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    Re: Almanacs, theory and use.
    From: Gary LaPook
    Date: 2007 Nov 20, 11:36 -0800

    Gary LaPook writes:
    the following link had been posted on september 8th to a nomogram
    which gives you the refraction correction which is easy to use:
    On Nov 20, 11:31 am, glap...@pacbell.net wrote:
    > Gary LaPook writes:
    > Attached is a link to site that will print out a version of the
    > Nautical Almanac daily pages. For times between the tabulated values
    > to find GHA you use straight line interpolation, 15� 00' per hour for
    > the sun and planets, 14� 19' for the Moon and 15� 02.5' for Aires.
    > The "v" and "d" corrections at the bottom of the columns for the
    > planets, the top of the column for the moon and the "d" correction
    > only for the sun are also used for straight line interpolation for the
    > declinations of these bodies and for their GHA motion in excess of the
    > 15� 00' standard value for the planets. ( No "v" correction for the
    > sun.)  the actual Nautical Almanac has interpolation tables included
    > for every second of time but these are not in this online almanac but
    > are easy to compute with a calculator.
    > Also attached is a link to an online version of The American Practical
    > Navigator refrence work, go to chapter 19.
    > http://www.tecepe.com.br/scripts/AlmanacPagesISAPI.isa
    > http://www.i-DEADLINK-com/bowditch/
    > On Nov 20, 3:39 am, Isonomia  wrote:
    > > We live in Scotland and my mother lives in England, so I thought it
    > > would be  pretty simple to prove to my kids using a sextant that the
    > > world was  spherical - so I bought an EBBCO on eBay. Whilst I've
    > > proved to myself I can  use a sextant to find out where I am, I'm
    > > still to convince the children either that you can, or that you would
    > > want to.
    > > I started by using some software into which I put the time,
    > > approximate  longitude, latitude and sextant reading, and (after
    > > working out I had to  subtract half the sun's diameter) I finally got
    > > something average on our  location on average about 3 miles from our
    > > location. Unfortunately, as far  as a kid is concerned, if you have a
    > > PC, you may as well look up  google/streetmap rather than waste time
    > > with a sextant, so I need to find a  PC-less way to find out where I
    > > am.
    > > So, using a bit of trig (with some software from the web) I created my
    > > own  single-page weekly tables (the sun don't shine everyday!), giving
    > > altitude  and direction of the sun for a given location for each
    > > minute of the day.  This allows me to create a table for any given
    > > place which most children who  can add two digit numbers, and use a
    > > ruler/protractor could use by  themselves (with instructions) to plot
    > > a line giving their location (to  within 10miles I hope!), which if
    > > repeated twice in a day should give an  "exact" location.
    > > Now, I know how my "Almanac" works, but even having figures for every
    > > minute  of the day, for a known location and interpolating results for
    > > seconds, I  will still be pushing it to get tabular errors less than
    > > 1'. From what I  have been able to discern about real almanacs they
    > > contains a fraction of  this information with only hourly figures for
    > > every location in the world.  Although, I've downloaded a few
    > > worksheets to "calculate" the figures, I  can't understand how these
    > > are used (I neither have a worked example, nor do  I have an almanac,
    > > nor do I have a theoretical explanation for the tables -  but I don't
    > > see that as a fundamental problem!) Surely getting from these  figures
    > > in the Almanac to one at any time for a particular location but
    > > involve some complex trigonometry and rather hectic sinusoidal
    > > interpolations - neither of which are apparent on the worksheets!
    > > What I really want to know is how my "almanac" relates to a real
    > > almanac,  and how, could and should I make my "almanac" more like a
    > > real almanac and  still have it useable by children? I've tried
    > > searching the internet, for  any explanation of how to use an almanac
    > > (with the theoretical background) -  any help would be greatly
    > > appreciate (remembering I am not familiar with  SHA, GHA, and whilst I
    > > learnt spherical geometry at University, I'm a little  rusty)
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