BEST WALTHAM SIDEREAL?
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  1. #1
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    BEST WALTHAM SIDEREAL?

    Here is 10099659 21j model 92 made 1900. Googling for Waltham Sidereal gets a wide variety movements indicating these star timekeepers, of 3 minutes 58 seconds shorter than solar time of 24.00 hours, are not really rare. This 21j 24 hour dial seems to be the best if not rarest. Certainly the best looking 92 movement I have. The case is a fine quality screw threads front and glass back

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    Last edited by artb; July 12th, 2013 at 08:03.
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    Member AbslomRob's Avatar
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    Re: BEST WALTHAM SIDEREAL?

    I'll admit that I've never really understand the distiction between sidereal time and "normal" time, but isn't this just a normal watch with a 24 hr. dial? Is it "sidereal" because the hour hand only makes one revolution per day?
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  3. #3
    Member HOROLOGIST007's Avatar
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    Re: BEST WALTHAM SIDEREAL?

    Agree that its not showing the difference between a normal 24 hour 'clock' day time and true Sun time. There are timepieces that truly display the 'equation of time'
    That said its a LOVELY movement

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    NEVER ARGUE WITH AN IDIOT. FIRST THEY WILL DRAG YOU DOWN TO THEIR LEVEL. THEN, THEY WILL BEAT YOU WITH EXPERIENCE.

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    Vintage & NAWCC Forum moderator Ben_hutcherson's Avatar
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    Re: BEST WALTHAM SIDEREAL?

    These watches are regulated to sidereal time, i.e. they run ~4min slow per day relative to a watch keeping "normal" time.
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    Member Eeeb's Avatar
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    Re: BEST WALTHAM SIDEREAL?

    Quote Originally Posted by Ben_hutcherson View Post
    These watches are regulated to sidereal time, i.e. they run ~4min slow per day relative to a watch keeping "normal" time.
    As I understand it, a normal watch will say it is 'noon' and the sun will be directly overhead (assuming you are in the exact middle of a time zone) but the stars could be anywhere at that time.

    A sidereal watch will say it is 'noon' and the same set of stars will be overhead - but the sun could be anywhere.

    Is this correct? Close even?

    I assume these are very useful for navigation.
    Last edited by Eeeb; July 12th, 2013 at 15:18.
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    Member HOROLOGIST007's Avatar
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    Re: BEST WALTHAM SIDEREAL?

    Quote Originally Posted by Ben_hutcherson View Post
    These watches are regulated to sidereal time, i.e. they run ~4min slow per day relative to a watch keeping "normal" time.
    Ben
    That is most interesting
    Thanks for letting us know.
    Regards
    adam
    NEVER ARGUE WITH AN IDIOT. FIRST THEY WILL DRAG YOU DOWN TO THEIR LEVEL. THEN, THEY WILL BEAT YOU WITH EXPERIENCE.

    "Failure is not an option" - Gene Kranz
    "Owning a vintage watch is great, understanding where it sits in Horology is magnificent"
    and
    "By Teaching Others, We Teach Ourselves"
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  8. #7
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    Re: BEST WALTHAM SIDEREAL?

    This sidereal has proper gear ratios to be accurately adjusted for the exact near 3 minutes 58 seconds slower running. There are some adjusted for slower speed 12 hour dial so called sidereals, but this one is a serious optimized for the purpose one.

  9. #8
    Member HOROLOGIST007's Avatar
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    Re: BEST WALTHAM SIDEREAL?

    Quote Originally Posted by artb View Post
    This sidereal has proper gear ratios to be accurately adjusted for the exact near 3 minutes 58 seconds slower running. There are some adjusted for slower speed 12 hour dial so called sidereals, but this one is a serious optimized for the purpose one.
    I was going to comment its not exactly 4 minutes, but decided not to bother.

    Its most interesting. I also thought the differece varied (changed) over the year i.e variation be tween summer and winter to a maxm 3mins 58 secs?

    Thanks for explaining
    Regards
    NEVER ARGUE WITH AN IDIOT. FIRST THEY WILL DRAG YOU DOWN TO THEIR LEVEL. THEN, THEY WILL BEAT YOU WITH EXPERIENCE.

    "Failure is not an option" - Gene Kranz
    "Owning a vintage watch is great, understanding where it sits in Horology is magnificent"
    and
    "By Teaching Others, We Teach Ourselves"
    Adam

  10. #9
    Zenith Forum Co-moderator
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    Re: BEST WALTHAM SIDEREAL?

    Unlike solar time, which also depends on the speed at which the earth goes round the sun (which isn't constant, leading to the "equation of time"), sidereal or stellar time depends solely on the rotation of the earth around its own axis. There is therefore no need for an equation of time on a sidereal watch - the 3 minutes 58 seconds are a constant.

    Hartmut Richter

  11. #10
    Member tinknocker's Avatar
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    Re: BEST WALTHAM SIDEREAL?

    very informative, I had not heard of this before. Thanks

    The movement is stunning as is the rest of the watch.
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