Many visitors come to see the historic medieval town centre. One of the main tourist attractions is the Krämerbrücke (the Merchants' Bridge). The bridge was built in its current form in 1472. It has buildings with shops and houses on it. People still live on it.
The city is well known for its festivals throughout the year. Two million people visit the Christmas markets each year.
Other important sites in the city include:
Magdeburg
Magdeburg (; ) is the capital of the state of Saxony-Anhalt, in Germany. The city covers an area of . About 236,000 people live there (2016).
A demonstration of air pressure (called the Magdeburg spheres) was done here by Otto von Guericke in 1656. Also, the 18th century composer Georg Philipp Telemann was born here.
Romance languages
The Romance languages (also sometimes called Romanic languages) are a language family in the Indo-European languages. They started from Vulgar Latin (in Latin, "vulgar" is the word for "common" and so "Vulgar Latin" means "Common Latin"). The most spoken Romance languages are Spanish, Portuguese, French, Italian and Romanian.
They are called "Romance languages" because they originate from Latin, the language spoken by the Western Roman Empire. Their grammatical inflection system has been simplified and lost most of the complex case structure of classical Latin.
The area that the Romance languages are spoken in Europe is mostly extent of the Western Roman Empire. The Greek language superseded Latin in the Eastern Roman Empire. Latin survived in Romania, whose language, Romanian, is a Romance language. In Moldova it is sometimes called Moldovan.
The Romance language family is one of the biggest in the world, and in total, there are almost a billion first and second language speakers.
Spanish is the most widely used Romance language, with Portuguese as the second and then French coming in at third.
Spanish is spoken mainly in Spain and Latin America. Portuguese is mostly used/spoken in Brazil, Portugal and parts of Africa. French is spoken in France, Belgium, Switzerland, Canada, and in some areas of Africa. Romanian is spoken in Romania and Moldova.
Stellar evolution
Stellar evolution is the study of how a star changes over time. Stars can change very much between when they are first created and when they run out of energy. Because stars can produce light and heat for millions or billions of years, scientists study stellar evolution by studying many different stars in different stages of their life.
The stages in a star's life are: nebula, main-sequence star, red giant and either white dwarf followed by black dwarf, neutron star or black hole.
A star starts its life as a cloud of dust and gas called a nebula. This is pulled together by gravity which causes it to heat up. It also starts to spin and to look like a ball. When it gets hot enough, it starts to release energy through nuclear fusion, changing hydrogen to helium. This makes it shine very brightly and become what astronomers think of as a main-sequence star. It may stay a main-sequence star, looking about the same, for billions of years.
Sooner or later, almost all of the hydrogen at the center has changed to helium. This causes the nuclear reaction in the middle of the star to stop and the center will start to get smaller due to the star's gravity. The layer of the star just outside the center will begin to change hydrogen to helium, releasing energy.
The outer layers of the star will get much, much bigger. The star will make much more light, sometimes as much as ten thousand times as much as it did at first. Since the surface of the star will get bigger, this energy will be spread out over a much larger area. Because of this, the temperature of the surface will go down and the color will change to red or orange. It will become a red giant. It can swallow up any planets that orbit around it.
Later, the red giant that was left over from a star like ours stops burning. A cloud of gas is given off and a smaller star called a white dwarf is left behind. After a really long time, the white dwarf cools down into a black dwarf.
But, when a big red giant explodes, the explosion is a lot larger and is called a supernova. Instead of a white dwarf, it leaves behind a much smaller, much denser ball called a neutron star. A neutron star is created because the force of gravity is so strong that the atoms left behind would not have any electrons orbiting the nucleus of the atoms. A teaspoon of that matter might weigh as much as the entire Earth.
A much bigger red giant leaves behind a black hole. A black hole is created because gravity is so strong that even the protons and neutrons collapse in on themselves. Even light can no longer escape a black hole. Since there is nothing we know of stronger than the force that holds atomic nuclei (the plural of 'nucleus') together, some physicists think that a black hole collapses all the way down to a mathematical point called a singularity.
Genetics
Genetics is a discipline of biology. It is the science of heredity. This includes the study of genes, and the inheritance of variation and traits of living organisms. In the laboratory, genetics proceeds by mating carefully selected organisms, and analysing their offspring. More informally, genetics is the study of how parents pass some of their characteristics to their children. It is an important part of biology, and gives the basic rules on which evolution acts.
The fact that living things inherit traits from their parents has been known since prehistoric times, and used to improve crop plants and animals through selective breeding. However, the modern science of genetics seeks to understand the process of inheritance. This began with the work of Gregor Mendel in the mid-nineteenth century. Although he did not know the physical basis for heredity, Mendel observed that organisms inherit traits via discrete units of inheritance, which are now called genes.
Living things are made of millions of tiny self-contained components called cells. Inside of each cell are long and complex molecules called deoxyribonucleic acid. DNA stores information that tells the cells how to create that living thing. Parts of this information that tell how to make one small part or characteristic of the living thing – red hair, or blue eyes, or a tendency to be tall – are known as genes.
Every cell in the same living thing has the same DNA, but only some of it is used in each cell. For instance, some genes that tell how to make parts of the liver are switched off in the brain. What genes are used can also change over time. For instance, a lot of genes are used by a child early in pregnancy that are not used later.
A person has two copies of each gene, one from their mother, and one from their father. There can be several types of a single gene, which give different instructions: one version might cause a person to have blue eyes, another might cause them to have brown. These different versions are known as "alleles" of the gene.
Since a living thing has two copies of each gene, it can have two different alleles of it at the same time. Often, one allele will be "dominant", meaning that the living thing looks and acts as if it had only that one allele. The unexpressed allele is called "recessive". In other cases, you end up with something in between the two possibilities. In that case, the two alleles are called "co-dominant".
Most of the characteristics that you can see in a living thing have multiple genes that influence them. And many genes have multiple effects on the body, because their function will not have the same effect in each tissue. The multiple effects of a single gene is called "pleiotropism". The whole set of genes is called the "genotype", and the total effect of genes on the body is called the "phenotype". These are key terms in genetics.