13 October 19

Today my train-loving nephew Matt Lang turns 28! So I'm wearing steam locomotives for him. Today is also known as Train Your Brain Day! In the world of international standards, on this date in 1967, the modern definition of the second was established 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 cesium-133 atom." It's still one-3600th of an hour.