More on TiPS orientation

Robert H. McNaught, Anglo-Australian Observatory (
Sun, 14 Jul 1996 14:58:16 +1000 (EST)

Sue Worden's comments on the TiPS orientation are caused by a confusion
between the actual (3-D) orientation and the apparant orientation.  It is
the apparent orientation that is you see in binoculars, so it is necessary to
ignore questions of what is farther or closer.  It is probably non intuitive
that a vertical tether will remain vertical throughout the whole observed pass
but that is the case!  Regarding passage thru the exact zenith, this is a
special case but does not contradict the argument.  An infinitesimally
small time before and after the tether drops to zero apparent length, it has
a vertically orientated infinitesimally small size.

These arguments are all based on an ABSOLUTE (3-D) vertical orientation.
(Thanks Jim for the physics of why this is so).  However if the deployment is
not made vertically, I assume the tether would oscillate like a pendulum.
Perhaps someone could calculate the oscillation period?  If the apparent
orientation is EVER non-vertical, this means that it is not vertical in 3-D.

Cheers, Rob McNaught