ΔT
出典: フリー百科事典『ウィキペディア（Wikipedia）』 (2022/11/04 17:57 UTC 版)
1955年以前の値
1955年以前の全ての ΔT の値は、日食や掩蔽による月の観測値に依存する。月の潮汐効果によって誘発される地球での摩擦によって失われた角運動量は、月に伝達され、角運動量を増加させ、そのモーメントアーム（地球からの距離）が増加する（約 +3.8 cm/年）。これは、ケプラーの法則により、月が地球の周りをより遅い速度で公転する原因となる。引用された ΔT の値は、この効果による月の加速度（実際には負の加速度である減速）が dn/dt = −26″/(cy2) であると仮定する。ここで、n は月の平均公転角運動である。これは、2002年時点で dn/dt の最良推定値である −25.858″/cy2±0.003″/cy2[12] に近いので、現在の値に適用される不確実性および平滑化を考慮して ΔT を再計算する必要はない。今日では、UTは、銀河系の電波源によって形成された慣性基準系に対する地球の観測された方向であり、恒星時と太陽時の採用された比によって修正されている。いくつかの観測所による測定は、国際地球回転・基準系事業(IERS)によって調整されている。
脚注
出典
参考文献
- McCarthy, D.D. & Seidelmann, P.K. TIME: From Earth Rotation to Atomic Physics. Weinheim: Wiley-VCH. (2009). ISBN 978-3-527-40780-4
- Morrison, L.V. & Stephenson, F. R. "Historical values of the Earth's clock error ΔT and the calculation of eclipses" (pdf, 862 KB), Journal for the History of Astronomy 35 (2004) 327–336.
- Stephenson, F.R. Historical Eclipses and Earth's Rotation. Cambridge University Press, 1997. ISBN 0-521-46194-4
- Stephenson, F. R. & Morrison, L.V. "Long-term fluctuations in the Earth's rotation: 700 BC to AD 1990". Philosophical Transactions of the Royal Society of London, Series A 351 (1995) 165-202. JSTOR link. Includes evidence that the 'growth' in Delta-T is being modified by an oscillation with a wavelength around 1500 years; if that is true, then during the next few centuries Delta-T values will increase more slowly than is envisaged.
外部リンク
- ΔＴ 暦Wiki、暦計算室、国立天文台
- IERS Rapid Service-Prediction Center Values for Delta T.
- Delta T webpage by Robert van Gent
- Delta T webpage by Felix Verbelen (archived from the original dead URL)
- Eclipse Predictions and Earth's Rotation by Fred Espenak
- Polynomial expressions for Delta T (ΔT)
- ^ IERS Rapid Service/Prediction Center (c. 1986). Historic Delta T and LOD. Source attributed data to McCarthy and Babcock (1986). Retrieved December 2009.
- ^ IERS Rapid Service/Prediction Center. Monthly determinations of Delta T. Retrieved May 2018.
- ^ ΔＴ ΔＴは不規則に変動する、暦Wiki、暦計算室、国立天文台
- ^ McCarthy & Seidelmann 2009, 88–89.
- ^ Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac, Nautical Almanac Offices of UK and US (1961), at pp. 9 and 71.
- ^ See G M Clemence's proposal of 1948, contained in his paper: "On the System of Astronomical Constants", Astronomical Journal (1948) vol.53 (6), issue #1170, pp 169–179; also G M Clemence (1971), "The Concept of Ephemeris Time", in Journal for the History of Astronomy v2 (1971), pp. 73–79 (giving details of the genesis and adoption of the ephemeris time proposal); also article Ephemeris time and references therein.
- ^ See Newcomb's Tables of the Sun (Washington, 1895), Introduction, I. Basis of the Tables, pp. 9 and 20, citing time units of Greenwich Mean Noon, Greenwich Mean Time, and mean solar day: and W de Sitter, on p. 38 of Bulletin of the Astronomical Institutes of the Netherlands, v4 (1927), pp.21–38, "On the secular accelerations and the fluctuations of the moon, the sun, Mercury and Venus", which refers to "the 'astronomical time', given by the earth's rotation, and used in all practical astronomical computations", and states that it "differs from the 'uniform' or 'Newtonian' time".
- ^ See p.612 in Explanatory Supplement to the Astronomical Almanac, ed. P K Seidelmann, 1992, confirming introduction of ET in the 1960 edition of the ephemerides.
- ^ See especially F R Stephenson (1997), and Stephenson & Morrison (1995), book and papers cited below.
- ^ A similar parabola is plotted on p. 54 of McCarthy & Seidelmann (2009).
- ^ :(1) In "The Physical Basis of the Leap Second", by D D McCarthy, C Hackman and R A Nelson, in Astronomical Journal, vol.136 (2008), pages 1906–1908, it is stated (page 1908), that "the SI second is equivalent to an older measure of the second of UT1, which was too small to start with and further, as the duration of the UT1 second increases, the discrepancy widens." :(2) In the late 1950s, the caesium standard was used to measure both the current mean length of the second of mean solar time (UT2) (result: 9192631830 cycles) and also the second of ephemeris time (ET) (result: 9192631770 ± 20 cycles), see "Time Scales", by L. Essen, in Metrologia, vol.4 (1968), pp.161–165, on p.162. As is well known, the 9192631770 figure was chosen for the SI second. L Essen in the same 1968 article (p.162) stated that this "seemed reasonable in view of the variations in UT2".
- ^ J.Chapront, M.Chapront-Touzé, G.Francou (2002): "A new determination of lunar orbital parameters, precession constant, and tidal acceleration from LLR measurements" (also in PDF). Astronomy & Astrophysics 387, 700–709.
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