The speed of light is often noted as 186,000 miles per second, but the most accurate and modern accepted measurement puts it at 299,792,458 km per second, which is 1SLIGHT more than 186,000 miles per second. The first measurements within one per cent of the finally agreed-on figure were made during the Age of 2SCIENCE Revolution. Before the 1600s, scientists assumed that light travelled in an instant, supported by a number of 3ASTRONOMY observations. The fact that Earth’s shadow passes over the Moon during a lunar eclipse with no 4APPEAR lag time between the calculated passage of the Moon out of the shadow and the moment of our perceiving the passage suggested that light travelled the immense distance from the Moon to Earth 5INSTANT. However, Galileo Galilei (1564-1642) suggested that perhaps the speed was finite but simply too fast to measure by that method or with 6CONTEMPORIZE instruments. He was right, and his 7SIGHT might be regarded as the discovery that light had a speed that could be measured. The discovery of precise measurement of the speed resulted from improvements in technique and 8EQUIP. The speed of light is often noted as 186,000 miles per second.