Google marked the 340th anniversary of the determination of the speed of light by making a fascinating Doodle today. As the adage ‘Quick as lightning’ signifies the incredible speed of light and the question of determining the speed of light some 400 years ago must have been a quixotic quest for the best scientific brains of that time.
In 1675, Ole Roemer, a Danish astronomer observed that the times of the eclipses of the moons of Jupiter depends upon the relative positions of Jupiter and Earth. Ole found that if the distance between Jupiter and Earth was smaller, the orbit of Jupiter’s moons appeared to speed up and if the distance was larger they seemed to slow down.
Ole tried to find out the cause of this anomaly and concluded that it the obvious change must be due to the extra time light took to travel when Earth was more distant from Jupiter. Adding up the diameter of earth’s orbit he deduced that the speed of light was 200,000 km/s. We now know that this is not accurate, but considering the basic tools and assumptions of that time, Ole had achieved something incredible.
Like his predecessor Galileo Roomer had to suffer at the hands of disbelievers and the church. His work was not accepted by the Royal Observatory in Paris. However only after Christiaan Huygens and Isaac Newton started supporting his conclusions, it started gaining importance. Nearly two decades after his death, his work was finally confirmed by the English astronomer James Bradley in 1728 discovered the speed of light as 295,000,000 meters per second.
In 1849 the French physicist, Fizeau using a rapidly rotating toothed wheel was able to find the speed of light as 313,300 Km/s. Another French scientist Leon Foucault using the same method as Fizeau but with a rotating mirror was able to find the speed of light more accurately at 299,796 Km/s. Today according to the US National Bureau of Standards, the speed of light is 299792.4590 ± 0.0008 km/sec