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Perpetual Calendar; Year 4000-and-beyond

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  • Frank Ferrell
    Greetings ...

    It was 2006 (previous edit) and now it's 2017 (latest edit), and we are using Year Calendar 1 - my top favorite Year Calendar, followed by 14, 6, 12, 4, 10, 3 and 9.

    Thanx-A-Lot and Enjoy, Frank
    Last edited by Frank Ferrell; 18 Feb 2017, 04:56 PM.

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  • Egbert Zijlema
    Feel free to download a fistful of calendar code here:

    Egbert Zijlema, journalist and programmer (bas underscore guru at planet dot nl)

    Opinions expressed here are not necessarily true

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  • Donald Darden
    The 4-year, 100-year, and 400-year rules are approximations.
    Actually, they are quite good as far as they go. In continuing
    to look further, we are faced with the fact that the revolution
    of the earth slows down due to pull from the moon, making our
    days longer, and the moon moves further from the earth over time,
    which may increase the degree of wobble in the earth's rotation,
    and as we've just learned, major disturbances on the earth can
    also effect the earth's spin on its axis or the tilt of that
    axis. On top of that, the movement of the earth around the sun is
    not precise from one orbit to the next. There are suspicions that
    some orbits may extend the year and move the earth further from
    the sun, adding to the tendency of cyclic ice ages.

    The problem is that adding or deleting a day in the calendar is a
    coarse adjustment. Depending on all these factors, the need to
    make a change is likely a belated adjustment, or one where you
    cross the midpoint and create error in the opposite direction by
    overkill. My previous experience showed that every 2000 years
    was one of the possible adjustment points as you try to tweak
    the calendar +/- one day at a time, but we are pass that point
    now. Another adjustment point is every 23,000 years, but I
    imagine this will be quite a different world by then, so I think
    I will hold off on devising a rule for that situation.

    Who knows? We may revise our calendar so that each month has 28
    days, and there are thirteen months in all. Then we have one to
    three days at the end of the year to party and tinker with before
    we start the year over. Instead of twelve monthly calendars, you
    only need one, since each calendar day for the year will fall on
    the same day of the week. We can adjust our new calendar so that
    either the year starts with the shortest day of the year, or
    look to moving things around so that month 13 covers the present
    month of October - that way people who believe that thirteen is
    unlucky can practice other superstitions during that period.

    Old Navy Chief, Systems Engineer, Systems Analyst, now semi-retired

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  • Frank Ferrell
    Greetings --

    UPDATE: 1-08-2005

    As Calendars and Time Keeping are important programming elements -- be it in PowerBasic DOS or any other language -- I thought I would revive this topic.

    Thanx-A-Lot, Happy New Year and Enjoy, Frank

    Last edited by Frank Ferrell; 20 Mar 2016, 08:55 PM. Reason: Removing dead links

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  • Kurt Schultz
    I wrote an article about this:

    The 'truth'-ness of the leapyear situation oscillates FTFT.

    "Default Rule: A year will not be a Leap Year.
    1st Exception: If the year value leaves a remainder of zero
    when it’s divided by four, it will be a Leap Year.
    2nd Exception: If the year value leaves a remainder of zero
    when it’s divided by 100, it will not be a Leap Year.
    3rd Exception: If the year value leaves a remainder of zero
    when it’s divided by 400, it will be a Leap Year."

    The application of Modular Arithmetic ought to be obvious.
    It boils down to a 4-step ladder of IF statements.

    The next exception might appear to be 10,000, but I'm not sure
    that it is wise to extrapolate out that far. The situation may
    not resolve with the expected regularity, and the Earth will
    have slowed by then.

    In all of my studies, there was no indication at all of any
    exception for an interval greater than the 400 year interval.


    In Re: The Gregorian Calendar, be careful about the 'beginning'
    of it. To accurately emulate the beginning, you have to
    consider the geographic location in question as well as the
    temporal location in question, because it was not uniformly
    adopted everywhere at the same time. Even different regions of
    some countries adopted the new calendar at different times,
    usually for religious reasons.

    This particular programming problem turned out to be so complex
    that I gave up in horror and decided to pick something simpler.

    Kurt Schultz
    [email protected]

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  • Frank Ferrell
    A previous "BUMP" message, which the Forum Moderator may delete.

    [This message has been edited by Frank Ferrell (edited January 08, 2005).]

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  • Colin J Donoghue
    Guest replied
    You sure are the epitome of an optimist, but assuming that 1) humanity, 2) computers, and 3) your program still exist in another 2,000 years, take a look at this URL:
    Good luck,


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  • Frank Ferrell
    Greetings ---

    Matthew -- Thanx for that link - it's a keeper!

    They've changed the link since you first posted it. Here's the new one--
    Isn't there a 4000-yr rule?

    Tom -- Since the time these postings first appeared (Fall 2001), I have chosen to program PERCAL without using the 3300 year deal you mention. Nor does PERCAL have adjustments for year 4000, 8000, etc.

    I thank you for your info just the same!

    Thanx-A-Lot, Happy New Year and Enjoy, Frank

    Last edited by Frank Ferrell; 20 Mar 2016, 08:53 PM. Reason: Replacing Dead Link

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  • Matthew Berg
    Isn't there a 4000-year rule?

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  • Tom Hanlin
    Ahh, the dread "Y4K bug"... could be that the rumors aren't exaggerated. According to the U.S. Naval Observatory, Astronomical Applications Department, "It will take about 3300 years before the Gregorian calendar is as much as one day out of step with the seasons." Question is, of course... why care?

    Supposing they mean 3300 years from 2001, to be sure, you're looking at year 5301, not year 4000, so you have a little leeway to consider the question.

    Tom Hanlin
    PowerBASIC Staff

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  • Frank Ferrell
    started a topic Perpetual Calendar; Year 4000-and-beyond

    Perpetual Calendar; Year 4000-and-beyond

    Greetings --

    This query is sure to send you scrambling for your Earth Science and/or Astronomy Books.

    Is it true that the Gregorian Calendar gains one day each 4000 years? If so, it implies that there would be no February 29th in the year 4000 and every 4000 years thereafter.

    I trust than we have some PowerBasic DOS/CC/Win routines to deal with the Gregorian Calendar -- but do they deal with the 4000-year scenarios described above?

    Information about the Perpetual Calendar -- general calendar facts.

    Topics/features include -- the origins of the Gregorian Calendar // How the calendar comes "back to square" every 400 years // Was it necessary to drop those 10 days in 1582, with two never-adopted alternative methods shown // Is there a 4000-year rule? // Links to the Symmetry-454 Calendar, a radical alternative to the Gregorian Calendar // Links to other Time and Date sites // A 3000-year perpetual calendar
    Last edited by Frank Ferrell; 18 Feb 2017, 04:49 PM.