In a paper published in 1865, James Clerk Maxwell proposed that light was an electromagnetic wave and, therefore, travelled at speed c. Progressively more accurate measurements of its speed came over the following centuries. Ole Rømer first demonstrated in 1676 that light travels at a finite speed (non-instantaneously) by studying the apparent motion of Jupiter's moon Io. The speed of light can be used in time of flight measurements to measure large distances to extremely high precision. In computing, the speed of light fixes the ultimate minimum communication delay between computers, to computer memory, and within a CPU. When communicating with distant space probes, it can take minutes to hours for signals to travel from Earth to the spacecraft and vice versa. Starlight viewed on Earth left the stars many years ago, allowing humans to study the history of the universe by viewing distant objects. For many practical purposes, light and other electromagnetic waves will appear to propagate instantaneously, but for long distances and very sensitive measurements, their finite speed has noticeable effects. Īll forms of electromagnetic radiation, including visible light, travel at the speed of light. According to the special theory of relativity, c is the upper limit for the speed at which conventional matter or energy (and thus any signal carrying information) can travel through space. The speed of light c is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second 186,000 miles per second 671 million miles per hour). and, theoretically, about 78 billion years to reach us from the edge of the observable universe (this is actually longer ago than the 13.7 billion year age of the universe, because the continued expansion of space has significantly increased the distance the light from these early objects has had to travel).The speed of light in vacuum, commonly denoted c, is a universal physical constant that is important in many areas of physics.59 million years to reach us from the Virgo Cluster, the nearest large galaxy cluster.2,500,000 to reach us from the Andromeda Galaxy, our next nearest galaxy (and the most distant object visible to the naked eye, although only as a barely perceptible smudge). 26,000 years to reach us from the center of our Milky Way galaxy.4.37 years to reach us from Alpha Centauri, the nearest star system to the Solar System (Alpha Centauri is therefore said to be 4.37 light years away).0.0000033 seconds to travel 1 kilometer.As a comparison, sound waves travel at a paltry 343.14 meters per second (about 1,235 kilometers per hour), almost a million times slower than light waves, and the fastest military airplane, the SR-71 Blackbird, can fly at about 980 meters per second (about 3,500 kilometers per hour). Light travels at exactly 299,792,458 meters per second in a vacuum (about 300,000 kilometers per second or just over 1 billion kilometers per hour). (Original Source N/A: /%7Ewudka/Physics7/Notes_www/node65.html) The reasoning used by Rømer in 1675 to determine the speed of light Random Facts: HOW FAST DOES LIGHT TRAVEL? A Few Random Facts Where in the universe is the Earth? How fast are we traveling through space? How fast does light travel? How far is it to space, the Moon, the Sun, the stars, etc? How many stars are there? How does the Sun shine? What different types of stars are there? What is the human body (and the Earth, the Sun, the Universe) made of? How many molecules/atoms are there in each cubic meter? What if the history of the universe were squeezed into the period of one year? What are the coldest and the hottest objects in the universe? What is the electromagnetic spectrum? What is a planet? What is a dwarf planet? Why do the planets orbit the Sun?
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