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Precession and nutation from joint analysis of radio interferometric and lunar laser ranging observations24 years of Lunar Laser Ranging (LLR) observations and 16 years of Very Long Baseline Interferometry (VLBI) observations are combined in a global analysis to yield improved estimates of the Earth's precession and nutation. The correction to the International Astronomical Union (IAU) (1976) precession constant inferred from this joint VLBI/LLR analysis is -3.00 +/- 0.20 milliarcsec/yr (mas/yr). A significant obliquity rate correction of -0.20 +/- 0.08 mas/yr is also found. In all, 32 forced nutation coefficients are estimated. These coefficients confirm that the IAU (1980) nutation theory is in error by several mas. The estimated nutation coeficients are found to vary by as much as several tenths of mas, depending on the a priori nutation model used to analyze the VLBI and LLR data. Forced circular nutations derived from this analysis agree with the ZMOA-1990-2 nutation theory at the 0.2 mas level for the 18.6 yr terms, and at the 0.05 mas level for the other terms (periods less than or = 1 yr). A retrograde free core nutation with an amplitude of 0.20 mas is also detected. Its phase is found to be very sensitive to the precise value of the free core nutation period used in the solution. Separate analyses of four independent subsets of the LVBI data indicate no significant variations of the free core nutation since 1988. The pre-1988 estimates of the free core nutation are consistent with the post-1988 estimates but are not accurate enough to rule out possible variations of the free core nutation at these earlier epochs.
Document ID
19950053228
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Charlot, P.
(Jet Propulsion Laboratory, Pasadena, CA United States)
Sovers, O. J.
(Jet Propulsion Laboratory, Pasadena, CA United States)
Williams, J. G.
(Jet Propulsion Laboratory, Pasadena, CA United States)
Newhall, X. X.
(Jet Propulsion Laboratory, Pasadena, CA United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1995
Publication Information
Publication: The Astronomical Journal
Volume: 109
Issue: 1669
ISSN: 0004-6256
Subject Category
Astrophysics
Accession Number
95A84827
Distribution Limits
Public
Copyright
Other

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