Lunar limb

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The lunar limb is the edge of the visible surface (disc) of the Moon as viewed from Earth.[1] Libration of the Moon, with its irregular surface, leads to small changes in its profile; this complicates the task of precisely calculating eclipse times and durations.[2] However, data from the mapping of the lunar surface allows astronomers to predict the lunar profile for any given time with a high degree of certainty.[3] The irregularity of the lunar limb is the cause of Baily's beads‍—‌collimated rays of sunlight that shine through in some places, and not in others, during a solar eclipse.

The contrast of a brightly illuminated limb against a black sky makes it a popular target when testing telescope and binocular optics.


  1. ^ "List of basic lunar features."
  2. ^ O'Byrne, Chris. "Lunar Limb Corrections. Archived 2008-01-13 at the Wayback Machine"
  3. ^ Watts, C. B. "The Marginal Zone of the Moon," Astron. Papers Amer. Ephem., 1963, 17, 1–951.