Discrepancies between Radar Data and the Lunar Ephemeris

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Science  24 May 1968:
Vol. 160, Issue 3830, pp. 876-878
DOI: 10.1126/science.160.3830.876


Precise measurements of the Doppler shift of radar waves reflected from Moon disclose unexpectedly large discrepancies—averaging about 0.6 centimeter per second—between the radial velocities and the predictions based on the Eckert-Brown lunar ephemeris. These residuals have a rapidly changing component corresponding to a relatively large, variable, and unexplained discrepancy in radial acceleration of about 10-4 centimeter per second, per second, in magnitude and about 1 day in period.

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