Coordinate mismatch between target and FOV center

[Alephinfi1]

I suspect a bug, but maybe I am wrong. Please consider the printscreen below. Although the telescope FOV and the target star are aligned, RA/DEC coordinates shown in yellow on the telescope FOV rectangle are different then the target white RA/DEC shown in the upper left corner. If I slew my mount to the yellow RA/DEC coordinates then the target star is in the center of my camera FOV; but if I slew to the target white RA/DEC, the target star is off (not even in my camera frame). That sounds very strange to me, counterintuitive at least.

Moreover, if I retrieve the target coordinates from the NINA framing tool, NINA gets the yellow coordinates, not the selected target's white coordinates. Is that the intended behaviour? Maybe it's NINA programmers that chose to pick the FOV coordinates, while Stellarium simply makes all of them available. Even though weired and the reason is not clear to me, the final behavior is correct in doing so: when you slew the mount, the target is in the center of the camera sensor.

And last question: is there an option to display the yellow FOV coordinates in Hour Dec format?

Many thanks for your help/inspection and best regards,
Davide Cattani

[10110111]

Well the labels say that one is the J2000 position, the other is of date.

[gzotti]

The infotext on top left is labeled "RA/dec (on date)"
The text at the box is labeled "RA/dec (J2000.0)"

How much clearer can we get? Please read about precession and its consequences for coordinates.

[gzotti]

About decimal hours: What's the application? Who uses that?

[github-actions]

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

[Alephinfi1]

Ok, I needed this confirmation and now I deduce all the rest:

• NINA's framing tool works in J2000 (not documented as far as I know)
• Mount's ASCOM driver Epoch is irrelevant: even though it is set to JNOW whilst NINA is J2000, pointing is precise once known that user must input coords in J2000 epoch
• Stellarium FOV RA/DEC is always J2000; I have not found an option to switch between J2000/JNOW, but known the rest this is not that important
• Stellarium can show Target RA/DEC both in JNOW and J2000 epoch, just found the option

• About decimal hours: What's the application? Who uses that?
  NINA's plugin "Sequencer Powerups", a very useful plugin that allows to set slew coordinates by variables and formulas (and much more) uses Hour Dec angles, see the printscreen below.

Sorry, I suspected that the epoch could be the reason but I didn't know the magnitude of the difference between JNOW and J2000; now I know it was not difficult to asses, but with all the other uncertanties above, that screwed my mind.

Thanks for your replies.
Davide

[gzotti]

IMHO using decimal hours in a GUI is a sign of developer fatigue. :-) I have never seen a list of coordinates in decimal hours in a printed publication. I suggest NINA devs could do something about it.
The coords near the box should be in the system configured for the respective telescope. There is some selector to override ASCOM setting, but any mismatch and consequences are up to you.

[Alephinfi1]

The coords near the box should be in the system configured for the respective telescope.

Actually the coords around the FOV yellow box are in J2000 whilst all the rest of the telescope settings are set to JNOW (I mean in Stellarium "Telescope Control" plugin and in the ASCOM driver); see the printscreen.

It looks like the FOV yellow box is J2000 independently from the other settings, nor it switches to JNOW when telescope is actually connected (I cannot connect the scope now to take a screenshot but I noticed it yesterday night); do you agree or did I maybe misunderstand your message?

[10110111]

The yellow box is provided by the Oculars plugin, no? It's completely separate from the Telescope Control plugin, I don't think they interact with each other in any way.

[gzotti]

Ah yes, right. Just that I don't use either on a regular basis. Is there no switch in the Oculars plugin then?

[10110111]

Is there no switch in the Oculars plugin then?

I could only find the switch between Alt/Az and RA/Dec, but not for the epoch of the latter.

[gzotti]

Interesting. maybe it reflects common practice then to frame with atlas coordinates. @alex-w ?

[alex-w]

Interesting. maybe it reflects common practice then to frame with atlas coordinates. @alex-w ?

Yes, all modern atlas has J2000.0 coordinates and center of CCD frame in the Oculars plugin has same epoch/frame for coordinates info.

[Alephinfi1]

Interesting. maybe it reflects common practice then to frame with atlas coordinates. @alex-w ?

Gzotti, still on this "Stellarium coordinates" topic, can you please help me understand why the star RA(Hour Angle)/DEC(deg) coordinates shown in the printscreen (in red) are completely different than those given by the converter, and why Stellarium's value change with time? Please see the printscreen: I input the green RA/DEC values in the converter but the result (in red) is completely different then Stellarium, and... doesn't change with time. If I slew to the converter's values I center the star, to the Stellarium's ones I don't. So confused..... :/

Many thanks!!

[gzotti]

RA=Right Ascension
HA=Hour Angle