1、12 Rec. ITU-R TF.457-2 RECOMMENDATION ITU-R TF.457-2 USE OF THE MODIFIED JULIAN DATE BY THE STANDARD-FREQUENCY AND TIME-SIGNAL SERVICES (Question IT-R 102R) ( 1970- 1974- 1997) The ITU Radiocommunication Assembly, considering that for dating purposes a decimal day count is desirable in connection wi
2、th the use of radio time signals and that a decimal day count with reference to universal time (UT), the Julian date (JD), has long been established that a decimal day count is necessary, by which the start of a day is defined at O000 hours and not at that a decimal day count is necessary, in partic
3、ular in association with the time scales coordinated universal that it is necessary to avoid a proliferation of different dating systems; that a simple change from the JD mentioned above to a modem decimal day count would be advantageous; that the existing and established JD, based on the start of t
4、he day being Greenwich Mean Noon, should be that a modified Julian date (MJD), which meets the requirements stated above, is already in use, a) radio time codes; b) for dating in astronomy, chronology and related sciences; c) 1200 hours as in the case of the JD; d) time (UTC) and intemational atomic
5、 time (TAI); e) f) g) continued without break; h) recommends 1 that for modem timekeeping and dating requirements, wherever necessary, a decimal day count should be used; the calendar day should be counted from O000 hours TAI, UTC or UT and be specified by a number with five significant figures; 2 that this “modified Julian date” (MJD) equals the JD less 2 400 000.5 and therefore has its origin, in the case of UT, at 0000 hours UT, 17 November 1858.
