Time-stamp Semantics and Representation
this paper [Pavise 1982]. In order to simplify the present discussion we shall adopt the Gregorian calendar as our prototypical calendar. Calendar years are typically an integral number of days, yet there are not (currently) an integral number of days in any astronomically computed year. For example...
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ftciteseerx:oai:CiteSeerX.psu:10.1.1.31.5057 2023-05-15T18:22:58+02:00 Time-stamp Semantics and Representation Curtis E. Dyreson The Pennsylvania State University CiteSeerX Archives 1992 application/postscript http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.31.5057 en eng http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.31.5057 Metadata may be used without restrictions as long as the oai identifier remains attached to it. ftp://ftp.cs.arizona.edu/reports/1992/TR92-16.ps.Z text 1992 ftciteseerx 2016-01-07T22:28:16Z this paper [Pavise 1982]. In order to simplify the present discussion we shall adopt the Gregorian calendar as our prototypical calendar. Calendar years are typically an integral number of days, yet there are not (currently) an integral number of days in any astronomically computed year. For example, for the Gregorian calendar year 1985, the anomalistic year was 365:259; 641 ephemeris days, the tropical year was in the northern hemisphere's Spring and fast in its Fall; and unpredictable variations, probably caused by differing rates of rotation between the core and the mantle. The gradual slowing of the rate of rotation adds about 1.5 milliseconds to the length of a day (in comparison to other clocks) during a century. The length of a day could fluctuate by 4 milliseconds over the course of a decade due to the unpredictable variations. Finally, seasonal variations can cause changes on the order of 1.2 milliseconds in the length of a day during a year [Howse 1980]. Another factor to consider in making precise sidereal time measurements is polar wander . Polar wander is a slight circular wobble of the Earth around the North/South pole on the order of 8 meters a year. Polar wander shifts an observer's meridian by a fraction each day (recall that the observer's meridian is used to determine when the sidereal and solar days start). The size of the shift depends on the observer's latitude. The family of universal times attempts to correct for these variations. UT0 is the mean solar time for the prime meridian computed by direct astronomical observations. The prime meridian is the 0 Text South pole Unknown South Pole |
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this paper [Pavise 1982]. In order to simplify the present discussion we shall adopt the Gregorian calendar as our prototypical calendar. Calendar years are typically an integral number of days, yet there are not (currently) an integral number of days in any astronomically computed year. For example, for the Gregorian calendar year 1985, the anomalistic year was 365:259; 641 ephemeris days, the tropical year was in the northern hemisphere's Spring and fast in its Fall; and unpredictable variations, probably caused by differing rates of rotation between the core and the mantle. The gradual slowing of the rate of rotation adds about 1.5 milliseconds to the length of a day (in comparison to other clocks) during a century. The length of a day could fluctuate by 4 milliseconds over the course of a decade due to the unpredictable variations. Finally, seasonal variations can cause changes on the order of 1.2 milliseconds in the length of a day during a year [Howse 1980]. Another factor to consider in making precise sidereal time measurements is polar wander . Polar wander is a slight circular wobble of the Earth around the North/South pole on the order of 8 meters a year. Polar wander shifts an observer's meridian by a fraction each day (recall that the observer's meridian is used to determine when the sidereal and solar days start). The size of the shift depends on the observer's latitude. The family of universal times attempts to correct for these variations. UT0 is the mean solar time for the prime meridian computed by direct astronomical observations. The prime meridian is the 0 |
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The Pennsylvania State University CiteSeerX Archives |
format |
Text |
author |
Curtis E. Dyreson |
spellingShingle |
Curtis E. Dyreson Time-stamp Semantics and Representation |
author_facet |
Curtis E. Dyreson |
author_sort |
Curtis E. Dyreson |
title |
Time-stamp Semantics and Representation |
title_short |
Time-stamp Semantics and Representation |
title_full |
Time-stamp Semantics and Representation |
title_fullStr |
Time-stamp Semantics and Representation |
title_full_unstemmed |
Time-stamp Semantics and Representation |
title_sort |
time-stamp semantics and representation |
publishDate |
1992 |
url |
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.31.5057 |
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ftp://ftp.cs.arizona.edu/reports/1992/TR92-16.ps.Z |
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http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.31.5057 |
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Metadata may be used without restrictions as long as the oai identifier remains attached to it. |
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