Earth to sun   en

History of the Speed of Light

  • Galileo Galilei

    Galileo Galilei
    Galileo came up with an experiment to measure light's velocity. He and his assistant took a shuttered lantern and they stood on hilltops one mile apart. Galileo flashed his lantern and as soon as his assistant saw Galileo's light he was supposed to flash his light. Galileo would then time how long it took before he saw the light from the other hilltop. This experiment didn't allow Galileo to come up with an estimated speed of light.
  • Ole Roemer

    Ole Roemer
    Ole Roemer was the first person to actually calculate the speed of light. Until this time, scientists assumed that light was either too fast to measure or infinite.
  • Ole Roemer's Experiment

    Ole Roemer's Experiment
    Roemer measured the speed of light by timing eclipses of Jupiter's moon Io. In this figure, S is the Sun, E1 is the Earth when closest to Jupiter (J1) and E2 is the Earth about six months later, on the opposite side of the Sun from Jupiter (J2). When the Earth is at E2, the light from the Jupiter system has to travel an extra distance represented by the diameter of the Earth's orbit. This causes a delay in the timing of the eclipses. Roemer measured the delay and, knowing approximately the diame
  • James Bradley

    James Bradley
    The aberration of light is an astronomical phenomenon which produces an apparent motion of celestial objects about their real locations. It was discovered and later explained by the third Astronomer Royal, James Bradley, in 1725, who attributed it to the finite speed of light and the motion of Earth in its orbit around the Sun.
  • Armand Fizeau

    Armand Fizeau
    Fizeau set up an experiment where he placed a light five and a half miles away from a mirror. In front of the light he placed a wheel with toothed edges. When the light would shine, it would pass between the gaps between two teeth. The mirror would reflect the ray of light back and it would shine through the next gap between the teeth. With this experiment, Fizeau could then estimate the speed of light from the speed at which the toothed wheel was moving. Fizeau predicted the speed of light was
  • Albert Michelson

    Albert  Michelson
    Michelson's experiment consists of a half-transparent mirror oriented at a 45° angle to a light beam so that the light is divided into two equal parts, one which is transmitted to a fixed mirror and the other which is reflected to a movable mirror. The half-transparent mirror has the same effect on the returning beams, splitting each of them into two beams. Thus, two diminished light beams reach the screen, where interference patterns can be observed by varying the position of the movable mirror
  • Heirich Heinz

    Heirich Heinz
    Hertz generated some electromagnetic waves in his labratory. He measured the speed of the waves and came up with a very familiar number. He calculated the speed of light to be 300 000 kilometers per second.