Galileo Galilei Determining the Speed of Light

The speed of light was once thought to be infinite and able to travel over infinite distances instantaneously. The polymath Galileo Galilei thought this to be incorrect and had an assistant stand atop a hill 1 kilometer away whilst Galilei shone a lantern and had the assistant shine one back as soon as he recognized the opposing lantern being lit. Galilei posited that he could measure the reaction time and divide it by the distance between both parties. The experiment failed to work because a much greater distance would be required for success. During the 1670’s, the Danish astronomer Ole Roemer closely observed Jupiter and its moon Io. Roemer noticed that his predictions of where Io should be did not synchronize with its actual position and subsequently realized that because Jupiter and Earth are sometimes closer together, the travel time of light between each could take between 1 hour and 1 hour and 15 minutes. Due to this realization, Roemer was able to calculate that light coming from Jupiter’s moon Io traveled at approximately 300,000 meters per second. Today scientists can verify Roemer’s experiment by pulsing a laser beam towards mirrors left upon the moon by astronauts during the Apollo missions NASA launched in decades past to confirm that the speed of light is indeed 299,792,458 meters per second. The lasers scientists use act upon the same principal Radio Detection and Ranging or Radio Direction And Ranging (RADAR), Sound Navigation and Ranging (SONAR), and Light Detection and Ranging or Laser Imaging Detection and Ranging (LIDAR) utilizes in that they all measure objects at a distance by pinging them to approximate how fast they are traveling, and how far away they are