in the sky.

Venus is not the only planet, of course. Like Earth, it is one of the eight planets in our solar system. And the sun is not the only star with planets either. Since there are an unimaginable number of stars, the universe must be teeming with planets.

What is our solar system and how was it formed?

Earth is not alone in space: people have been observing the sun, moon and stars in the sky for a long time. In the process, they discovered early on that some stars move. These wandering stars were observed and their paths followed. But for a long time, their movements were not understood – until about five hundred years ago, when a man named Nicolaus Copernicus solved the mystery: the Earth and the “wandering stars” are actually planets, all orbiting the Sun at different distances.

Today we know eight planets. To remember their names in the right order, the first letters of the sentence “My father explains our night sky to me every Sunday” help. – or in short: M-V-E-M-J-S-U-N.

Mercury is the planet that orbits closest to the sun. Then come Venus, Earth and Mars. These four inner planets have a solid surface of rock and are still relatively close to the sun – only a few hundred million kilometres.

Further out, at a distance of about one to 4.5 billion kilometres from the Sun, orbit the outer planets: Jupiter, Saturn with its rings, Uranus and, on the very outside, Neptune. They consist of gas (mainly hydrogen and helium) and are much larger than the inner planets. Jupiter and Saturn are about ten times the size of the Earth, which is why they are also called the gas giants.

Finally, there are asteroids, comets and dust clouds that also orbit the sun. The Sun’s gravitational pull holds all these celestial bodies together, forcing them to fly in circles as if on a long leash. All of this together is called the solar system. The moons are also part of it – but they are held in place by the gravitational pull of the planets.

But why does the sun have planets at all? It has to do with how the sun was formed: a cloud of gas and dust pulled together by its own gravity and became a star. But not all the material in this cloud was “built up” in the star – about one percent remained. And when the sun then began to shine, the radiation pushed the remaining matter back out.

The light gases were pushed far outwards, while the heavier dust and rock fragments remained close to the Sun. In the course of time, the planets were formed from these dust and gas clouds. This is why the solar system has the gas planets on the outside, the rocky planets further in – including our Earth – and the Sun right in the middle. It contains 99% of the mass of the solar system and holds everything together with its gravity.

Why is the earth round?

What happens if you always go in the same direction? Do you eventually reach the edge of the world or is the world infinite?” More than 2300 years ago, the famous Greek scientist Aristotle was already sure: neither one nor the other. Because the earth is not flat like a disc, but a sphere – but why?

To understand this, you have to go back to the time when the earth was formed. The force that was responsible for this is gravity – all massive objects attract each other. This force made pieces of rock collide and combine to form a planet. And it gave the planet its shape. Because gravity works equally strongly in all directions.

Since the earth was hot and liquid at the beginning, the material was able to flow into the shape that gravity dictated. If a piece of earth material moved further out somewhere, it was attracted by the rest until the surface was smooth and the same force of gravity worked in all places. And since gravity is the same in all directions, the shape of a sphere automatically emerged – because only with a sphere are all points on its surface equidistant from the centre of gravity.

But if you take a close look at the shape of the Earth, you will see that it is not a perfect sphere: it is slightly flattened at its poles and somewhat bulbous at the equator.

This is due to the Earth’s rotation: in the course of 24 hours, the Earth rotates once around its axis. This rotation creates a force called centrifugal force. We know this from the chain carousel when we fly outwards on the swings. In the case of the Earth, the centrifugal force causes the rock masses to slide outwards a little from the axis of rotation, i.e. from the poles towards the equator. There, the diameter of the earth is about 41 kilometres larger than between the north and south poles.