Report on Astronomical Constants
نویسنده
چکیده
Recent progress in the determinations of astronomical constants is reviewed. First is the latest estimation of the general relativistic scale constants, LC , LG, and LB (Irwin and Fukushima, 1999). By reestimating the uncertainty, the value of the rst constant is given as LC = 1:480 826 867 4 10 8 1:4 10 . Also noted is the rigorous relation among these three, LB = LC +LG LCLG. Based on the latest determination of the geoidal potential W0 in the IAG 1999 Best Estimate of Geodetic Parmeters (Groten, 1999), LG and LB were reevaluated as LG = 6:969 290 09 10 10 6 10 18 and LB = 1:550 519 767 3 10 8 2:0 10 . Since LG is roughly related to W0, a proposal to x its numerical value is presented in order to remove the geophysical ambiguity in its evaluation in the future. In that case, LG becomes a de ning constant for the scale di erence between the geocentric and terrestrial coordinate systems. While LC and LB remain as a primary and derived constant, respectively. Next is the correction to the current precession constant, p. The recent estimates of p based on Very Long Baseline Interferometry (VLBI) observation seem to converge to a value close to 0:30 00/cy (Mathews et al., 2000; Petrov, 2000; Shirai and Fukushima, 2000; Vondr ak and Ron, 2000). Unfortunately this is signi cantly di erent from 0:34 00/cy, the latest value determined from the Lunar Laser Ranging (LLR) data (Chapront et al., 1999). The di erence is roughly ten times larger than the sum of their formal uncertainties. Since the cause of this di erence is not clear, we rst arranged the best estimates based on VLBI and LLR techniques, respectively, then took a simple mean of these two best estimates, and recommend it as the current best estimate. The value derived is p = 5 028:78 0:03 00/cy. Similar estimates were given for some other quantities related to the precession formula; namely the correction to the obliquity rate of the IAU 1976 precession formula (Lieske et al., 1977), "1 = ( 0:024 5 0:002 5) 00/cy, and the o sets of the Celestial Ephemeris Pole of the International Celestial Reference Ssystem, 0 sin "0 = ( 17:5 0:8) mas and "0 = ( 5:2 0:4) mas. As a result, the obliquity of the ecliptic at the epoch J2000.0 was estimated as "0 = 23 26021:00405 6 0:00000 5. The draft IAU 2000 File of Current Best Estimates of astronomical constants, that is to replace the 1994 version (Standish, 1995) or maybe even the formal IAU 1976 System
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