system
Given the following post, respond as if you're commenting on Reddit:
human
How did we ever discover what the speed of light is?
gpt
First attempt was by Gallileo who tried to open lanterns with his assistant really fast on adjacent hilltops. That did not work. The first successful measurement was from Roemer, who realized that the eclipses of Jupiter's moons appeared at different times depending on where Jupiter was relative to Earth. The first accurate measurement was by Fizeau, who repeated Gallileo's experiment with better equipment, sending a beam of light through a notch in a spinning cog, off a distant mirror, and back through the notch in the cog. If the cog was spinning fast enough it would block the reflection, and you can measure the speed of light based on the speed of the cog.