On Wed 2011-02-02T16:47:22 +0000, Stephen Colebourne hath writ: > - the SI-second is a standardised unit of measurement
which is a conventional construct that is valid in a particular reference frame. If I build a perfect cesium chronometer and you build a perfect cesium chronometer those will never agree because of our differences in relative velocity and depth in the varying gravitational potential wells. The only way to approach agreement is to apply corrections to the chronometer, thus changing it into a clock. The nature of the conventions under which the SI second is measured and integrated into a time scale have changed many times. > - the current definition of the SI-second was ratified in 1967 and the length of the SI second was chosen to match the length of the second of Ephemeris Time, which is actually a measure of angle. > - an SI-based-minute is formed from exactly 60 SI-seconds > - an SI-based-hour is formed from exactly 60 SI-based-minutes and thus > exactly 3600 SI-seconds > - an SI-based-day is formed from exactly 24 SI-based-hours and thus > exactly 86400 SI-seconds Given that no two observers are in the same reference frame, the notion of extending SI seconds into days requires delving into the years of discussions on the meaning of relativistic time scales. > Solar > - a solar-day is a measured period of time Not in the sense of metrology. A mean solar day is a conventional measure of rotation of the earth as differenced from a conventional reference point. The nature of the measure of the rotation angle and the conventional reference point have been changed many times. Yes, in the sense of human history and culture. -- Steve Allen <[email protected]> WGS-84 (GPS) UCO/Lick Observatory Natural Sciences II, Room 165 Lat +36.99855 University of California 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] http://six.pairlist.net/mailman/listinfo/leapsecs
