5 ms·

The rotation of Earth is actually not as stable a thing as one might expect. See for example http://en.wikipedia.org/wiki/Leap_second http://en.wikipedia.org/wi

• dfc 15y ago
  NIST recently published the new ntp.leap file and it looks like we will have one this July... 3550089600 35 # 1 Jul 2012 [1]
  • apaprocki 15y ago
    You also need to make sure your IANA tzdata is updated to account for this. I think this leap second was first added in tzdata2012a, but I'd have to check: ftp://ftp.iana.org/tz/data/leapseconds
    • acqq 15y ago
      If you use Unix time, you don't have to care: http://en.wikipedia.org/wiki/Unix_time http://en.wikipedia.org/wiki/Unix_time "Unix time, (...) is (...) defined as the number of seconds elapsed since midnight Coordinated Universal Time (UTC) of Thursday, January 1, 1970 (...) not counting leap seconds"
      • apaprocki 15y ago
        You might not be able to ignore leap seconds if you are interacting with an external system (software or hardware) / API that expects actual UTC. General rule applies to everything.. know your system, know what systems you are connected to, know what standards you need to adhere to. Microsoft apparently rejected the idea of using leap seconds because Windows just isn't accurate enough: The W32Time service uses the Network Time Protocol (NTP) in Microsoft Windows Server 2003, in Windows Server 2003 R2, in Windows Server 2008, and in Windows Server 2008 R2. ... The W32Time service cannot reliably maintain sync time to the range of 1 to 2 seconds. Such tolerances are outside the design specification of the W32Time service. http://support.microsoft.com/kb/939322 http://support.microsoft.com/kb/939322
        • acqq 15y ago
          Do you happen to know "an external system (software or hardware) / API that expects actual UTC"? Unix/Linux computers don't, Windows computers don't, GPS doesn't: http://en.wikipedia.org/wiki/Global_Positioning_System#Timekeeping_and_leap_seconds http://en.wikipedia.org/wiki/Global_Positioning_System#Timek...
          • apaprocki 15y ago
            GPS doesn't, but GLONASS does: GPS Time is designated as being coincident with UTC (USNO) at the start date of January 6, 1980 (00 hours). GPS Time does not count leap seconds, and therefore an offset exists between UTC (USNO) and GPS Time (at this date in April 2007: 14 seconds). Unlike GPS, the GLONASS time scale is not continuous and must be adjusted for periodic leap seconds. Leap seconds are applied to all UTC time references as specified by the International Earth Rotation and Reference System Service (IERS). Leap seconds are used to keep UTC close to mean solar time. Mean solar time, based on the spin of the Earth on its axis, is not uniform and its rate is gradually changing due to tidal friction and other factors such as motions of the Earth's fluid core. http://webone.novatel.ca/assets/Documents/Papers/GLONASSOverview.pdf http://webone.novatel.ca/assets/Documents/Papers/GLONASSOver... This is the best overview I've seen of all the pros/cons with regard to UTC and whether leap seconds should be abolished: http://www.agi.com/downloads/resources/user-resources/downloads/whitepapers/DebateOverUTCandLeapSeconds.pdf http://www.agi.com/downloads/resources/user-resources/downlo... Basically, much in the same way that we all despise DST (or date differences between Julian/Gregorian calendars), a certain part of me wants to know, if we humans last on this planet long enough, that our descendants thousands of years from now won't look back and curse at us for being idiots and deviating from celestial time.
          • dfc 15y ago
            A lot of RFCs, the first that comes to mind is the timezone seconds offset in DHCP replies and time fields in openpgp standard. Google probably knows a lot more: UTC site:rfc-editor.org