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GMHA = Universal Time − Offset, the Greenwich Mean Hour Angle of the mean (fictitious) Sun. Here time and angle are quantities that are related by factors such as: 2 π radians = 360° = 1 day = 24 hours. The difference, EOT, is measurable since GHA is an angle that can be measured and Universal Time, UT, is a scale for the measurement of time.
On a prograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the Sun and a certain distant star are both overhead. At time 2, the planet has rotated 360° and the distant star is overhead again (1→2 = one sidereal day). But it is not until a little later, at time 3, that the Sun is overhead again (1→3 = one solar day). More simply, 1→2 is a complete ...
The single standard watch of 4 hours (two double hours) was divided into 60 time-degrees (ush). One double hour had 30, and one complete stellar day, 360 (12 times 30). [ 19 ] This assignment was the creation of the 360-degree circle, as the degree went from being a time division to an angular distance of rotation.
"Babylonian hours" divide the day and night into 24 equal hours, reckoned from the time of sunrise. [25] They are so named from the false belief of ancient authors that the Babylonians divided the day into 24 parts, beginning at sunrise. In fact, they divided the day into 12 parts (called kaspu or "double hours") or into 60 equal parts. [26]
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One kè was usually defined as 1 ⁄ 100 of a day until 1628, though there were short periods before then where days had 96, 108 or 120 kè. [7] A kè is about 14.4 minutes, or 14 minutes 24 seconds. In the 19th century, Joseph Charles François de Rey-Pailhade endorsed Lagrange’s proposal of using centijours, but abbreviated cé , and ...
The arithmetic mean (or simply mean or average) of a list of numbers, is the sum of all of the numbers divided by their count.Similarly, the mean of a sample ,, …,, usually denoted by ¯, is the sum of the sampled values divided by the number of items in the sample.
As an example, if a gas-powered pump can drain a pool in 4 hours and a battery-powered pump can drain the same pool in 6 hours, then it will take both pumps 6·4 / 6 + 4 , which is equal to 2.4 hours, to drain the pool together. This is one-half of the harmonic mean of 6 and 4: 2·6·4 / 6 + 4 = 4.8. That is, the appropriate ...