1. nebulaAstronomy
2. galaxyAstronomy, Obsolete term, See also 銀河
Wikipedia definition
3. NebulaA nebula is an interstellar cloud of dust, hydrogen, helium and other ionized gases. 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). Nebulae are often star-forming regions, such as in the Eagle Nebula.
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