What started astronomy
What the stars tell us
Since time immemorial, people have wondered what the stars have to say to them and whether they can possibly give direct clues to the future. This is how astrology came about.
The modern natural sciences, on the other hand, do not look for connections between star constellations, dates of birth and personal fates - they want to learn something about the history of the universe and its laws of motion.
People's rhythm of life is still based on the rising and setting of the sun. Even if we turn night into day with modern light sources and, thanks to heating and air conditioning, are independent of seasonal fluctuations: Our biological clock is still based - without us having any influence on it - according to the course of the earth around the sun.
All cultures lived from assigning the rhythms of the sun and moon to the human rhythms of life and thus being able to plan important processes: sowing and harvesting, the migration of animals, the occurrence of ebb and flow and much more. The stars were an indispensable guide for navigating at sea.
It is actually not surprising that people to this day attribute a direct influence on fates and characters to both the so-called walking stars - including the sun, moon and planets - and the fixed stars and their figures, the zodiac signs, which are always to be found in the same place.
The focus is on people
Whether people used the sun, moon and stars to organize their time and calendar or were thinking about the mysteries of the inaccessible, distant stars: At first it seemed natural to them that the celestial bodies would move around them. The ideas of the ancient cultures of Greece, Egypt, China or Rome did not differ from the worldview of the medieval church.
The distance and inaccessibility on the one hand, the regular course of the celestial phenomena on the other hand made the firmament appear as the preferred place for the gods. Be it in the English Stonehenge, in the excavated site of Goseck an der Saale or in the Mayan cult sites: In the oldest observatories known to us, the early measurements of the position of the sun were combined with mythical ideas and rituals.
Already around 2500 years ago, Greek philosophers saw the earth as a sphere and thought about proportions and planetary movements. But the notion of a geocentric world with the earth at its center, as proclaimed by Aristotle, was never doubted and was theoretically consolidated by Claudius Ptolemy, who lived in Alexandria from around 100 to 170 AD. As the dogma of the Catholic Church, the geocentric view of the world lasted for centuries.
From the sky disc to the Hubble telescope
It is difficult to say since when measurements and representations of the celestial bodies have existed. In 1991 a wooden system was discovered near Goseck in Saxony-Anhalt, the orientation of which was precisely adapted to the highest and lowest sun positions. Its age is estimated at 10,000 years - that would be older than the one in Stonehenge, England.
A bronze disc with representations of the sun, moon and stars, which was found just 25 kilometers away in Nebra, is around 3500 years old. With their help, our ancestors could probably already do simple calculations.
With the invention and rapid development of the telescope in the 16th century, a new age of astronomy began and modern astronomy received tremendous impetus. What Galileo Galilei was able to see around 1600 with a telescope that he himself improved, anyone can find today with simple binoculars that magnify about ten times.
Even with such simple tools, however, it was possible to confirm the theory that the earth is not at the center of the solar system. The calculations and observations of Nikolaus Kopernikus, Tycho Brahe, Johannes Kepler and Galileo Galilei revolutionized the worldview: the sun was the center around which the earth moved like the other planets.
Since then the astronomical instruments have got better and better, the calculations so precise that space travel has begun and a telescope can even be installed in space. It bears the name of the English astronomer Edwin Hubble. At the same time, the development of the giant telescopes stationed on Earth continues.
Tubes and mirrors
Originally, telescopes consisted of a convex (collecting) and a concave (dispersing) lens. Johannes Kepler only used converging lenses in his improved design. The advantage: A target cross could be built into the beam path of this telescope, which made it much easier to determine the exact location of the observed objects.
However, all lens telescopes show imaging errors. Just a few years after the first Kepler telescopes were built, the first, technically unsatisfactory reflecting telescopes were also in use.
The decisive improvements were made by Isaac Newton from 1668 onwards. Now the reflector telescopes were a long way ahead of the lens telescopes in terms of image quality.
In the centuries that followed, ever more powerful telescopes with ever larger mirrors were built. The Keck telescopes on Mauna Kea in Hawaii with a mirror diameter of ten meters and the Gran Telescopio on the Canary Islands with 10.4 meters are the largest in the world today.
Such "giant eyes" have to be manufactured with sophisticated techniques and installed in locations with low air pollution, far away from interfering light sources. Air movements in the atmosphere distort the constellations, but a so-called "adaptive technique" corrects this flicker.
The "Hubble" stationed in space has a mirror diameter of only 2.4 meters, but it can work without the disturbing influence of the earth's atmosphere. Telescopes with even larger mirrors will follow.
The asteroid hunters
Sun, moon and stars inspire the imagination of romantics, meteorites and comets that of the prophets of the end of the world. Indeed, there is a threat to us from space: the asteroids, also known as planetoids. They move like the planets around the sun. 90 percent of the asteroids are located in the so-called asteroid belt between Mars and Jupiter.
But there are also asteroids whose orbits cross those of the earth. There have been catastrophic clashes in the past. The extinction of the dinosaurs is said to be the result of such an impact. Usually, the close approach of an asteroid is only noticed late - too late to avert a possible collision.
Nevertheless, the astronomers closely observe the dangerous hikers. In the future, one wants to predict collisions with a warning period of 30 years in order to be able to take countermeasures, for example by bombarding the asteroid with large rockets.
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