AAS 199th meeting, Washington, DC, January 2002
Session 40. HAD III: Some Controversies in the History of Astronomy
Special Session Oral, Monday, January 7, 2002, 2:00-3:30pm, State

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[40.06] What a Difference a Day Makes: A History of the Date Line

I. R. Bartky (Bethesda, MD)

The so-called International Date Line represents no international agreement at all. Depicting its sweep across the Pacific Ocean from pole to pole is merely a convenient way to identify and separate the countries that use Eastern (Asiatic) dating from those governments that have adopted Western (American) dates.

There are actually two Date Lines, the other one coincident with the 180th meridian from Greenwich. On crossing that meridian, a navigator adds (or subtracts) a day to his vessel's reckoning, creating an unambiguous link to the Greenwich date. Somewhat surprisingly, this particular practice was not inaugurated by the world's navies until about 1840. Before then a navigator did not change the day and date in the ship's log until he had circumnavigated the globe--thereby making the en route reconciliation of the nautical day, the civil day, and the astronomical day subject to an additional error.

In this talk the history of the "place where the day begins" is traced. Noted are the speculations of 12th- and 14th-century scholars, as well as the bewilderment of the world's first circumnavigators on finding they had lost a day. Nineteenth-century datings in various parts of the Pacific Ocean are described, and the talk concludes with the recent extention of the Date Line by the island nation of Kiribati.

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