The speed of light is approximately 300,000 kilometers per second, specifically 299,792.458 km/s, which is fast enough to circle the Earth about 7.5 times in one second. Light, a form of electromagnetic wave, exhibits both wave and particle duality, with visible light wavelengths ranging from about 380 to 780 nanometers, and it travels at its maximum speed in a vacuum. The history of measuring the speed of light reflects significant scientific advancements. Galileo Galilei was the first to attempt measuring it, though unsuccessfully. In 1675, Ole Rømer calculated the speed of light by observing Jupiter's moon Io. Armand Fizeau succeeded in measuring it on Earth in the mid-19th century, and Albert Michelson's precise measurements in 1926 brought us closer to the current value. Today, laser technology allows for highly accurate measurements. The journey of understanding light's speed, once thought infinite until the 17th century, highlights the remarkable progress in science. The debate over whether light is a wave or a particle has been long and complex, involving figures like Pythagoras, Aristotle, and Newton. The wave theory gained strength in the 19th century with contributions from Fresnel and Young, and Maxwell's prediction of electromagnetic waves. In the 20th century, Einstein's quantum theory reintroduced the particle nature of light, leading to the modern understanding of light's duality, a key transition from classical physics to quantum mechanics.