While stars do not contain the bulk of material in the Universe they are very important. Most of the chemical elements in the periodic table are synthesized in stars. The motion of stars reveals the gravitational potential in space on scales from solar systems to galaxies. A star is born from a gas-dust cloud, possibly together with a planetary system. It lives as long as it takes to consume its nuclear fuel and then it dies with a bang or slowly fades away returning most of stellar material back into space.
Stellar observations reveal the properties of stars, their environment and even the presence of planets. Common birth place and age. Theoretical models (such as depicted in the image on the left) predict physical conditions and dynamics in depths and on scales that cannot be reached by observations.