Hi-
I didn’t mean to direct anything at anyone specifically. This issue comes up often as an Epoch issue - and I brought the same thing up as an Epoch issue here some time ago - so I made the same mistake. But when it comes to plate solvers and mounts and all these things I think it helps to use the right terminology. Sources I like are the Meeus books, and the explanatory supplement to the astronomical almanac.
If a mount just uses star coordinates from the J2000 epoch then it really is using J2000 epoch if it doesn’t include proper motion - but it is using JNow equinox. The equations for precession with nutation are not that bad, so I expect mounts and planetarium programs use them. To get the moon right they would need to use topocentric observation coordinates - but whether they use them for all solar system objects I don’t know. And then the final thing is aberration and I assume TheSky includes that, on the arc-second scale.
The mount can use whatever it wants - and the application can use whatever it wants. But when coordinates are exchanged - the donor and receiver need to agree on what kind of coordinates are being provided.
Frank