RA/DEC J2000 of stars

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VReijs
2013-02-06
2015-04-22
  • VReijs

    VReijs - 2013-02-06

    Hello, I have a query about the RA/DEC coordinates of stars in Stellarium (0.12.0).

    For Arcturus I get a RA/DEC (J2000) of 14h22m2.1s/+22deg30'29.7"
    What star catalogue is this: I think it is NOMAD, correct?

    If I check Tycho2 (like used in SkyMap Pro 9), I get a RA/DEC (J2000) of 14h15m39.673s/+19deg10'56.688"

    SimBAD database gives: 14 15 39.67207 +19 10 56.6730
    (http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=arcturus&submit=SIMBAD+search )

    Hipparcus give (J2000):
    _RAJ2000 14 15 39.672 and _DEJ2000 +19 10 56.67
    (http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIP%2069673 )

    Why this difference in Stellarium? It can't be proper motion (as we use the reference data J2000 in all cases).
    I see similar difference for other stars...

    Le me know if I understand the coordinates properly. Thanks.

    All the best,

    Victor

     
  • barrykgerdes

    barrykgerdes - 2013-02-06

    My Stellarium shows Arcturus as
    14h15m35.5s/+19d10'45.3" for j2000

    Barry

     
    • VReijs

      VReijs - 2013-02-06

      Hello Barry,

      What Stellarium version do you have? Your RA/DEC values look much better.
      I am looking at the data that is show if I left click the star.
      Thanks for your help.

      On 6 February 2013 21:05, barrykgerdes barrykgerdes@users.sf.net wrote:

      My Stellarium shows Arcturus as
      14h15m35.5s/+19d10'45.3" for j2000

       
  • Alexander Wolf

    Alexander Wolf - 2013-02-07

    Info from my Stellarium for current date:

    Arcturus (α Boo) - HIP 69673 A
    Type: double star
    Magnitude: 0.15 (extincted to: 0.44. B-V: 0.82)
    Absolute Magnitude: -0.11
    RA/DE (J2000): 14h15m39.5s/+19°10'45.3"
    RA/DE (of date): 14h16m16s/+19°07'08"
    Galactic longitude/latitude (J2000): +15°02'27.7"/+69°06'38.5"
    Hour angle/DE: 3h08m53s/+19°07'08" (geometric)
    Hour angle/DE: 3h08m51s/+19°07'45" (apparent)
    Az/Alt: +244°59'15"/+40°22'54" (geometric)
    Az/Alt: +244°59'15"/+40°23'38" (apparent)
    Spectral Type: K2IIIp
    Distance: 36.71 Light Years
    Parallax: 0.08885"

    Your coordinates - RA/DEC (J2000) of 14h22m2.1s/+22deg30'29.7" - was correct for Feb of -3335 :)

     
    • VReijs

      VReijs - 2013-02-07

      Hello Alexander,

      RA/DE (J2000): 14h15m39.5s/+19°10'45.3"

      Your coordinates - RA/DEC (J2000) of 14h22m2.1s/+22deg30'29.7" - was
      correct for Feb of -3335 :)

      For me 9and I think in general) the RA/DEC(J2000.0) is a constance: as I
      think in is the definition of where the star is on date J2000.0 So these
      values don't change regardless of the date/location one is on/in.
      See for instance Skymap and other programs where the reference RA/DEC is
      constant.

      So what is you definition of RA/DE(J2000)?

      All the best,

      Victor

       
      • VReijs

        VReijs - 2013-02-09

        Hello Alexander,

        Is there a way to find what proper motion stars have (I think it is not in
        the object information, correct)?
        As for Sirius I see in Stellarium (using date/time 2000/1/1 12:00:00) a
        different RAJ2000 and DEJ2000 in the Hipparcos catalogue (
        http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIP%2032349 ), I don't just
        want to use the proper motion mentioned in Hipparcos.

        Thanks for your help.

        All the best,

        Victor

        On 7 February 2013 18:31, Victor Reijs web.victor.reijs@gmail.com wrote:

        Hello Alexander,

        RA/DE (J2000): 14h15m39.5s/+19°10'45.3"
        Your coordinates - RA/DEC (J2000) of 14h22m2.1s/+22deg30'29.7" - was
        correct for Feb of -3335 :)

        For me 9and I think in general) the RA/DEC(J2000.0) is a constance: as I
        think in is the definition of where the star is on date J2000.0 So these
        values don't change regardless of the date/location one is on/in.
        See for instance Skymap and other programs where the reference RA/DEC is
        constant.

