KEY TERMS

• • Nebula

    A nebula is a vast cloud of gas and dust in space, often light years wide, and usually illuminated by radiation from stars within or nearby. Nebulae are places where stars are born, as the gravitational collapse of some of their material forms new systems of stars and planets. Some nebulae are the remnants of stars that have reached the end of their lives – stars that have either thrown off their outer layers or exploded as supernovae.