Williams، James G. (1994). "Contribution to the Earth's Obliquity Rate, Precession, and Nutation". The Astronomical Journal. ج. 108: 711. Bibcode:1994AJ....108..711W. DOI:10.1086/117108.
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Williams، James G. (1994). "Contribution to the Earth's Obliquity Rate, Precession, and Nutation". The Astronomical Journal. ج. 108: 711. Bibcode:1994AJ....108..711W. DOI:10.1086/117108.