Cat's Eye Nebula

The Cat's Eye Nebula is a bright planetary nebula in Draco, formed when a dying star expelled its outer gas. Its nested shells, knots, and fast-moving structures make it unusually complex.

Planetary nebula: An expanding shell of gas ionized by the hot remnant of a dying low- or intermediate-mass star. The Cat's Eye is a detailed example of this late stage of stellar evolution.
Planetary nebula nucleus: The hot stellar remnant at the center of a planetary nebula. Its ultraviolet radiation illuminates the Cat's Eye's expelled material.
Stellar evolution: The sequence of physical changes a star undergoes over its lifetime. The Cat's Eye formed during the late evolution of its central star.
NGC 6543: The New General Catalogue designation for the Cat's Eye Nebula. This catalog entry is the nebula's standard astronomical identifier.
Stellar wind: A continuous outflow of charged particles from a star. Winds from the central star interact with older expelled gas to sculpt the nebula's shells.
White dwarf: A compact stellar remnant supported against gravity by electron degeneracy pressure. The central star is evolving toward the white-dwarf state.
Asymptotic giant branch: A late phase in the life of a low- or intermediate-mass star, marked by a cool, luminous envelope and strong mass loss. The progenitor star shed much of the material that now forms the nebula.
Draco: A constellation in the northern sky, winding around Ursa Minor. The Cat's Eye lies in this constellation.
Photoionization: The process by which light ejects electrons from atoms or molecules. Ultraviolet radiation from the hot central star makes the nebular gas glow.
Emission nebula: A cloud of ionized gas that emits light at characteristic wavelengths. The Cat's Eye's visible glow comes from emission by energized atoms in its gas.

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