[ntp:questions] Google and leap seconds

David Woolley david at ex.djwhome.demon.invalid
Thu Sep 22 07:26:00 UTC 2011


unruh wrote:
> On 2011-09-21, David Woolley <david at ex.djwhome.demon.invalid> wrote:
>> unruh wrote:
>>> On 2011-09-21, David Woolley <david at ex.djwhome.demon.invalid> wrote:
>>>> Richard B. Gilbert wrote:
>>>>
>>>>> It's unfortunate that the earth DOES NOT rotate exactly 360 degrees in 
>>>>> exactly 24.000000000000 hours. This bit of poor design causes all sorts 
>>>> It's nothing like it.  It out by approximately 1 degree a day!
>>> well, not if you define the rotation with respect to the "mean sun"
>>> rather than the stars. Then it is only out by a few PPB.
>>>
>> It makes a big difference for GPS, though.  I believe their orbital 
>> period is half a sidereal day, not 12 hours or even 43200 TAI seconds.
> 
> The orbit is far faster than that. You mean the period of the orbit (not
> in the orbit) as seen from earth. 
> 

I don't understand.

The orbit plane is fixed relative to the fixed stars, so, for the orbit 
to cover the same ground each time, it has to have a period that exactly 
divides the sidereal day.  The period is between successive maximum 
North points.




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