When the Great Pyramid was built, one long sloping tunnel was aimed at a particular star, which could be seen by a person at the bottom of that tunnel on just one night of the year. Today that star is no longer visible from the bottom of that tunnel, because stars have shifted positions in the night sky over the millennia. The term for this is something like presension of the equinox, but that is not quite it. What is the proper term?


1 Answer 1


It is called precession. The rate of change is about 1 degree every 72 years. Since the pyramids were built about 4500 years ago, the Earth's pole has precessed about 62 degrees since then. The entire cycle takes about 26,000 years.

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    $\begingroup$ Precession is part of it, but stars also have proper motion, meaning they are moving in space relative to us. Barnard's star, for example, has a proper motion of 10.39 arcseconds per year. Depending on the star in question, proper motion may be significant or negligible over 10,000 years. $\endgroup$
    – Dan Hanson
    Aug 13, 2022 at 2:12
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    $\begingroup$ @DanHanson have you compared the proper motion of any naked eye star with precession? $\endgroup$
    – ProfRob
    Aug 13, 2022 at 7:15
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    $\begingroup$ @DanHanson Barnard's Star is only 6 ly away, one of the closest stars, so it has an abnormally high proper motion. The vast majority of visible stars are at least an order of magnitude more distant, with much lower proper motions. $\endgroup$
    – Barmar
    Aug 13, 2022 at 15:15
  • $\begingroup$ The OP was clearly asking about precession. $\endgroup$ Aug 13, 2022 at 19:50

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