[ntp:questions] Google and leap seconds

David Woolley david at ex.djwhome.demon.invalid
Thu Sep 22 22:36:15 UTC 2011


unruh wrote:
> On 2011-09-22, David Woolley <david at ex.djwhome.demon.invalid> wrote:
>> 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.
> 
> It is the sattelite you see, not the orbital plane. The sattelite goes
> around its orbit in a much shorter time period than one siderial day. 

Yes, as I said, it is HALF a sidereal day!
> 




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