[LEAPSECS] tinkering with time ?

Warner Losh imp at bsdimp.com
Tue Feb 1 23:53:28 EST 2011

On 02/01/2011 17:00, Mark Calabretta wrote:

> On Tue 2011/02/01 11:37:59 -0000, Tony Finch wrote

> in a message to: Leap Second Discussion List<leapsecs at leapsecond.com>


>>> In the very distant future when the mean solar day is 86401 SI

>>> seconds long (or hopefully well before that), the pretence that

>>> the day is only 86400 SI seconds long, with its reductio ad

>>> absurdum result of a leap-second-per-day, should hopefully cause

>>> a re-examination of this convenient untruth.

>> On the other hand, dealing with that will only require a timezone

>> adjustment every ten years or so, which is perfectly tolerable.

> Let me put it this way. In the distant past there were only 86399 SI

> seconds in a day. Do we say today that there are 86399s with a leap

> second per day to bring it up to 86400s? Or do we simply say that

> there are 86400s per day?

there are 86400s per day because that's how a second was originally
defined. However, the second was redefined from a fraction of a day to
a number of oscillations of cesium atoms.

>> On the gripping hand, that will be tens of thousands of years in the

>> future, by which time the Gregorian calendar will no longer accurately

>> reflect the ratio between the length of the year and the length of the

>> day.

> Agreed. Which is to say that that the "quadratic blow out" in leap

> seconds is a specious argument which should be rejected.

The timeline for the Gregorian calendar to accumulate one 86400 SI s day
is on the order of 7.7k years. The quadratic collapse will have effects
much sooner than that. More on the order of 1200-1500 years, according
to the various projections of when more than 12s/year would be needed,
also the time frame and 3-4 hours of DUT1 accumulation. In 7.7k years,
about 48h of extra time would accumulate in the same time that the
Gregorian calendar would gain about a day since the current definition
of Gregorian calendar is 0.00013 days too long on the average. So the
combined effect would be about 3 days of error (3 days fast: 2 days from
SI ticking 1 day from accumulation of error between the average year in
the calendar and the average time it takes to go around the earth).

If I'm doing the math right, the average year will change from 365.24237
'days' to 365.24233 'days', but I may have inadvertently neglected the
Sidereal effects of the changing rotational period (from 86400.001s now
to 86400.033s in approx 7.7k years).


> Regards,

> Mark Calabretta



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