Linear action is translated to rotational as proof of the Earth’s axial spin: Léon Foucault, February 1851: attached a large pendulum in the Paris Observatory as a demonstration that the Earth did indeed rotate. As the pendulum steadily oscillates back and forth, the planet continues to spin beneath it – the proof is shown by the changing path transcribed by the pendulum itself. 1781, Charles Messier, an avid comet-hunter, published a catalogue of heavenly objects that appear to be comets but are actually stationary – the catalogue’s purpose was to document the spurious objects to avoid confusion for others. Unknown to him at the time, these celestial objects were later discovered to be galactic star clusters and nebulae, and galaxies beyond our own system, some containing billions of stars. The nearest galaxy is Andromeda, or Messier catalogue number 31, i.e., M31, whose distance Edwin Hubble found to be 2.5 million light-years from Earth. image: Comet Halley, credit:NASA

linear action becomes rotational