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    Re: Nautical Almac Question
    From: Frank Reed CT
    Date: 2006 May 31, 14:25 -0500

    "Can anyone tell me why some of the "Eqn. of  Time" entries in the Nautical
    Almanac are shaded and some are not? (A good  example is the page for June
    12, 13 and 14 where there's an example of  both).  I'm guessing that's
    related to the Equation of Time reversing  sign (maybe the shaded entries are

    Yes, it's a sign  reversal. Have you ever graphed these numbers directly from
    the almanac pages.  Maybe plot the values for the 1st and 15th of each

    I think  you'll find that the Explanation section of the commercial edition
    is 100%  identical to that in the government-issued almanacs. Go to section 18
    of the  Explanation. It's entitled "Sun and Moon" under "Auxiliary and
    Planning Data"  (maybe they should include a little link that you can click on in the
    main pages  that takes you to correct section of the explanation <g>).
    Regarding the  equation of time, the Explanation says, "The sign is positive for
    unshaded  values and negative for shaded values". Equivalently, the Sun is
    "early" when  the values are unshaded and "late" when shaded. You can confirm this
    by looking  at the Sun's GHA at 12h GMT on any date. Let's take February 10. It
    varies a bit  from year to year depending on the leap year cycle, but the EqT
    for that date is  about 14m 14s. It is shaded in the Nautical Almanac, so the
    Sun will be late to  the meridian. When you look at the Sun's GHA at noon, on
    the same date, you'll  find that it's 356d 26.5'. So it hasn't yet reached
    the Greenwich meridian  --it's "late". How long will it take to get there? Well,
    it's going to have to  cover a little more than 3.5 degrees of longitude to
    get to GHA=0. At 15 degrees  per hour, that means it will need a little more
    than 14 minutes. And that's just  what the equation of time tells us.

    42.0N 87.7W, or 41.4N  72.1W.

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