| 单词 | ephemeris time |
| 释义 | ephemeris time(ET) A time system that has a constant uniform rate as opposed to other systems that depend on the earth's rate of rotation, which has inherent irregularities. It is reckoned from an instant in 1900 (Jan 0d 12h) when the sun's mean longitude was 279.696 677 8°. The unit by which ephemeris time is measured is the tropical year, which contains 31556 925.9747 ephemeris seconds . This fundamental definition of the second was replaced in 1964 by the caesium second of atomic time |
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