The speed of light in a vacuum is approximately 299,792,458 meters per second, or about 186,282 miles per second. To convert this to miles per hour, we can multiply the speed in miles per second by the number of seconds in an hour, which is 3,600.
So, the speed of light in miles per hour is approximately:
186,282 miles/second * 3,600 seconds/hour ≈ 670,616,629 miles/hour.
Now, regarding how scientists determined the precise value of the speed of light, the initial measurement was conducted by the Danish astronomer Ole Rømer in the late 17th century. Rømer studied the motion of Jupiter's moon Io and its eclipses by Jupiter. He noticed that the timing of the eclipses seemed to vary depending on the Earth's distance from Jupiter.
Rømer hypothesized that the differences in timing were due to the finite speed of light. He realized that when the Earth and Jupiter were on opposite sides of the Sun, the light from Jupiter took longer to reach Earth, causing a delay in the observed eclipse. Conversely, when Earth and Jupiter were on the same side of the Sun, the light had a shorter distance to travel, resulting in an earlier observed eclipse.
By analyzing the observed variations in timing, Rømer estimated that light took about 22 minutes to traverse the Earth's orbit, which is equivalent to a speed of about 220,000 kilometers per second. This estimation was not as precise as the current value, but it provided evidence that light had a finite speed.
Over time, more refined experiments and technological advancements allowed scientists to measure the speed of light more accurately. One significant breakthrough was the use of interferometry, which involves splitting light into two beams and recombining them to observe interference patterns. The first successful measurement using interferometry was performed by Albert A. Michelson in the late 19th century, and it provided a more precise value for the speed of light.
In modern times, the speed of light has been determined through various methods, including techniques involving lasers, atomic clocks, and electromagnetic waves. These experiments utilize a combination of time, distance, and electromagnetic properties to measure the speed of light with extremely high precision.