What is a Nebula?
A nebula (from Latin:"mist"; pl. nebulae ) is an interstellar cloud of dust, hydrogen gas and plasma. It is the first stage of a star's cycle.
Originally nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older usage survive; for example, the Andromeda Galaxy was referred to as the Andromeda Nebula before galaxies were discovered by Edwin Hubble).
Many nebulae form from the gravitational collapse of diffuse gas in the interstellar medium. Some nebulae are formed as the result of supernova explosions.Other nebulae may form as planetary nebulae. This is the final stage of a low-mass star's life, like our own Sun. Planetary nebulae are so called because the first astronomers who observed these objects thought that the nebulae resembled the disks of planets, although they are not at all related to planets.
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