What is the speed of light?

We explain what the speed of light is and what this measure is for. History of its discovery. Its importance in different fields.

  1. What is the speed of light?

The speed of light is a measure stipulated by the scientific community , generally used by the fields of science of physical and astronomical studies. It serves to understand the celestial, astronomical bodies, to know what their behavior is like and the transmission of electromagnetic radiation, how light is perceived by the human eye.

The theoretical basis of the speed of light is expressed by the relation that arises between how much is the delay of the light in transferring in a vacuum from one point to another , and is measured in time .

As an example we can then say that sunlight takes approximately 8 minutes and 19 seconds to reach Earth . The speed of light is considered to be a universal constant, invariable in time and physical space. It travels 299,792,458 meters per second and 1080 million kilometers per hour.

This speed is related to another stipulated measure that is the light year, which refers to the distance traveled by the light in the time that a year lasts.

Now, the speed is transmitted by means other than the “vacuum” , its transmission depends on its electrical permittivity, its magnetic permeability, and other electromagnetic characteristics. There are then physical areas that electromagnetically facilitate its transmissibility and others that hinder it.

The understanding of the behavior of light is not less, not only for its astronomical studies, but also to understand what concerns how communications on Earth occur primarily with satellites.



  1. History of the speed of light

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

From the seventeenth century, with scientists of old age, light was not considered to travel , for them it was an instantaneous matter. This understanding was given from the observation of the 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 emerging 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 conduct an experiment measuring this phenomenon , however it did not obtain results that help calculate the light transmission time.

Ole Roemer was the first to try to measure the speed of light in 1676 with relevant success. He detected by studying the planets, the earth’s shadow reflected on Jupiter’s body, that the time between eclipses was shorter when the distance to Earth decreased, and vice versa. Of which 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.

Roemer method for measurement
(Roemer method for measurement.)

Then in the year 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, it obtained a value of 301,000 kilometers per second.

A great variety of methods have been used to improve the accuracy in the measurement, being the case in 1958 of the scientist Froome who reached the value of 299,792.5 kilometers per second by means of a microwave interferometer, the most successful in the case. 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 the measurements, this from the year 1970.

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