Speed Of Light | History of the speed of light

We explain what the speed of light is and what it is for. Also, the story of its discovery. Its importance in different areas.

speed of light

What is the speed of light?

The speed of  light  is a  measurement stipulated by the scientific community , generally used by the fields of  science of physical and astronomical studies. The speed of light indicates the amount of distance that light travels, per unit of time .

It is essential for the study of celestial, astronomical bodies, to know how is their behavior and the transmission of electromagnetic radiation and how light is perceived by the human eye.

If we know a distance, we can know how long it takes for light to travel it. As an example, it  takes about 8 minutes and 19 seconds for light from the sun to reach Earth . The speed of light is considered to be a universal constant, invariable in  physical time and  space . Its value is 299,792,458 meters per  second  , or 1080 million kilometers per hour.

This speed is related to a unit of length that is widely used in astronomy which is the light year , which refers to the distance traveled by light in one year.

The speed of light that we have presented is what it has in a vacuum. However, light is transmitted by other means, such as water, glass, or air. Its transmission depends on certain characteristics of the media, such as electrical permissiveness, magnetic permeability, and other electromagnetic characteristics. There are then physical areas that electromagnetically facilitate its transmissibility and others that hinder it.

Understanding the behavior of light is not only important for astronomical studies, but also for understanding the physics they work with, for example satellites orbiting the Earth.


The Greeks were the first to write about the origin of light  and their  thought was that light emanated from objects and then human vision was emitted to capture it.

Until the seventeenth century , light was not considered to travel , but was conceived as an instantaneous phenomenon. However, this changed from the  observation  of eclipses. It was only  Galileo Galilei  who, by conducting certain experiments, questioned this principle of “instantaneity” of the distance that light travels.

Several experiments were carried out by different scientists, some with luck and others not, however all these physical studies in this incipient scientific era pursued the objective of measuring the speed of light even with the complications that their instruments and methods were inaccurate. and primary. Galileo Galilei was the first to carry out an experiment to measure this phenomenon , but he did not obtain results that would help to calculate the transmission time of light.

Ole Roemer was the first to attempt to measure the speed of light in 1676 with relevant success. Roemer detected, by studying the planets, from the terrestrial shadow reflected on the body of Jupiter , that the time between eclipses was shorter when the distance from the Earth decreased, and vice versa. It obtained a value of 214,000 kilometers per second, an acceptable number given the level of precision with which the distance of the planets could be measured at that time.

Then,  in 1728 James Bradley  also studied the speed of light but observing the transformation of the stars, detecting what was the  displacement  that occurred in relation to the  movement of the Earth around the Sun, from this he obtained a value of 301,000 kilometers per second .

A wide variety of methods have been used  to improve measurement accuracy, for example, in 1958 the scientist Froome reached the value of 299,792.5 kilometers per second using a microwave interferometer, the most successful. From the year 1970, the measurement improved qualitatively with the development of laser devices that have greater capacity, great stability and use cesium clocks that improve the accuracy of measurements.

Speed ​​of light in different media (medium-speed)

Empty – 300,000 km / s

Air – 2999.920 km / s

Water – 225,564 km / s

Ethanol – 220,588 km / s

Quartz – 205.479 km / s

Crown glass – 197,368 km / s

Flint glass – 186,335 km / s

Diamond – 123.967 km / s

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