A second is defined to be exactly the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.
I don't see anything referencing any planets?
I don't see anything referencing any planets?
"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom taken as an average over 11 samples distributed throughout the earth in order to approximate the earth's inertial frame"
Seconds as used in Coordinated Universal Time are in fact defined based on planets, and earth specifically - because they use earth's inertial frame.
In principle this frequency can be measured in any inertial frame. Seconds are not defined on Earth specifically.