Stellarium

apparent plotting discrepancies

Asked by stev dieringer

is there a discrepancy in your plotting ?
There is a star/body that plots:
(equatorial grid): 12h 53m 11.8s -08deg 28’ 07.21”
(azmuthal grid): +85deg 20’ 18.65” -16deg25’44.73”)
But when targeted, has a readout (upper left of screen) of:
RA/DE (J2000) 12h 52m 36.3s -08deg 24’ 25.6”
which is considered the more reliable ? thanx, -stev

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Matthew Gates
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Best Matthew Gates (matthew-porpoisehead) said : 		#1

They are two different values. Because of the way the equatorial grid is defined, it drifts slowly over time, thus to have a really accurate coordinate one must specify the position and give a date for the grid. It is common for catalogs to normalize their positional data for a given date, e.g. the year 2000, even though the actual star positions may have been gathered over an extended period.

It is also common to use "Equatorial frame for the current date", which is what we simply refer to as RA and Dec.

Stellarium does the conversion on the fly, and provides both values for your convenience. Which one you will want to use depends on what you want to use the value for - if you want to compare to catalogs which are given in RA/Dec of the year 2000, use the 2000 values, else use the regular "of current date" values.

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stev dieringer (stev-stumpiesgrump) said : 		#2

Thanks Matthew Gates, that solved my question.

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stev dieringer (stev-stumpiesgrump) said : 		#3

Iyam a newbie & know enuf to be dangerous. as presented, this makes sense. I thankyou.