Thus, the mean solar time is corrected for polar motion Uo=24110.54841+8640184581286610+ 09093104T20-62.106T UTI and the apparent sidereal time eo where To represents the timespan between the standard epoch J2000.0 (Julian centuries of 365.25 mean solar The mean sidereal time by neglecting the nutation term days) and the day of observation at oh UT. is a part of the navigation message broadcast by the UT1 UTC GPS satellites UTl=UTC+duTI When the absolute value of dUTI becomes larger than 0. 9, a leap second is inserted into the UTC system 3.3 Calendar Dynamic Time and Atomic Time System (GPS) The Julian Date (D) defines the number of mean solar days elapsed since the epoch 4713 B. C, January 1.5 IAT=GPS+19000 constant offset IAT= TDT-32 184 constant offset (3. 22) Modified . ulian I MuD) is obtained by subtracting 00.5 days from his convention saves digits and IAT=UTC +1.000 n variable offset as leap seconds are MJD commences at civil midnight instead of noon. ubstituted for example, the calculation of the parameter T for the dard epoch. Subtracting the respective Julian dates ing by 36525 (i.e, the number of days in a Julian entury)yields T=-0. 1998767967 Assignment 3 Summary 1. What are space-fixed and earth-fixed coordinate systems? Give the examples What have we learnt? 2. What are ecliptic plane, vernal equinox, node, Which parts are important? perigee, apogee, orbital plane? 3. What is orbital plane? 4. How many time system do you know? What is sidereal time and solar time 66 Thus, the mean solar time is corrected for polar motion UT1 and the apparent sidereal time Θ0. The mean sidereal time by neglecting the nutation term is a part of the navigation message broadcast by the GPS satellites. Time Series for υ0 υ0 = 24110s .54841 + 8640 184.s 812866 T0+ 0.s 093104 T2 0 -6.s 2 .10-6 T3 0 where T0 represents the timespan between the standard epoch J2000.0 (Julian centuries of 365.25 mean solar days). and the day of observation at oh UT. UT1 and UTC UT1 = UTC + dUT1 When the absolute value of dUTl becomes larger than 0.s 9, a leap second is inserted into the UTC system. Dynamic Time and Atomic Time System (GPS) IAT = GPS + 19.s 000 constant offset IAT = TDT -32.s 184 constant offset (3.22) IAT = UTC + l.s 000 n variable offset as leap seconds are substituted. 3.3 Calendar Definitions The Julian Date (JD) defines the number of mean solar days elapsed since the epoch 4713 B.C., January 1.d5. The Modified Julian Date (MJD) is obtained by subtracting 2400000.5 days from JD. This convention saves digits and MJD commences at civil midnight instead of noon. the Julian date for two standard epochs is given. This table enables, for example, the calculation of the parameter T for the GPS standard epoch. Subtracting the respective Julian dates and dividing by 36525 (i.e., the number of days in a Julian century) yields T = -0.1998767967. Summary What have we learnt? Which parts are important? Assignment 3 1. What are space-fixed and earth-fixed coordinate systems? Give the examples. 2. What are ecliptic plane,vernal equinox, node, perigee, apogee,orbital plane? 3. What is orbital plane? 4. How many time system do you know? 5. What is sidereal time and solar time? 6. What is GPS time?