Coordinate Discrepancies between Vixen Starbook and Planetarium Software

[DeepSkyMan]

Hi there everyone, I have recently started experimenting with planetarium software in conjunction with my Vixen Starbook, ultimately the intention is to go with SkySafari, however in order to familiarise myself with connectivity requirements I thought I would have a go at using an ASCOM-based infrastructure, accordingly I downloaded the requisite ASCOM components and Cartes Du Ciel (CDC).  After getting everything connected up and working I then started issuing some gotos from CDC.  All seem to be working a treat, however on closer inspection I noticed that after issuing some gotos from CDC the objects were consistently off centre in the Starbook after completion of the slew.  Initially I thought the issue might be to do with the internal clocks being different by a minute or so between the PC and the Starbook, so I synced the times on the devices however the problem was still there.  I then discovered that the coordinates for objects which I had experimented with, were different between the Starbook and CDC. Take for example Capella:

Catalog                 RA                              DEC

Carte Du Ciel        05h17m46.45s          +46°00'25.4"

Starbook               05h17m48s               +46°0'

As a relative newcomer to the modern age of goto EQ mounts, I am puzzled that the coordinates should differ between the software implementation on the Starbook and planterium software.  Is this likely to be the case with other planetarium software solutions in conjunction with the Starbook?  In the greater scheme of things is the sort of difference we are talking about here going to materially affect observing sessions (be they Visual or Imaging)?  Note the above was purely an indoor familiarisation exercise, so I don't know if the inaccuracies noted would have impacted a real  observing session.  Can someone please shed some light on this conundrum?  

Kind Regards

Paul J.

 

Paul J.

[callump]

Sorry, i'm not really able to help specifically on CdC or Starbook, but perhaps one is running in year 2000 epoch, and one is showing current epoch (2014).

Stellarium shows both, but agrees with neither of your sets of numbers... 

/callump

[ronin]

I suspect that if you get 5 references then each one will be slightly different to the others.

Anyone creating a new coordinate reference will want their figures to be "unique" and if they turned out values identical to the one 5 years ago people would ask why they bothered and the "old" one would claim how good theirs was.

So I honestlly would expect differences, just very small ones.

[callump]

I'm not sure I understand your point - if I was creating some software I would want the numbers to agree with where the object actually is...

Anyway, I ran some calculations and it looks to me like the CdC numbers are pretty near right for Capella and Starbook is somewhat off. 

I did not calculate it out, but perhaps the Starbook is not taking proper motion into account - Capella being comparatively close has quite a high proper motion (so if you choose more distant objects the error may be less). Or possibly the Starbook has a bad PM catalogue.

I used the Simbad position for Capella (year 2000) added the proper motion and precessed the coordinates to arrive at 2014.7 coordinates, near enough...

/callump