[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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