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Chris L Peterson wrote:
>
> On Mon, 21 Apr 2008 10:48:09 -0700, David Weinshenker
> <daze39@xxxxxxxxxxxxx> wrote:
>
> >How would you measure the rotation: suppose you landed on this planet
> >from outer space, with your own time-measuring devices (that were marked
> >in some totally alien units, independent of Earthlings' "hours"), and
> >were wondering what the rotation period of the planet was. By what
> >observation would you take that measurement? (Observing the apparent
> >position of distant stars? Observing the position of sun? Using a
> >Foucault pendulum at the pole?)
>
> Which is very much the situation with us as the "aliens" when we measure
> the rotation period of every other body in the Solar System. We specify
> the period with respect to the stars (which is exactly what you would
> get with an inertial measurement, of course). In some cases, we
> _measure_ with respect to something else, such as an orbiting
> spacecraft. But then we convert to the inertial (sidereal) value.
Yeah, it seems that such distinctions are lost on "oriel36", who
seems to believe that there is something inherent or absolute about
the "24 hours = 360 degrees of rotation" relationship (independent
of how that rotation is measured), appears to be unaware that the
observation of stellar transits -is- a way of "isolating axial
rotation as an independent motion to be checked". and appears
not to have spent enough time observing the night sky to note
that particular stars do in fact rise "earlier" (relative to
the solar day of terrestrial timekeeping) each night.
-dave w
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