        So what is you definition of RA/DE(J2000)?

        All the best,

        Victor

         
        • Alexander Wolf

          Alexander Wolf - 2013-02-10

          Is there a way to find what proper motion stars have (I think it is not in the object information, correct)?

          Yes, we don't display this information.

          You can found information about proper motion of stars in Hipparcos, Tycho 2, UCAC, etc. catalogs: http://cdsarc.u-strasbg.fr/viz-bin/Cat?cat=proper+motion&find=+

           
          • VReijs

            VReijs - 2013-02-10

            Hello Alexander,

            I know the catalogues, but I need to know what Stellarium is using for say
            Sirius. There are so many values floating around in these catelogues for
            the same object and I want to understand what Stellarium does and for that
            I need the values actually used in Stellarium. The cat. files are binaries
            so I have no real method of looking at them.

            As you use Hipparcos serial number for Sirius (HIP32349) I thought
            Stellarium would use Hipparcos catalogue, but that catalogue has different
            values for RA and DE J2000 than Stellarium displays, so I don't just want
            to copy the proper motion values.

            Hope you can help.

            All the best,

            Victor

            On 10 February 2013 10:45, Alexander Wolf alexvwolf@users.sf.net wrote:

            Is there a way to find what proper motion stars have (I think it is not in
            the object information, correct)?

            Yes, we don't display this information.
            You can found information about proper motion of stars in Hipparcos, Tycho
            2, UCAC, etc. catalogs:
            http://cdsarc.u-strasbg.fr/viz-bin/Cat?cat=proper+motion&find=+

            RA/DEC J2000 of starshttps://sourceforge.net/p/stellarium/discussion/278769/thread/f7ac2a5e/?limit=25#fd64/5a31/d735/78a5

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            • Alexander Wolf

              Alexander Wolf - 2013-02-10

              For Sirius Stellarium use Hipparcos (first edition).

              Information about our catalogs: http://www.stellarium.org/wiki/index.php/Star_Catalogue#Star_Catalogue_File_Format

              Note: original catalogs can have coordinates for different epochs

               
              • VReijs

                VReijs - 2013-02-10

                Thanks Alexander,

                So If I use Hipparcos I get the attached RA/DEC values (the web page:
                http://www.rssd.esa.int/index.php?project=HIPPARCOS&page=multisearch2 )
                super imposed on Stellarium at 2000/1/1 12:00:00 UT and SkyMap (same
                date/time).
                As you see the web page has almost the same value as Stellarium/SkyMap
                (which uses Tycho 2), BUT the web page (aka Hipparcos), is not at J2000.0
                but at 1991.25! ( see here:
                http://www.rssd.esa.int/SA/HIPPARCOS/docs/ReadMe.hsearch )

                I attached two screen grabs (one where SkyMap and Stellarium are at 2000101
                12:00 and one at 19910101 18:00).

                So it looks Stellarium uses Hipparcos data as if it is from J2000.0 while
                it should compensate it from J1991.25.
                Or do I misinterpratate it?

                All the best,

                Victor

                On 10 February 2013 11:31, Alexander Wolf alexvwolf@users.sf.net wrote:

                For Sirius Stellarium use Hipparcos (first edition).

                Information about our catalogs:
                http://www.stellarium.org/wiki/index.php/Star_Catalogue#Star_Catalogue_File_Format
                Note: original catalogs can have coordinates for different epochs

                RA/DEC J2000 of starshttps://sourceforge.net/p/stellarium/discussion/278769/thread/f7ac2a5e/?limit=25#fd64/5a31/d735/78a5/a316/27b4

                Sent from sourceforge.net because you indicated interest in
                https://sourceforge.net/p/stellarium/discussion/278769/

                To unsubscribe from further messages, please visit
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                • Alexander Wolf

                  Alexander Wolf - 2013-02-10

                  Stellarium used Hipparcos catalog, which has been recalculated from J1991.25 to J2000.0.

                  P.S. SourceForge drops attachments.

