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Thread: Vega as Pole Star

  1. #1
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    Vega as Pole Star

    The astronomy software I use (Skygazer 4.5) shows Vega within 2.5 degrees of the North Celestial Pole for two centuries from 12300 BC. A friend said their software never showed Vega closer than five degrees from the pole. What factors might cause this discrepancy? What might be the most reliable figure?

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    Quote Originally Posted by Robert Tulip View Post
    The astronomy software I use (Skygazer 4.5) shows Vega within 2.5 degrees of the North Celestial Pole for two centuries from 12300 BC. A friend said their software never showed Vega closer than five degrees from the pole. What factors might cause this discrepancy? What might be the most reliable figure?
    The factor that would cause that is probably a bug in your friend's software. The axis of the Earth's rotation extends to a point in the sky, about which everything else in the sky appears to rotate. This point moves in a circle around the northern celestial sphere over a period of about 26,000 years. Right now it happens to point very close to Polaris which is quite the coincidence, Polaris being one of the brighter stars in the sky. If you were to draw this 26k year circle on the celestial sphere, you would see that one part of the circle is very near Vega, so your software is probably more accurate than your friend's.



    From Wikipedia: "Vega was the northern pole star around 12,000 BC and will be so again around the year 13,727, when its declination will be +86 14′."
    So, perhaps the correct answer is halfway between your figure of 2.5 degrees and his of 5. In software, such problems are often caused by rounding error. You can try upgrading to software that uses 64-bit doubles instead of 32-bit floats, that kind of thing. Hope this helps!
    Last edited by CaptainToonces; 2021-Aug-21 at 09:15 PM.

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    Your image is showing just precession on stationary fixed stars. What are you assuming as proper motion of Vega?

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    Quote Originally Posted by chornedsnorkack View Post
    Your image is showing just precession on stationary fixed stars. What are you assuming as proper motion of Vega?
    I looked up proper motion information and found the following.

    SkyGazer is a 10,000 year component of the Voyager software program, which accurately models the precession of the Earth's axis and the motions of the stars and planets back to the dawn of humanity. The website has a star map showing when Aldebaran and Capella were together at the north pole half a million years ago!

    Vega has angular movement of a degree every 11,000 years (link).

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