By E. G. Richards

ISBN-10: 0198504136

ISBN-13: 9780198504139

This attention-grabbing ebook totally addresses a subject of a lot common curiosity via drawing jointly a wealth of various fabric at the much-trusted (and hardly disputed) phenomenon we all know because the calendar. From the basics of astronomy to the world's old time-keeping schemes, from the improvement of the modern day calendar to the suitable calculation of what occurs whilst (as in, how does one arrive on the date for Easter Sunday?), it is a skillful but approachable dialogue of the calendar from either the ancient and modern views. Readers can even how one can practice experiments and calculations for themselves by utilizing such easy options as stargazing and straightforward arithmetic.

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Babylon c. 0167 ? 00001 corresponds to about one second. 00014 days (12 seconds) since the time of Hipparchus of Nicaea. < previous page page_33 next page > < previous page page_34 next page > Page 34 determinations and the errors in them. Modern values are obtained using accurate clocks. Improvements in timekeeping have shown that the length of the mean solar year is not quite constant; it is subject to a small secular decrease of about half a second per century. It has thus decreased by about 15 seconds during the last 3000 years.

Ptolemy, again looking south, would say that the sun and the stars rotated above the earth in a clockwise direction from east to west. All the relevant astronomical measurements on which the calendar depends had been made by the time of Copernicus in the sixteenth century. Thus to understand the history of the calendar we must learn to see the heavens as the ancients saw them. It may be helpful for us in trying to appreciate the disposition and behaviour of the heavenly bodies to take a Copernican standpoint, but to understand the calendar and the problems posed and overcome in its development we must remain Ptolemaic.

During this time it has moved a little further on in its orbit about the sun, so that an observer who was directly facing the sun at noon of one day would no longer be doing so after a complete revolution, one sidereal day; later. The earth must spin a little more before our observer is facing the sun again at the next noon. The earth moves through about 1┬░ each day in its journey round the sun, so that it must rotate about its axis this extra degree before < previous page page_24 next page > < previous page page_25 next page > Page 25 noon.

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Mapping Time : The Calendar by E. G. Richards

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