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Thread: how much does the sidereal year vary every year?

  1. #1
    Join Date
    Nov 2004

    how much does the sidereal year vary every year?

    Do interactions with the solar wind, gravitational effects from the planets, shifts in the gravity field of the Sun etc have any effects?
    "Occam" is the name of the alien race that will enslave us all eventually. And they've got razors for hands. I don't know if that's true but it seems like the simplest answer."

    Stephen Colbert.

  2. #2
    Join Date
    Feb 2003
    Depew, NY
    I would think so, but I also believe that a sidereal year is an average over an "age". I put the quotes around age because I mean it in the historical sense. You probably mean an exact measurement with modern tools.

    Hipparchus wrote a book (now lost) about the year and even with eye ball observations, he could see the limits of his tools (other observations and an armillae). However, he was able to deduce the sidereal year from the tropical year and vis--vis. What is interesting about Hipparchus' observations was, he was averaging the periodic terms to reduce the effects of perturbations. Being this would have been the 5th century BC, he was probably unaware of this effect.

    Ptolemy, who persevered the references to Hipparchus's work, believed the tropical year to be invariant which means he reached different conclusions.

  3. #3
    Join Date
    Jul 2005
    Massachusetts, USA
    I expect that the number one thing increasing the length of the Sidereal year is the tidal interaction with the Sun.
    Forming opinions as we speak

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