Ephemeris Second
31,556,925.974 ephemeris seconds are defined as the length of the 1900.0. This differs from the SI , which is defined in terms of vibration of a Cs atom.
ephemeris second: an obsolete definition of the second used between 1955 and 1965, based on the Earth's speed of rotation. Now replaced - see second (of time).
Ephemeris Second
The length of a tropical second (1/31,556,925.97474 of the tropical year) on 1900 January 0.5 ephemeris time. [H76]
Ephemeris Time ...
The previous is an excerpt (with the exception of the reference to "ephemeris second") from WWW version of the National Institute of Standards and Technology: Physics Laboratory's International System of Units (SI) second law of thermodynamics ...
Now replaced by the ephemeris second. mean solar time See solar time. mean square Referring to the arithmetic mean of the squares of the values under consideration, as mean-square amplitude, mean-square error.
(a) Time based on the ephemeris second. Ephemeris time is determined primarily from observations of the Moon against the background of stars, ...
After three years of comparisons with lunar observations it was determined that the ephemeris second corresponded to 9,192,631,770 cycles of the caesium resonance.
9747 ephemeris seconds and a speed of light of 299,792.5 km/s produced a light-year of 9.
 See also: Ephemeris, Second, Earth, Orbit, Total
  
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