[ntp:questions] Google and leap seconds

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Thu Sep 22 18:41:26 UTC 2011


unruh wrote:
> On 2011-09-22, David Woolley<david at ex.djwhome.demon.invalid>  wrote:
>> 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.
>
David is correct, the GPS sats are in fact using orbits that have a 
period of almost exactly half sidereal day, or about 11 hours 58 minutes.

This is not a requirement though, afaik the upcoming Galileo sats will 
have significantly higher orbits/longer periods, but still a rational 
factor of the sidereal day, so that they will return to the same point 
after a number of days.

Terje

-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"




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