[ntp:questions] Google and leap seconds
unruh at wormhole.physics.ubc.ca
Thu Sep 22 16:09:59 UTC 2011
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.
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