An Etymological Dictionary of Astronomy and Astrophysics

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فرهنگ ریشه‌شناختی اخترشناسی-اخترفیزیک

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physical libration
  هلازان ِ فیزیکی، رخگرد ِ ~  
halâzân-e fiziki, roxgard-e ~
Fr.: libration physique  

A real periodic variation in the rotation rate of a celestial object, as distinct from a → geometrical libration. In particular, slight oscillations in the → Moon’s rotation caused by the → gravitational attraction of the Earth on the → equatorial bulge of the Moon’s near side. The Moon’s physical libration is about 0.03° in longitude and about 0.04° in latitude.

See also: → physical; → libration.