we have known the speed of light,
image credit NASA/ Wikimedia Commons, light in a vacuum travels at
186,282 miles per second (299,792 kilometres per second), and in theory nothing
can travel faster than light. In miles per hour, light speed is, well, a lot:
about 670,616,629 mph. If you could travel at the speed of light, you could go
around the Earth 7.5 times in one second, but how did we find out about how
fast it travelled? back in the day, scientists believed that light was
infinitely fast; it travelled instantaneously. But 344 years ago, on November
21, 1676, a Danish astronomer named Ole Rømer disproved that. When he studied Io, one of
Jupiter’s moons, he discovered that light did not travel instantaneously, and
light had a finite speed, He was trying to figure out how long it takes Io
to orbit Jupiter in hopes of using it as a cosmic clock. He watched Io
disappear behind Jupiter and reappear on the other side. He did this over and
over every 42 hours for years, to his surprise, the timing of the eclipses was
not consistent. When Earth was closest to Jupiter, the eclipses happened 11
minutes early. Likewise, when the two planets were farthest away, the eclipses
were 11 minutes behind schedule, Rømer figured out the pattern and made an
accurate prediction for Io's eclipse on Nov. 9, 1676. Then on Nov. 21, he took
his findings to the Royal Academy of Sciences and explained that a finite speed
of light must be responsible, what an amazing piece of observation.
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