On 2/15/12 10:22 PM, A C wrote: > Given the recent thread here about the upcoming leap second, I wanted to > know what additional service/value the leap second file provides that > isn't handled by ntpd receiving a message to add or remove a second. I > understand the generic ntpd documentation includes a flag to add a leap > second so it seems that the leap second file isn't necessary (and that's > also borne out in searches) but it must provide something otherwise it > wouldn't exist. The documents mention a "graceful" handling, but what > does that mean exactly?
A leap-second file is useful if you are processing archived time-stamped data and need to convert between TAI and UTC. When a future leap-second is announced and added to such a file, it is also useful when projecting future time-dependent events. In certain situations, the processing of time-stamped or time-dependent data requires uniform time intervals. That is, all minutes must be exactly 60 seconds in duration; all hours must be exactly 3600 seconds in duration; all days must be exactly 86,400 seconds in duration; etc. Such data should use TAI, which exhibits uniform intervals. To adjust such data to UTC, a leap-second file is useful. Why require a UTC adjustment from TAI? If the data represent a satellite orbiting the earth and the sub-satellite point on the earth's surface is needed, the TAI is converted to UTC, which is then converted through UT2 to UT1 and possibly to UT0 before obtaining the sidereal time. Sidereal time then gives the current angle of the earth's rotation for computing longitude. -- David E. Ross <http://www.rossde.com/> Concerned about someone (e.g., the government) snooping into your E-mail? Use PGP. See my <http://www.rossde.com/PGP/> _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
