The night sky has always fascinated mankind. For this reason, certain configurations of stars that resembled animals, mythological characters or geometrical shapes were given corresponding names. From this came the constellations, of which we now have 88 in total.
All stars are created by the contraction of a cloud of gas and dust. This takes place under the influence of its own gravity. If the interior is hot enough, thermonuclear reactions occur causing the star to shine. This releases enormous amounts of energy.
There are very different courses the life of a star can take. If it is a massive star, the fuel reserves can be exhausted in as little as 10 million years. Then a supernova, which is a great explosion, can occur. The remains are scattered far out into space. What is left is a neutron_star of an especially high density. Stars the size of the sun have a life span of about 10 billion years. When their fuel reserves are burned up, they expand to form red giants. They cast off their gas envelope, leaving only the core, a white dwarf.
Some stars appear brighter than others in the sky. This can be because of their distance, or else because of their size, density or luminosity. Some stars change at regular intervals. The Cepheids belong to this group. There are also many binary stars that revolve around a mutual center.
