[Info-vax] CRTL and RMS vs SSIO

[Phillip Helbig undress to reply]

In article <a5642b04-7036-464d-80ed-35b335fc69dfn at googlegroups.com>,
=?UTF-8?Q?Lawrence_D=E2=80=99Oliveiro?= <lawrencedo99 at gmail.com> writes:

> On Thursday, October 14, 2021 at 6:46:38 AM UTC+13, Simon Clubley wrote:
> > On 2021-10-13, Dave Froble <da... at tsoft-inc.com> wrote: 
> >> 
> >> Even simpler, since my computers run 24 x 365.25 
> >>
> > So you shut them down over a leap second ? :-)
> 
> Actually I think 365.25 is already about a quarter of an hour longer than an actual sidereal year, so leap seconds are going to be lost in the rounding error ...

365.25 would mean a leap year every 4 years.  The length is closer to 
365.2422.  365.2425 corresponds to missing 3 leap years every 400 years, 
which is what is done: a year divisble by 100 is not a leap year unless 
also visible by 400.  That was the case in 2000.  Had it not been, there 
might have been more Y2K problems.  :-|

So the current system is good for well over a human lifetime.

The leap seconds are added because the rotation rate of the Earth is 
slowing down, not to compensate for the inexact leap-year system, which 
is obviously off by much more than a second if it lets a day build up 
over 4 years.  The day was about 16 hours long earlier in the Earth's 
history.  Basically, the tides slow the Earth down.  As a result, the 
Moon recedes from the Earth.  Thus, the fact that it appears the same 
size as the Sun is not only a coincidence, but also one that holds now 
but not in general.

One can actually measure the change in the rotation rate of the Earth 
due to things like northern spring, when leaves appear on trees, 
increasing the moment of inertia and slowing down the Earth (and the 
opposite in northern autumn).