The Secret Behind White Hat
Second Definition & Meaning 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.The ground state is defined at zero magnetic field. The factor of 60 comes from the Babylonians who used a sexagesimal (base-60) numeral system. However, the Babylonians did not subdivide their time units sexagesimally . The hour had been defined by the ancient Egyptians as either 1/12 of daytime or 1/12 of nighttime, hence both varied with the seasons. Greek astronomers, for example Hipparchus and Ptolemy, defined the hour as 1/24 of a mean solar day. Sexagesimally subdividing this mean solar hour made the second 1/86,400 of a mean solar day. This current definition was adopted in 1967 when it became feasible to define the second based on fundamental properties of nature with caesium clocks. Because the speed of Earth's rotation varies and is slowing ever so slightly, a leap second is...