F-ckin Leap Seconds, how do they work?

Tue Jul 3 23:06:20 UTC 2012

UTC and time is defined as part of the SI system and ITU etc, so we
just need to implement the time system correct. If you try to invent
your own way, there are surprises we don;t need to re-explore..

> On Tue, 03 Jul 2012 21:49:40, Peter Lothberg said:
> 
> > Leapseconds can be both positive and negative, but up to now, the
> > earth has only slowed down, so we have added seconds.
> 
> That's what many people believe, but it's not exactly right.  Leap seconds
> are added for the exact same reason leap days are - the earth's rotation
> isn't a clean multiple of the year.  We know we need to stick in an entire
> leap day every 4 years or so, then add the 400 hack to get it closer. At
> that point, it's *really* close, to the point where just shimming in a second
> every once in a while is enough to get it back in sync.
> 
> The earth's slowdown (or speedup) is measured by *how often* we
> need to add leap seconds.  If we needed to add one every 3 years, but
> the frequency rises to once every 2.5 years, *that* indicates slowing.
> In other words,  the slowdown or speedup is the first derivative of
> the rate that UT and TAI diverge - if the earth rotated at constant
> speed, the derivative would be zero, and we'd insert leap seconds on
> a nice predictable schedule.

I'm not an astronomer, but some of the errors we have in the second
intenmtion ended up in the earth position measurements, so the table
is not nicely spaced.. 

On one of my BSD boxes. /usr/src/share/zoneinfo/leapseconds, I see no
"-"

# @(#)leapseconds       7.17

# Allowance for leapseconds added to each timezone file.

# The International Earth Rotation Service periodically uses leap
  seconds
# to keep UTC to within 0.9 s of UT1
# (which measures the true angular orientation of the earth in space);
  see
# Terry J Quinn, The BIPM and the accurate measure of time,
# Proc IEEE 79, 7 (July 1991), 894-905.
# There were no leap seconds before 1972, because the official
  mechanism
# accounting for the discrepancy between atomic time and the earth's
  rotation
# did not exist until the early 1970s.

# The correction (+ or -) is made at the given time, so lines
# will typically look like:
#       Leap    YEAR    MON     DAY     23:59:60        +       R/S
# or
#       Leap    YEAR    MON     DAY     23:59:59        -       R/S

# If the leapsecond is Rolling (R) the given time is local time
# If the leapsecond is Stationary (S) the given time is UTC

# Leap  YEAR    MONTH   DAY     HH:MM:SS        CORR    R/S
Leap    1972    Jun     30      23:59:60        +       S
Leap    1972    Dec     31      23:59:60        +       S
Leap    1973    Dec     31      23:59:60        +       S
Leap    1974    Dec     31      23:59:60        +       S
Leap    1975    Dec     31      23:59:60        +       S
Leap    1976    Dec     31      23:59:60        +       S
Leap    1977    Dec     31      23:59:60        +       S
Leap    1978    Dec     31      23:59:60        +       S
Leap    1979    Dec     31      23:59:60        +       S
Leap    1981    Jun     30      23:59:60        +       S
Leap    1982    Jun     30      23:59:60        +       S
Leap    1983    Jun     30      23:59:60        +       S
Leap    1985    Jun     30      23:59:60        +       S
Leap    1987    Dec     31      23:59:60        +       S
Leap    1989    Dec     31      23:59:60        +       S
Leap    1990    Dec     31      23:59:60        +       S
Leap    1992    Jun     30      23:59:60        +       S
Leap    1993    Jun     30      23:59:60        +       S
Leap    1994    Jun     30      23:59:60        +       S
Leap    1995    Dec     31      23:59:60        +       S
Leap    1997    Jun     30      23:59:60        +       S
Leap    1998    Dec     31      23:59:60        +       S
Leap    2005    Dec     31      23:59:60        +       S
Leap    2008    Dec     31      23:59:60        +       S
Leap    2012    Jun     30      23:59:60        +       S

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