Proper motion of stars
Some time ago I posted a question regarding proper motion of stars in Stellarium. I then received an e-mail requesting further information. I sent this information by responding to this e-mail but got no response. Today I received an e-mail with a notification that the question (No. 293204) was closed due to missing response. Should I have sent the required information using this web site?
Anyway, I will repeat my question including the requested further information.
I am comparing declination values obtained by Tycho Brahe (1601) with values obtained using Stellarium and other planetarium programs as well as values calculated by myself correcting Hipparcos-2 values for proper motion and precession. For 15 stars investigated, the values obtained with Stellarium differ from 6" to 1' 54" compared with the other programs and my calculations.
As the object of my investigation is to determine the accuracy of Tycho Brahe's instruments (generally believed to be less than 1'), an error of more than 20" in declination obtained by the program providing the base line data is not acceptable.
Stellarium corrects for proper motion so this is not the cause for the discrepancy.
What may be the cause for the differences?
If necessary, I can provide actual values if necessary.
Thanks
The request for further information was: Which version of Stellarium are you using?
Do you take refraction into account?
My answer was: The version is 0.14.1beta.
I always correct Tycho's data for refraction. But that is not relevant to my question.
The difference I referred to was between declination values obtained using Stellarium and those calculated by me using declination values from Hipparcos-2 and then correcting these for proper motion and precession. Using other planetarium programs I obtained declination values very close to those I calculated.
In the table below, some of the declination values are listed. Other planetarium programs give values very close to those of Cartes du Ciel and my calculated values.
Stellarium 21 19 9 21,32 -18 -2 -6 -18,03 39 39 48 39,66
Cartes du Ciel 21 17 41 21,29 -18 -3 -55 -18,07 39 38 41 39,64
My calculation 21 17 37 21,29 -18 -3 -51 -18,06 39 38 44 39,65
I hope this clarifies my question.
Thank you
Ole Schou
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