Since ancient times, people tried to understand light, what is made of, or how fast it travels.

In 1676, the Danish astronomer Ole Rømer was the first to demonstrate that light travels at a finite speed. Rømer concluded, after analyzing Io’s motion, one of the Jupiter’s moon, that the speed of light is about 250,000 kilometers per second.

After centuries of increasing the accuracy of the measurements, in 1975 experiments have shown that the speed of light is 299,792,458 meters per second (about 300,000 kilometers per second or 186,000 miles per second).

Apollo 11 Extravehicular Activity (EVA) on the lunar surface. (Credit: Wikimedia)

Currently, the fastest speed ever achieved by a human being was on May 26, 1969. During reentry in the Earth’s atmosphere, the Apollo 10 Lunar Module reached speeds of 24,791 miles per hour or 39,897 kilometers per hour.

At that speed you could go around the Earth in about an hour or reach the Moon and back in about 19 hours. As for travelling at the speed of light, you would be able to go around the world about seven and a half times in just one second or reach the Moon and back in two and a half seconds.

What’s more interesting is that it takes from tens of thousands to millions of years for a photon to get from the core to the surface of the Sun. From there it needs an average of 8 minutes and 20 seconds to reach the Earth or an average of 5 hours and 28 minutes to reach Pluto.

Einstein’s special theory of relativity, published in 1905 in a paper titled “On the Electrodynamics of Moving Bodies”, tied mass and energy together in the famous, simple and fundamental equation E = mc2. This explains why nothing with mass can travel faster than light – at or near light speed, any extra energy you put into an object does not make it move faster but just increases its mass.

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