- #1
Patrick Aberdeen
- 7
- 2
The SI definition of a second was originally based on 1/86 400 of a day - but the Earth's rotation is a) unsteady and b) changing so it was changed to a defined number of cycles of an atomic clock. Was there a specific day for which the atomic clock was calibrated? Put another way, why were 9 192 631 770 cycles of a Caesium atomic clock chosen as the number to define a second?