Set off with us on a journey from Earth to the Moon at the speed of light. Distance? 384 thousand kilometers
The speed of light it makes 7.5 revolutions per second around the Earth: in practice 0.13 seconds per orbit. But how long does it take to reach the Moon? Consider that a photon travels at 300,000 kilometers per second which, although it may be an enormous value, becomes very slow in the Universe. From Earth to the Moon our photon would take about 1.255 seconds (surface to surface). In the following video by Dr. James O’Donoghue, the distance between the Earth and the Moon, along with the dimensions, are scaled and shown what would happen practically in real time.
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How it was measured
We owe the Danish astronomer Ole Rømer the determination of the speed of light which is equal to 300,000 km/s. But who tried it first? Obviously Galileo Galilei: he realized that it had a finite value but did not have sufficient means to calculate it. It was Rømer himself who determined the speed of light in 1676, observing the motion of Io, one of Jupiter’s moons, while working at the royal observatory in Paris directed at the time by Giovanni Domenico Cassini. Io completes a complete orbit around Jupiter in 1.76 days: but Rømer realized that the time taken by the moon was not always the same and depended on the Earth-Io distance. Our planet moving away from the system in some periods of the year, it determined this difference.
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