quantumaniac:What is a Nebula? In the early days of astronomy, the definition of Nebula was
quantumaniac: What is a Nebula? In the early days of astronomy, the definition of Nebula was rather broad - it really meant any astronomical object except comets or planets. However, nowadays the term means a large cloud made of gas and dust. Nebula are the breeding grounds of stars - most stars are thought to originate from these clouds. In Nebulae; gas, dust, and other materials combine to form a large mass, which then gravitationally attract further matter - and the being eventually garners enough matter to become a star. Once stars are formed from the material in a nebula, it is believed that the scattered remnants are what planets and other celestial objects (comets, etc.) are formed from. -- source link