5 ms·

A second is one 86400th of a rotation of our home-planet

• rpearl 3y ago
  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?
  • throwaway09223 3y ago
    Well, a second is more specifically defined as: "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.
    • rpearl 3y ago
      The SI definition of a second, available at https://www.bipm.org/documents/20126/41483022/SI-Brochure-9.pdf/fcf090b2-04e6-88cc-1149-c3e029ad8232 https://www.bipm.org/documents/20126/41483022/SI-Brochure-9...., section 2.3.1, does not reference our particular planet, nor any particular means of measurement, nor does it have to. In principle this frequency can be measured in any inertial frame. Seconds are not defined on Earth specifically.