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    Re: Corrections for latitude when taking sights
    From: Brad Morris
    Date: 2019 Mar 11, 23:33 -0400
    David

    The times of sunrise and sunset are used for planning purposes, to wit:  civil twilight, when observations are turned into LoPs.

    If you know when sunset it, then civil twilight lasts for a period after that.  You can pre-plan your observations, with expected altitude and azimuth.  Ditto for sunrise, the twilight period being before that.

    The tabular values are directly comparable to the USNO values online and to the Dunlap Sunrise Sunset Computer.

    Brad

    On Mon, Mar 11, 2019, 11:17 PM David Pike <NoReply_DavidPike@fer3.com> wrote:

    There is a table for interpolating times for sunrise and moonrise relative to longitude and latitude, Nautical Almanac table xxxii.

    Is there ever a reason or need to correct for latitude, for these bodies, if either are a part of a two-body fix?  I think not but I wanted to ask.

    Steve

    Steve

    The tables on page xxxii really have little to do with sextant sights except perhaps to check upon availability of a very low Sun or Moon.  They’re not a sextant correction.  They go with the times of Sun and Moonrise (and setting), which can be found on the extreme right of any daily page.  If you notice, these are only given for every 10, 5, or 2 degrees of latitude depending upon your latitude.  If you want the time any closer than that, you must go to page xxxii to make a correction.  The fact that the tables don’t appear until page xxxii might give an indication as to how often they’re used.  They were used more in WW2 in the planning of dawn attacks, moonlight low-level (the Dambusters), and the like although to be honest, the Air Almanac tended to use graphs rather than tables.  Local authorities might use then for the regulation of street lighting.  Aircraft operating authorities might use them to record their flying into day and night hours, which might have to comply with statutory regulations.  I’m sure at least one of our contributors will come up with a good navigational use, but right now I can’t think of one. DaveP  

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