Burnlaw, Northumberland: Sleepless at 4am and studying our sole satellite, I’m struck by the remarkable journey light takes to make it into our view
I have a habit, if I wake some nights, to get up and go downstairs to read. Last night was noteworthy because I could see the moon as a mere horn repeatedly swallowed then reborn from the passing clouds. Through binoculars, however, I could make out the other portion of the whole lunar sphere as a sort of ill-lit inference.
It was Leonardo da Vinci who first suggested that this shadow part of the crescent moon is visible because of sunlight rebounding off the Earth and then re-transmitted on our one satellite. It was wonderful to imagine that the energy received here, even as I stood gazing, was re-presented out there a little over a second later. That is because light travels at a speed per second roughly similar to our distance from the moon (the respective figures are about 300,000 km/sec and an average 384,400 km).
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