The speed of light is the constant speed at which light and other electromagnetic radiation travel in a vacuum. The value of the speed of light in a vacuum is equal to 299,792,458 m/s (186,282.397 mi/s), as recommended by the Committee of Data for Science and Technology on July 1999 for international use in all fields of science and technology. A commonly used approximation for the speed of light is 3.0 x 108 m/s (186,000 mi/s). The electromagnetic constant c denotes the speed of light. Light travels slower in a medium (such as glass or water) than it does in a vacuum. Since space is not a perfect vacuum, light travels through space at a very slightly lower speed and decreases somewhat more when the radiation enters, for instance, a planet's atmosphere. Light would take about 1.2 seconds to travel from the Moon to Earth, around 8.5 minutes...