The speed of light was first accurately determined by a Danish astronomer named Ole Rømer in the 17th century. Rømer made his observations while studying the moons of Jupiter.
Rømer noticed that the observed time intervals between the eclipses of Jupiter's moon Io seemed to vary depending on the Earth's position in its orbit around the Sun. He hypothesized that this variation was due to the finite speed of light.
To compute the speed of light, Rømer used the following steps:
Observations: Rømer carefully observed the eclipses of Jupiter's moon Io over an extended period of time. He recorded the time intervals between successive eclipses.
Earth's Orbit: Rømer realized that the observed time intervals appeared to be shorter when the Earth was closer to Jupiter and longer when the Earth was farther away. He concluded that this discrepancy was due to the time it takes for light to travel the additional distance when the Earth is farther from Jupiter.
Calculation: Rømer calculated the average time it took for light to travel the diameter of Earth's orbit around the Sun. This average distance is known as the astronomical unit (AU). He estimated the AU to be approximately 140 million kilometers.
Speed of Light: Using his estimated AU and the observed time intervals, Rømer calculated the speed of light to be about 225,000 kilometers per second.
It's important to note that Rømer's initial calculation was not extremely accurate, as his estimation of the AU had some errors. However, his work laid the foundation for subsequent scientists to refine the measurement of the speed of light using different experimental techniques and advancements in technology. Over time, the speed of light has been measured with increasing precision, leading to the currently accepted value of approximately 299,792 kilometers per second.