An object in the sky that sends out its own light, generated by nuclear reactions in its center. There are many billions of stars in our galaxy, the Milky Way.
- Our own sun is a medium-sized star.
- Each star has a definite lifetime and dies when it uses up its supply of fuel. (See black hole, neutron star, supernova, and white dwarf.)
- All chemical elements heavier than helium are created in the center of stars and are returned to space when the star dies.
- New stars are forming constantly.