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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: no leap second coming in December
From: Frank Reed CT
Date: 2004 Jul 29, 13:46 EDT
George H wrote:
"I know that delta-T has fluctuated significantly in the past, but this time
there seems to have been a rather sudden increase in spin speed, by quite a
large amount. What could be the cause of this rather dramatic change? "

The recent changes in delta-t are not that dramatic. Here's some code I use for delta-t for the period 1750 to 2050 (gives a value for each decade year so for example DTtable(2) is 15 seconds for the year 1770):
DTtable(0) = 12    '1750
DTtable(1) = 14
DTtable(2) = 15
DTtable(3) = 16
DTtable(4) = 16
DTtable(5) = 13.1  '1800
DTtable(6) = 12
DTtable(7) = 11.6
DTtable(8) = 7.1
DTtable(9) = 5.4
DTtable(10) = 6.8  '1850
DTtable(11) = 7.7
DTtable(12) = 1.4
DTtable(13) = -5.5
DTtable(14) = -6
DTtable(15) = -2.8 '1900
DTtable(16) = 10.4
DTtable(17) = 21.1
DTtable(18) = 24.0
DTtable(19) = 24.3
DTtable(20) = 29.1 '1950
DTtable(21) = 33.1
DTtable(22) = 40.2
DTtable(23) = 50.5
DTtable(24) = 56.9
DTtable(25) = 63.1 '2000
DTtable(26) = 69
DTtable(27) = 76
DTtable(28) = 83
DTtable(29) = 90
DTtable(30) = 97   '2050
DTtable(31) = 104

Except for the speculative extrapolation for future t, this table is taken from Meeus' "Astronomical Algorithms". Note that there are changes in the 19th century that are quite large and that they are both positive and negative.

Frank R
[X] Mystic, Connecticut
[ ] Chicago, Illinois Browse Files

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