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Science 1 August 1975:
Vol. 189. no. 4200, pp. 377 - 379
DOI: 10.1126/science.189.4200.377
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Articles

Past Orientation of the Lunar Spin Axis

William R. Ward 1

1 Center for Astrophysics, Harvard College Observatory and Smithsonian Astrophysical Observatory, Cambridge, Massachusetts 02138

The orientation of the lunar spin axis is traced from the early history of the earth-moon system to the present day. Tides raised on the earth by the moon have caused an expansion of the lunar orbit. Tides raised on the moon by the earth have de-spun the moon to synchronous rotation and driven its spin axis to a Cassini state—that is, in a coprecessing configuration, coplanar with the lunar orbit normal and the normal to the Laplacian plane (which is at present coincident with the normal to the ecliptic). This combination of events has resulted in a complex history for the lunar spin axis. For much of the period during which its orbital semimajor axis expanded between 30 and 40 earth radii, the obliquity of the moon was of order 25° to 50°. In fact, for a brief period the obliquity periodically attained a value as high as 77°; that is, the spin axis of the moon was only 13° from lying in its orbit plane.


THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
The Constitution and Structure of the Lunar Interior.
M. A. Wieczorek, B. L. Jolliff, A. Khan, M. E. Pritchard, B. P. Weiss, J. G. Williams, L. L. Hood, K. Righter, C. R. Neal, C. K. Shearer, et al. (2006)
Reviews in Mineralogy and Geochemistry 60, 221-364
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Topography of the Lunar Poles from Radar Interferometry: A Survey of Cold Trap Locations.
J. L. Margot, D. B. Campbell, R. F. Jurgens, and M. A. Slade (1999)
Science 284, 1658-1660
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Science. ISSN 0036-8075 (print), 1095-9203 (online)