Download PDF by Isaac Asimov: The Clock We Live On

By Isaac Asimov

В этой книге Айзек Азимов рассказывает о том, как в древности измеряли и отсчитывали время с помощью Луны, Солнца и звезд. Автор приводит интересные факты о солнечных затмениях, изгибах часовых поясов, временах года, параллелях и меридианах. Книга предназначена для широкого круга читателей.

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The Divisions of Heaven It now becomes important in time-keeping to consider the moment at which the sun is directly overhead (or at the zenith). The Babylonians had tried to pinpoint the position of heavenly bodies in the sky, and to help themselves do so they divided the heavens by a series of imaginary lines running due north and south. The entire vault of the heavens was divided by exactly 360 such lines, equally spaced. (Why 360? nd ° 360 210· The lines that divided the sky seemed to be a series of steps down which you could go in passing from zenith to horizon.

Michigan runs the bound­ ary through Lake Michigan and Florida runs it along the Chattahoochee River. Whenever possible, nations try to keep themselves in single time zones for convenience sake. M. zone is the 7t0 East Longitude line. This cuts through the western bit of Germany and the eastern bit of France. M. zone (Central European Time). Naturally, when a nation's boundaries change, its time zone boundaries frequently change also. Only a few countries have time zone problems like those of the United States.

This was not a very accurate way of deciding. In 1731, an Englishman named John Hadley invented a de­ vice to do the job better. It is now called a sextant and consists of a curved arc, making up a sixth of a circle (the word "sextant" comes from a Latin word meaning "sixth") and marked off into 120 divisions, each division being half a degree. The sextant is equipped with two mirrors, one of which is used to sight the horizon. ) The second mirror is used to sight the sun. The result is that the angle between the two mirrors, when both are properly lined up, is just half the amount by which the sun is raised above the horizon.

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The Clock We Live On by Isaac Asimov


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