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25: 🎂 The Timeline of Timekeeping, Origins of Speech, and the Birthday of Birthdays

Let's Learn Everything!

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The Second of Ephemeral Time

In 1952, the International Astronomical Union redefined the second as a fraction of a year. This was known as ephemeral time and is based on the idea that 31,556,925.9747 of the tropical year of 1900 January zero at 12 hours ephemeris time is a split-second. Lewis Essen who helped develop one of the first practical usable atomic clocks called it "unusable" for scientific purposes.

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