• Dark, sinuous feature seen against the Sun’s surface: when seen at the Sun’s limb the same structures are seen as prominences. The prominences stand out bright against the dark of space but are cooler than the Sun’s photosphere, against which they look dark.
  • A threadlike fiber or structure, such as a thin wire.
  • A cathode, within a thermionic tube, which is directly connected to a source of current. Such a cathode, usually in the form of a wire or ribbon, becomes heated as current passes through it, and emits electrons when sufficiently heated. Also called filament cathode, filamentary cathode, filament-type cathode, or directly-heated cathode.
  • A filament (1), within an incandescent lamp, which emits light when heated. Such a filament is often made of tungsten or carbon.

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