J/A+A/355/398 Celestial Ephemeris Origin definition (Capitaine+, 2000) ================================================================================ Definition of the Celestial Ephemeris Origin and of UT1 in the International Celestial Reference Frame. Capitaine N., Guinot B., McCarthy D.D. =2000A&A...355..398C ================================================================================ ADC_Keywords: Ephemerides ; Earth Keywords: astrometry - ephemerides - reference systems - time Abstract: The adoption of the International Celestial Reference System ICRS, and of the corresponding Frame, ICRF, by the 23rd General Assembly of the International Astronomical Union, calls for a redefinition of the departure point on the true equator. Several possibilities have been suggested. This paper considers the use of the non-rotating origin (Guinot, 1979, In: McCarthy D.D., Pilkington J.D. (eds.) Time and the Earth's Rotation. D. Reidel Pub. Co, p. 7). The ``Celestial Ephemeris Origin'' (CEO) is defined here as the non-rotating origin on the equator of the Celestial Ephemeris Pole (CEP). Developments valid at the microarcsecond, based on the best model for precession, nutation and pole offset at J2000.0 with respect to the pole of ICRF, are provided for computing the CEP coordinates and the position of the CEO. It is shown that an operational definition of UT1 based on the CEO leads to values which are insensitive at the microarcsecond level to future improvements of this model. Description: The tables contain the parameters of the development as functions of time t (expressed in centuries since J2000.0) of the Celestial Pole Coordinates X and Y, expressed in arcseconds, has the following form: X=-0.017130 + 2004.193319t - 0.4271605t^2^ - 0.1986210t^3^ -0.0000461t^4^ + 0.0000058t^5^ +{Sum on i}[(a_s,0_)_i_sin(ARGUMENT)+(a_c,0_)_i_cos(ARGUMENT)] +{Sum on i}[(a_s,1_)_i_.t.sin(ARGUMENT)+(a_c,1_)_i_.t.cos(ARGUMENT)] +{Sum on i}[(a_s,2_)_i_.t^2^.sin(ARGUMENT)+(a_c,2_)_i_.t^2^.cos(ARGUMENT)] Y=-0.005202 - 0.0219421t - 22.4072863t^2^ + 0.0018416t^3^ -0.0000037t^4^ + 0.0000019t^5^ +{Sum on i}[(b_c,0_)_i_cos(ARGUMENT)+(b_s,0_)_i_sin(ARGUMENT)] +{Sum on i}[(b_c,1_)_i_.t.cos(ARGUMENT)+(b_s,1)_i_.t.sin(ARGUMENT)] +{Sum on i}[(b_c,2_)_i_.t^2^.cos(ARGUMENT)+(b_s,2)_i_.t^2^.sin(ARGUMENT)] File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table1a.dat 97 269 Numerical Development of the coordinates X(t), Y(t) of the Celestial Ephemeris Pole in the ICRS consistent with the IERS 1996 Conventions and the IERS Annual report for 1997 (unit {mu}as) table1b.dat 82 112 Numerical Development of the planetary nutations in the coordinates X(t), Y(t) of the CEP in the ICRS consistent with the IERS 1996 Conventions and the IERS Annual report for 1997 (unit {mu}as) tables.tex 319 469 LaTeX version of the tables -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1a.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- i [1/269]+ Number i 5- 6 I2 --- l Mean anomaly of the Moon coefficient 8- 9 I2 --- l' Mean anomaly of the Sun coefficient 11- 12 I2 --- F L - Omega (L: Mean longitude of the Moon) coefficient 14- 15 I2 --- D Mean elongation from the Moon to the Sun coefficient 17 I1 --- Omega Mean longitude of the ascending node of the Moon coefficient 19- 27 F9.2 d Per Period of the nutation 29- 36 I8 uas as0i (a_s,0_)_i_ coefficient (1) 38- 42 I5 uas/hyr as1i (a_s,1_)_i_ coefficient (2) 44- 47 I4 uas/hyr2 as2i (a_s,2_)_i_ coefficient (2) 49- 52 I4 uas ac0i (a_c,0_)_i_ coefficient 54- 59 I6 uas/hyr ac1i (a_c,1_)_i_ coefficient 61- 62 I2 uas/hyr2 ac2i (a_c,2_)_i_ coefficient 64- 70 I7 uas bc0i (b_c,0_)_i_ coefficient (1) 72- 75 I4 uas/hyr bc1i (b_c,1_)_i_ coefficient (2) 77- 81 I5 uas/hyr2 bc2i (b_c,2_)_i_ coefficient (2) 83- 86 I4 uas bs0i (b_s,0_)_i_ coefficient 88- 93 I6 uas/hyr bs1i (b_s,1_)_i_ coefficient 95- 97 I3 uas/hyr2 bs2i (b_s,2_)_i_ coefficient -------------------------------------------------------------------------------- Note (1): The amplitudes (a_s,0_)_i_, (b_c,0_)_i_ are equal to the amplitudes A_i_.sin{epsilon}_0_ and B_i_ of the IERS 1996 series for nutation in longitude x sin{epsilon}_0_ and obliquity, except for 20 terms in each coordinate X and Y in which appears a contribution from crossed-nutation effect. Note (2): The amplitudes (a_s,j_)_i_, (b_c,j_)_i_, for j=1,2, are due to crossed terms between precession and nutation i, of the form t.sin or t.cos for j=1 and of the form t^2^.sin or t^2^.cos for j=2. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table1b.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 3 I3 --- i [1/112]+ Number i 5- 7 I3 --- lVe Mean longitude of Venus coefficient 9- 11 I3 --- lE Mean longitude of the Earth coefficient 13- 15 I3 --- lMa Mean longitude of Mars coefficient 17- 18 I2 --- lJ Mean longitude of Jupiter coefficient 20- 21 I2 --- lSa Mean longitude of Saturn coefficient 23- 24 I2 --- pa General precession in longitude coefficient 26- 27 I2 --- D Mean elongation from the Moon to the Sun coefficient 29- 30 I2 --- F L - Omega (L: Mean longitude of the Moon) coefficient 32- 33 I2 --- l Mean anomaly of the Moon coefficient 35- 36 I2 --- Omega Mean longitude of the ascending node of the Moon coefficient 38- 46 F9.2 d Per Period of the nutation 48- 50 I3 uas as0i (a_s,0_)_i_ coefficient 52- 53 I2 uas/hyr as1i (a_s,1_)_i_ coefficient 55 I1 uas/hyr2 as2i (a_s,2_)_i_ coefficient 57- 59 I3 uas ac0i (a_c,0_)_i_ coefficient 61- 62 I2 uas/hyr ac1i (a_c,1_)_i_ coefficient 64 I1 uas/hyr2 ac2i (a_c,2_)_i_ coefficient 66- 68 I3 uas bc0i (b_c,0_)_i_ coefficient 70- 71 I2 uas/hyr bc1i (b_c,1_)_i_ coefficient 73 I1 uas/hyr2 bc2i (b_c,2_)_i_ coefficient 75- 77 I3 uas bs0i (b_s,0_)_i_ coefficient 79- 80 I2 uas/hyr bs1i (b_s,1_)_i_ coefficient 82 I1 uas/hyr2 bs2i (b_s,2_)_i_ coefficient -------------------------------------------------------------------------------- Acknowledgements: Nicole Capitaine ================================================================================ (End) Patricia Bauer [CDS] 20-Mar-2000