                   
                  Last edit: Alexander Wolf 2013-02-10
                  • VReijs

                    VReijs - 2013-02-10

                    Hello Alexander,

                    Indeed that is what I also thought and try to tell that something is not
                    fully correct:
                    According to the web site you give (
                    http://www.rssd.esa.int/index.php?project=HIPPARCOS&page=multisearch2 )
                    Sirius is in Hipparcos catalogue (being J1991.25) at:
                    H| 32349| |06 45 09.25|-16 42 47.3

                    If I look at Stellarium on J1991.25 I get:
                    RA/DE (J2000): 6h45m9.6s/-16°42'35.8"

                    And on J2000.0 I get in Stellarium:
                    RA/DE (J2000): 6h45m9.3s/-16°42'47.3"

                    So Stellarium J2000.0 is very close to the values I see in Hipparcos
                    catalogue (which is at J1991.25). So something is wrong. Or I dont;
                    understadn it or Stellarium use the wrong date fro Hipparcos catalogue.

                    All the best,

                    Victor

                    On 10 February 2013 15:51, Alexander Wolf alexvwolf@users.sf.net wrote:

                    Stellarium used Hipparcos catalog, which has been recalculated from
                    J1991.25 to J2000.0.

                    RA/DEC J2000 of starshttps://sourceforge.net/p/stellarium/discussion/278769/thread/f7ac2a5e/?limit=25#fd64/5a31/d735/78a5/a316/27b4/528a/c59a

                    Sent from sourceforge.net because you indicated interest in
                    https://sourceforge.net/p/stellarium/discussion/278769/

                    To unsubscribe from further messages, please visit
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                    • barrykgerdes

                      barrykgerdes - 2013-02-10

                      Hi Victor
                      What is the point of this

                      The error based on the catalogue values we use is only on the precision of the conversion of a decimal value into hrs,mins and secs. If the data base is 4 decimal places and the value is converted twice in the program from the j1999.5 value the error could certainly be as you see it.

                      I regularly get small discrepancies depending on date and time because of this. If you need greater accuracy you will need to use the Hipparcos catalogue and write a small program to change the epoch to a higher precision. I have a number of programs written in Qbasic that will do this.

                      Barry

                       
                      Last edit: barrykgerdes 2013-02-10
                      • VReijs

                        VReijs - 2013-02-11

                        Hello Barry,

                        Don't understand, your point. If a normal computer language is not able to
                        handle 4 decimals behind the dot, then I am wondering.

                        And by the way my point is different! Did you see that the J2000 in
                        Stellarium is precisely the value that is defined in Hipparcos at J1991.25,
                        so I think something else is happening...

                        All the best,

                        Victor

                        P.S. Also J2000.0 means a reference date and thus the RA/DE has to be
                        constant. So the changing RA/DE(J2000) is not correct, IMHO. It now looks
                        to include the proper motion (but not sure), which I would not label as
                        'RA/DE(J2000)'! I don't know if there is a name for it...

                        On 10 February 2013 20:37, barrykgerdes barrykgerdes@users.sf.net wrote:

                        Hi Victor
                        What is the point of this

                        The error based on the catalogue values we use is only on the precision of
                        the conversion of a decimal value into hrs,mins and secs. If the data base
                        is 4 decimal places and the value is converted twice in the program from
                        the j1999.5 value the error could certainly be as you see it.
                        Barry

                        RA/DEC J2000 of starshttps://sourceforge.net/p/stellarium/discussion/278769/thread/f7ac2a5e/?limit=25#fd64/5a31/d735/78a5/a316/27b4/528a/c59a/ef77/5311

                        Sent from sourceforge.net because you indicated interest in
                        https://sourceforge.net/p/stellarium/discussion/278769/

                        To unsubscribe from further messages, please visit
                        https://sourceforge.net/auth/prefs/

                         
  • barrykgerdes

    barrykgerdes - 2013-02-07

    All versions fro 0.10.3 to 0.12.1
    The only way those coords could show this is the date was milleniums out

    Barry

     
  • Anonymous - 2015-04-21

    Has this query I had, been solved? I did not do a check, but perhaps someone knows if this problem is rectified. Thanks for any feedback.

     
  • Anonymous - 2015-04-22

    I now see it has been changed. Sorry I should have checked earlier. Great!
    I see that Stellarium now reports J1991.0 as its basis and the RA/Dec of date looks also correct (comparing to Hipparcos database and SkyMap). Thanks for improving this (perhaps already some time ago). So now I can change my advice to other archaeoastronomy people.

    All the best,

    Victor

     


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