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• n  (astronomy) a real or apparent slow oscillation of a moon or satellite
  the libration of the moon

• The cylinders would be built at the constantly moving "libration points," where the gravity of the earth and of the moon cancel each other out.
• In June 1982 they instituted a series of computer commands and gentle rocket bursts that swung the spacecraft out of its libration-point orbit into eccentric earth orbits.