Tracking rates & ephemeride units of time

American Association of Variable Star Observers (AAVSO)
Tue, 11/05/2019 - 18:46

I have run into a situation in which telescope tracking rates except for the solar tracking rate are specified in terms of arcseconds/per sidereal second rather than arcseconds/per normal (TAI) second. The reason given by the telescope manufacturer is that ephemerides are commonly specified in arcseconds/sidereal second. The result of this is that the telescope solar tracking rate is 15 arcsec per second (clock second) and sidereal tracking is also shown as 15 arcsec/sec (but the units are sidereal seconds) and custom tracking rates also must be entered in arcsec per sidereal second.  

I had never run into tracking rates or ephemerides expressed in motion per unit of sidereal time and I was wondering if this is indeed a common practice at professional observatories and for ephemerides of planets asteroids, comets or other astronomical objects.  


Brad Walter, WBY