It would be useful to have unchanging J2000 positions

[dbmcclain]

I cannot, as a professional Astronomer, envision the utility of reported J2000.0 positions which are continuously changing on screen.

J2000.0 positions are immutable, except for accumulated proper motion. The possibly useful articulated positions would be the apparent positions - those that exhibit at the moment, due to precession + nutation, and aberration. But you already have those. It could also be useful to see the accumulated proper motion reflected in your reported J2000.0 positions.

But seeing J2000.0 positions, articulated by anything more than proper motions, thwarts my ability to extract J2000.0 information which could be useful for other purposes.

As a case in point: The distant Quasar 3C273, near J2000.0 12h 29m 07.3s, +02° 03' 09", is so distant that it should have no observable proper motion. Hence the J2000.0 location should never change on screen. But when I speed up the passage of time, those coordinates are shown as continuously changing when they should not. It is fine to demonstrate the bouncing apparent position on screen - that's fun to see.

[gzotti]

What you see is presumably the effect of annual aberration. We cannot report catalog values and show aberration at the same time, as aberration is applied directly on the J2000 vectors. (User Guide, 4.3.) To remove the visible effect of aberration and the change in positional numbers caused by it, you must switch off aberration.

[dbmcclain]

Thanks for the information. Still a bit puzzling about Aberration being added to the J2000 vectors. I understand the process completely. But if you already have the J2000 vectors then why aren't you simply reporting those on screen, sans Aberration.

[gzotti]

Because you don't see the objects there at simulation time. Enable J2000 equatorial grid, kick in time-lapse, and see objects dance around in the grid. The numbers displayed are just those. To look up catalog values as professional astronomer, you certainly use SIMBAD.

[dbmcclain]

Okay, I am understanding you to say that it is a limitation due to the way the code has been written. I still want to add this issue to the Features Wish List.

[gzotti]

It goes against Stellarium's idea of visual simulation. We should not show objects with and tell you coordinates without aberration.

[github-actions]

This is not a bug! This is a feature...

[dbmcclain]

??? Aberration has nothing whatsoever to do with J2000.0 positions. These are coordinates expressed in the (mostly) immutable ICRS, referred to the mean Equinox of J2000.0. Your apparent positions reflect the aberration plus precession+nutation.

[gzotti]

We have technical and other reasons to do what we are doing. You may not like that. OK. To see J2000 coordinates without aberration in Stellarium, you can simply switch off aberration, so there is a solution. Call it a quirk. Stellarium is about pictures, not numbers, although we have found our ways to also provide good numbers now. The numbers that we need for display, not to please demands better fulfilled by catalog lookups.
As professional, you have certainly professional tools to provide subarcsecond-accurate positions including diurnal aberration, relativistic light bending and other effects.