PHYS 103 Study Guide - Midterm Guide: Sidereus Nuncius, Semi-Major And Semi-Minor Axes, De Revolutionibus Orbium Coelestium
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Originally 1 ten-millionth the distance from north pole (of earth) to equator. Then a distance between two fine lines engraved on a platinum-iridium bar. (1960): 1,650,763. 73 wavelengths of a orange-red light emitted by atoms of kr-86 in a gas discharge tube. (1983, current standard): the length of path traveled by light during a time interval of 1/299,792,458 seconds. The only things that can travel that fast are massless electromagnetic radiation. Low-mass things can travel in excess of 99% the speed of light. C represents the value being of constant celerity (speed) Originally, the time for a pendulum (1-m long) to swing from one side of path to other. Later, a fraction of mean solar day. (1967): the time taken by 9,192,631,770 vibrations of a specific wavelength of light emitted by a cesium-133 atom. Originally based on the mass of a cubic decimeter of water.
