Laurinkienė, Nijolé. "Saulės ratų ir laivo mitiniai vaizdiniai: šviesulys paros cikle (Mythical Images of the Solar Carriage and Ship: the Heavenly Body in the Course of an Astronomical Day)". In: Tautosakos darbai t. 54, p. 13-25. .
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Up to late 1805 the Royal Navy used three days: nautical, civil (or "natural"), and astronomical. For example, a nautical day of 10 July, would commence at noon on 9 July civil reckoning and end noon on 10 July civil reckoning, with PM coming before AM. The astronomical day of 10 July, would commence at noon of 10 July civil reckoning and ended at noon on 11 July. The astronomical day was brought into use following the introduction of the Nautical Almanac in 1767, and the British Admiralty issued an order ending the use of the nautical day on 11 October 1805. The US did not follow suit until 1848, while many foreign vessels carried on using it until the 1880s.
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A report was submitted to the "Transactions of the Royal Society of Canada," dated 10 May 1894; on the "Unification of the Astronomical, Civil and Nautical Days"; which stated that: :civil day- begins at midnight and ends at midnight following, :astronomical day- begins at noon of civil day and continue until following noon, and :nautical day- concludes at noon of civil day, starting at preceding noon.
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"Saulės ratų ir laivo mitiniai vaizdiniai: šviesulys paros cikle (Mythical Images of the Solar Carriage and Ship: the Heavenly Body in the Course of an Astronomical Day)". In: Tautosakos darbai t. 54, p. 13-25. . In a Croatian fairy tale (Fisherman Plunk and his Wife), the Dawn-Maiden (Zora-djevojka) arrives from the sea in a silver boat with golden oars, and sails back to Buyan, the mysterious island where she dwells.
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This agreed with the civil Greenwich Mean Time used on the island of Great Britain since 1847. In contrast astronomical GMT began at mean noon, i.e. astronomical day X began at noon of civil day X. The purpose of this was to keep one night's observations under one date. The civil system was adopted as of 0 hours (civil) 1 January 1925. Nautical GMT began 24 hours before astronomical GMT, at least until 1805 in the Royal Navy, but persisted much later elsewhere because it was mentioned at the 1884 conference.
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The astronomical day had begun at noon ever since Ptolemy chose to begin the days for his astronomical observations at noon. He chose noon because the transit of the Sun across the observer's meridian occurs at the same apparent time every day of the year, unlike sunrise or sunset, which vary by several hours. Midnight was not even considered because it could not be accurately determined using water clocks. Nevertheless, he double-dated most nighttime observations with both Egyptian days beginning at sunrise and Babylonian days beginning at sunset.
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Although two delegates, including Sandford Fleming, proposed the adoption of standard time by all nations, other delegates objected, stating that it was outside the purview of the conference, so neither proposal was subjected to a vote. Thus the conference did not adopt any time zones, contrary to popular belief. Regarding resolution 6: Great Britain had already shifted the beginning of the nautical day from noon, twelve hours before midnight, to midnight in 1805, during the Battle of Trafalgar. The astronomical day was shifted from noon, twelve hours after midnight, to midnight effective by a resolution of the newly formed International Astronomical Union.
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In the 19th century, an idea circulated to make a decimal fraction ( or ) of an astronomical day the base unit of time. This was an afterglow of the short-lived movement toward a decimalisation of timekeeping and the calendar, which had been given up already due to its difficulty in transitioning from traditional, more familiar units. The most successful alternative is the centiday, equal to 14.4 minutes (864 seconds), being not only a shorter multiple of an hour (0.24 vs 2.4) but also closer to the SI multiple kilosecond (1, 000 seconds) and equal to the traditional Chinese unit, kè.
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This location was chosen because by 1884 two-thirds of all nautical charts and maps already used it as their prime meridian. The conference did not adopt Fleming's time zones because they were outside the purpose for which it was called, which was to choose a basis for universal time (as well as a prime meridian). During the period between 1848 and 1972, all of the major countries adopted time zones based on the Greenwich meridian. In 1935, the term Universal Time was recommended by the International Astronomical Union as a more precise term than Greenwich Mean Time, because GMT could refer to either an astronomical day starting at noon or a civil day starting at midnight.
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The Nautical Almanac began in 1866 to include a Julian day for every day in the year of issue. The Connaissance des Temps began in 1871 to include a Julian day for every day in the year of issue. The French mathematician and astronomer Pierre-Simon Laplace first expressed the time of day as a decimal fraction added to calendar dates in his book, ', in 1823.Laplace 1823 Other astronomers added fractions of the day to the Julian day number to create Julian Dates, which are typically used by astronomers to date astronomical observations, thus eliminating the complications resulting from using standard calendar periods like eras, years, or months. They were first introduced into variable star work in 1860 by the English astronomer Norman Pogson, which he stated was at the suggestion of John Herschel.Pogson 1860 They were popularized for variable stars by Edward Charles Pickering, of the Harvard College Observatory, in 1890.Furness 1915. Julian days begin at noon because when Herschel recommended them, the astronomical day began at noon.
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