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The reduction of Heures définitives to a uniform system and to the mean pole of the epoch

Bulletin Horaire series H number 2 page 43

Other web pages about Bulletin Horaire

Bulletin Horaire was the regular publication of the Bureau International de l'Heure (BIH, International Time Bureau). Nicolas Stoyko served at and ran BIH for four decades, and his wife Anna Stoyko also served there. Before they retired in 1965 they summarized 42 years of data published by BIH. See here for more views of their summary data.

From inception the BIH was tasked with the difficult problem to make sense of observations of time from around the world and try to combine those into an improved estimate of what time it had been. The data were monstrously heterogeneous.

Nicolas Stoyko joined the BIH in 1926 and by 1931 he had created an algorithm for combining the heterogeneous data into a "mean observatory". Starting with 1931 the BIH published Heure définitive of the mean observatory as the best estimate of what time it had been and how much each of the contributing observatories had deviated from that mean. The calculation of the mean observatory was performed using all of the data for a calendar year. As observatories, equipment, people, and worldwide events changed, the mean observatory varied from one year to the next. This means that the final tabulated values of Heure définitive for each year could be in a different reference system than any other year.

At various points in the history of the BIH the Bulletin Horaire published tables of the estimated systematic offsets between the tabulations of Heure définitive in different years. In 1964 Anna Stoyko reviewed the tabulations of Heure définitive for each year from 1931 through 1963 and published tables required to calculate the systematic offsets.

The BIH 1962 system for Heure définitive

Note that even after the advent of atomic chronometers there were still shifts over a range of 5 ms between the time systems of one year and another.

BIH 1962 system offsets
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Steve Allen <sla@ucolick.org>
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