On Tue 2014-11-04T21:52:05 +0000, Michael Deckers via LEAPSECS hath writ: > Then which unit would that be? When the IERS compute a difference > TAI - UT1, how do they do it? Do they convert the UT1 reading in > any way before they subtract? Or, if they don't, what is the unit > of the difference, SI seconds or "second of UT1"? The IERS > Conventions certainly do not mention any of this. How could they > if the units would really differ?
Guinot explained this using the term "graduation second" in section 2.2 of 1995 Metrologia 31 431 http://iopscience.iop.org/0026-1394/31/6/002 He points out that the way the IAU has written the definitions of the time scales uses a subtly ambiguous notation. He writes The numerical value of UT1(IERS)-TAI does not of course, express a duration. In this context, the "s" only conveys the information that the readings of the two time scales are expressed in graduation seconds. This is basically saying that UT1(IERS)-TAI is only a difference of two numbers. I think it's pretty much the same as supposing that a place with a comfortable temperature is cooling off and when the weather is freezing then the difference Delta T = T(deg Fahrenheit) - T(deg Celsius) = 32 degrees and when the temperature reaches -40 then Delta T = 0 degrees That difference is not a temperature, just like Delta T for eclipse timing predictions is not a duration. -- Steve Allen <[email protected]> WGS-84 (GPS) UCO/Lick Observatory--ISB Natural Sciences II, Room 165 Lat +36.99855 1156 High Street Voice: +1 831 459 3046 Lng -122.06015 Santa Cruz, CA 95064 http://www.ucolick.org/~sla/ Hgt +250 m _______________________________________________ LEAPSECS mailing list [email protected] https://pairlist6.pair.net/mailman/listinfo/leapsecs
