Even stars do not live forever. They move through different phases, from birth to death, which can be seen by their physical status.
Over 2000 stars are visible on clear nights. Greek scholars around 500 BC still believed them to be burning objects suspended in the sky.
All stars are hot balls of gas that radiate energy. However, they can have very different characteristics. Their sizes alone range from twenty kilometers in diameter to 2.5 thousand times the diameter of the sun. There are also great differences in luminosity as well as in density.
The temperature of a star can be determined by its apparent color. Red stars, with a surface temperature of less than 4000┬░ Celsius are considered "cold". Yellow stars have temperatures between 5500 and 8000┬░ Celsius. White stars range from 8000 to 10,000┬░ Celsius in temperature and blue stars are the hottest, with temperatures of up to 20,000┬░ Celsius.
A special phenomenon is the collapse of a massive star, when it becomes a supernova at the end of its natural development.
Especially bright stars seem to form conspicuous figures in the sky, which are known as constellations.
