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    Re: The Nautical Day
    From: Henry Halboth
    Date: 2004 Feb 7, 11:40 -0500

    Historically navigators and seamen in general considered the day as
    beginning at noon, which was marked by the upper transit of the sun, and
    all ships' work was calculated over the interval from transit to transit.
    Many older navigational pubs treat this to varying degrees of detail.
    Refer to Dutton, 1934 edition, where it is stated as follows ........
    "Formerly navigators considered the day as beginning at the instant the
    sun crossed the upper branch of the meridian, i.e., at noon. Mean time,
    with the beginning of the day at that instant, is called astronomical
    time. Navigators now use the instant of transit of the sun across the
    lower branch or the meridian .... etc."
    I'm not too sure as to how this came to be called the Nautical Day.
    At least until comparatively recently, a vessel's day's work was still
    calculated from noon to noon, based, however, on noon at Greenwich, plus
    or minus the ZD - somewhat of a carry-over from the old system.
    On Fri, 6 Feb 2004 20:01:37 +0000 George Huxtable
    > I've recently been reading "The Arctic Whaling Journals of William
    > Scoresby
    > the Younger, vol 1." ed. C. Ian Jackson, pub. The Hakluyt Society
    > 2003.
    > This covers his first three voyages as master, in 1811, 1812, and
    > 1813.
    > Scoresby made 12 such voyages, and it is intended that future
    > volumes will
    > cover the rest.
    > Scoresby was involved in the "Greenland Whaling", which took place
    > each
    > year to the East of Greenland, near to the Western coast of
    > Spitzbergen.
    > While in port, and when making his way out to sea, Scoresby's
    > journal was
    > written up according to the calendar day, as we're all familiar
    > with,
    > starting at ending at midnight.
    > Most of us are aware that until the 1920s, time in the Nautical
    > Almanac was
    > in terms of the Astronomical Day, which started at the noon of the
    > calendar
    > day having the same date. The Astronomical Day was therefore 12
    > hours after
    > the corresponding calendar day.
    > However, as soon as Scoresby had got to sea, he started to write his
    > journal (which was effectively his log) according to a different
    > timescale
    > altogether, the Nautical Day. This started and ended at the noon
    > the calendar day with the same date.
    > I had heard of the Nautical Day before, but the only reference to it
    > I have
    > been able to find is in Bowditch vol 2 (1981) in which he says-
    > "Nautical Day- Until January 1, 1925, a day that began at noon, 12
    > hours
    > earlier than the calendar day, or 24 hours earlier than the
    > astronomical
    > day of the same date."
    > I had dismissed the Nautical Day as something of an early American
    > aberration, but Scoresby has shown me that view was wrong.
    > So why on Earth would mariners use yet another timescale, differing
    > from
    > both civil time and astronomical time? Were some almanacs, perhaps,
    > printed
    > with Nautical Time as their argument? How prevalent was this use of
    > Nautical Time, how far back did it go, when in practice did it end?
    > Was it
    > common within the whaling community generally?
    > In the 18th century voyages of exploration I have read, I don't
    > remember
    > seeing any references to Nautical Time at all. So it doesn't seem to
    > have
    > been part of the exploring navigator's baggage, in the half-century
    > preceding Scoresby.
    > Can anyone offer any light on this matter, or provide any references
    > that
    > mention it?
    > George.
    > ================================================================
    > contact George Huxtable by email at george@huxtable.u-net.com, by
    > phone at
    > 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1
    > Sandy
    > Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    > ================================================================

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