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Alpha
2011-12-19
2014-02-09
  • Alpha
    Alpha
    2011-12-19

    Hello

    I entered a date of -2000

    I noticed the pole star shifted considerably from the pole. Which should be
    the case.

    When I clicked on it, the ra and dec of the pole star on the upper left side
    of the screen where showing to be the existing values.

    Am I missing something

    The second question
    Will I be able to track lunar and solar eclipses to couple of thousands of
    years back, or the mathematical model was not intended to go back very far in
    time.

    Best regards

     
  • Alpha
    Alpha
    2011-12-19

    Many thanks for the reply

    My question actually why the information in the Stellarium is not updated (the
    ra and dec for the pole star ) when you click on it.

     
  • Bogdan Marinov
    Bogdan Marinov
    2011-12-19

    why the information in the Stellarium is not updated (the ra and dec for the
    pole star ) when you click on it.

    Which information? There are two pairs of RA/Dec values, one for the J2000.0
    epoch/coordinate system, one "of date" (corrected for precession).

    Will I be able to track lunar and solar eclipses to couple of thousands of
    years back, or the mathematical model was not intended to go back very far in
    time.

    No, you won't be able to. There are several issues preventing Stellarium from
    doing this, including the fact that it doesn't take into account "leap
    seconds".
    http://www.stellarium.org/wiki/index.php/Precision

     
  • Actually, I guess Stellarium updates continously the RA and DEC values. But,
    for "fixed" stars, you won´t able to see any significant difference in a long
    period of time because these are ecuatorial coordinates that, by definition,
    don´t change with Earth rotation and traslation. Only change because of the
    "Precession of the Equinoxes" (also "nutation" has a little effect), but this
    change is very slow along the years (a full cycle takes about 26000 years,
    more or less).

     
  • barrykgerdes
    barrykgerdes
    2011-12-24

    Stellatium uses the standard astronomical algorithms to calculate the position
    of all the astronomical bodies. Most of the distant objects will not change
    position noticably in millions of years and can be regarded as quite fixed.

    Some of the catalogues of stars particularly the hipparcos have a field that
    gives the anual motion and direction of the object.. Stellarium uses this
    information to reposition the objects as you advance or retard the calendar.
    It may not use the absolute precision but should be close enough over the
    range Stellarium is intended to work.

    Solar system objects also have a system of orbit parameters using data
    measured over time to calculate their position over the range that Stellarium
    is intended to work. This information of course can only be verified over the
    time used for the actual measurements. Outside this there could be many errors
    because no one knows if there have been or will be other astronomical events
    that have or will affect the orbits.

    Barry

     

  • Anonymous
    2013-10-05

    Stars change 1 degree every 70 years (precession)- does Stellarium take this into consideration if one wants to look at locations of constellations 2000 years ago?

     
  • Kird
    Kird
    2013-10-05

    "Stars change 1 degree every 70 years". When you make a statement like this you have to be more precise: the equatorial coordinates (and ecliptic longitudes) of stars change by about 1° every 72 years.
    Precession of the equinoxes causes a westward motion of the origin of the equatorial coordinate system compared to distant stars.
    Stellarium shows this. Try the following:
    Turn off ground display, atmosphere and cardinal points.
    Turn on the equatorial grid
    Switch to equatorial mount mode
    Select the star Polaris, and press SPACE to track it
    Press the J key about 10 times. Every 500 years press K to stop the motion and see the position of Polaris compared to the North Celestial Pole. With L you can go forward in time.

    You will also see that the coordinates of every star in a constellation change, but you will not see the form of the constellations change. You can also see the westward movement of the equinox when you go forward in time.

    http://en.wikipedia.org/wiki/Precession
    http://en.wikipedia.org/wiki/Equatorial_coordinate_system

     
    Last edit: Kird 2013-10-05

  • Anonymous
    2014-02-09

    In stellarium position of the moon is in aquarius but ecliptic topocentric of date is 340 degrees. What does this mean?

     


Anonymous


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