Star

A star is an enormous, luminous ball of plasma. Stars cluster together to form galaxies, and they dominate the visible universe. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth, together with daylight. Other stars are visible in the night sky, when they are not outshone by the Sun. A star shines because nuclear fusion in its core releases energy which traverses the stars internal and then radiates into outer space. Almost all elements heavier than hydrogen and helium were produced inside the cores of stars.

Astronomers can establish the mass, age, chemical composition and many other properties of a star by observing its spectrum, luminosity and motion through space. The total mass of a star is the principal determinant in its development and eventual fate. Other individuality of a star that is determined by its evolutionary history includes the diameter, rotation, movement and temperature. A plot of the temperature of many stars against their luminosities, known as a Hertzsprung-Russell diagram (H-R diagram), allows the current age and evolutionary state of a particular star to be determined.