The speed of light in a vacuum- the absolute value of the propagation velocity electromagnetic waves in a vacuum. In physics, it is denoted Latin letter c.
The speed of light in a vacuum is a fundamental constant, independent of the choice of inertial reference system.
By definition, it is exactly 299 792 458 m / s (approximate value of 300 thousand km / s).
According to the special theory of relativity, is maximum speed to disseminate any physical interactions transmitting energy and information.

How the speed of light was determined

For the first time, the speed of light was determined in 1676 O. K. Roemer by changing the time intervals between eclipses of Jupiter's satellites.

It was installed in 1728 by J. Bradley, based on their observations of the aberration of the light of the stars.

In 1849 A. I. L. Fizeau was the first to measure the speed of light by the time it took light to pass a precisely known distance (base); Since the refractive index of air differs very little from 1, ground measurements give a value that is very close to s.
In Fizeau's experiment, a beam of light from a source S, reflected by a semitransparent mirror N, was periodically interrupted by a rotating toothed disk W, passed the base MN (about 8 km) and, reflected from mirror M, returned to the disk. Falling on the prong, the light did not reach the observer, and the light that fell into the gap between the prongs could be observed through the eyepiece E. The time the light passed through the base was determined from the known speeds of rotation of the disk. Fizeau obtained the value c = 313300 km / s.

In 1862 J. B. L. Foucault realized the idea expressed in 1838 by D. Arago, using a rapidly rotating (512 rev / s) mirror instead of a toothed disk. Reflecting from the mirror, the beam of light was directed to the base and upon returning it again fell on the same mirror, which had time to turn through a certain small angle. With a base of only 20 meters, Foucault found that the speed light is equal to 29800080 ± 500 km / s. The schemes and basic ideas of the experiments of Fizeau and Foucault were repeatedly used in subsequent works to determine p.

Bernard Jeff

1. A naval officer measured the speed of light

In the spring of 1879, the New York Times reported: “A new bright Star... Ensign maritime service, a graduate of the Naval Academy in Annapolis, Albert A. Michelson, who is not yet twenty-seven years old, has achieved outstanding success in the field of optics: he measured the speed of light. " In an editorial entitled Science to the People, the Daily Tribune wrote: “The local newspaper of Virginia City, a mining town in far-flung Nevada, proudly reports:“ Lt. Albert A. Michelson, son of Samuel Michelson, owner of a haberdashery shop in our city, attracted the attention of the whole country with a remarkable scientific achievement: he measured the speed of light. "

The speed of light has been thought and argued about since ancient times, but before Michelson, only three scientists (they were all French) managed to measure it using earthly means. This was a very old and very difficult problem. Before Michelson, no one on the American continent even tried to stage this difficult experiment.

However, over the past centuries, philosophers and scientists have accumulated a fairly extensive store of information about the properties of light. For 300 years BC, in the days when Euclid created his geometry, Greek mathematicians already knew a lot about light. It was known that light propagates in a straight line and that when reflected from a flat mirror, the angle of incidence of the beam is equal to the angle of reflection. Ancient scientists were well aware of the phenomenon of light refraction. It consists in the fact that light, passing from one medium, such as air, to a medium of a different density, such as water, is refracted.

Claudius Ptolemy, an astronomer and mathematician from Alexandria, compiled tables of measured angles of incidence and refraction, but the law of refraction of light was discovered only in 1621 by the Dutch mathematician from Leiden Willebrord Snellius, who found that the ratio of the sines of the angle of incidence and the angle of refraction is constant for any two media different density.

Many ancient philosophers, including the great Aristotle and the Roman statesman Lucius Seneca, thought about the causes of the rainbow. Aristotle believed that the color spectrum appears as a result of the reflection of light by water droplets; Seneca adhered to approximately the same opinion, believing that clouds consisting of particles of moisture are a kind of mirror. One way or another, man throughout his history has shown an interest in the nature of light, as evidenced by the myths, legends, philosophical disputes and scientific observations that have come down to us.

Like most ancient scientists (excluding Empedocles), Aristotle believed that the speed of light is infinitely great. It would be surprising if he thought differently. After all, such a tremendous speed could not be measured by any of the then existing methods or instruments. But even in later times, scientists continued to reflect and argue about this. About 900 years ago, the Arab scientist Avicenna suggested that, although the speed of light is very high, it must be finite. This was the opinion of one of his contemporaries, the Arab physicist Algazen, who was the first to explain the nature of twilight. Neither one nor the other, of course, had the opportunity to confirm their opinion experimentally.

Galileo's experience

Such disputes could go on indefinitely. To resolve the issue, a clear, irrefutable experience was needed. The first to embark on this path was the Italian Galileo Galilei, striking in the versatility of his genius. He suggested that two people, standing on the tops of hills at a distance of several kilometers from each other, give signals using flashlights equipped with shutters. This idea, later realized by the scientists of the Florentine Academy, he expressed in his work "Conversations and Mathematical Proofs Concerning Two New Branches of Science Relating to Mechanics and Local Movement" (published in Leiden in 1638).

Galileo has three interlocutors talking. The first, Sagredo, asks: “But what kind and what degree of speed should this movement be? Should we consider it instantaneous or occurring in time, like all other movements? " Simplicio, a retrograde, immediately replies: "Everyday experience shows that the light from the flame of shots is imprinted in our eye without any loss of time, as opposed to the sound that reaches the ear after a considerable period of time." Sagredo, with good reason, objects: "From this well-known experience, I can not draw any other conclusion, except that the sound reaches our ears at long intervals of time than light."

Here Salviati (expressing Galileo's opinion) intervenes: “The little evidence of these and other similar observations made me think of some way to make sure that the illumination, i.e. the spread of light is really instantaneous. The experience I came up with is as follows. Two faces each hold a fire, enclosed in a lantern or something similar, which can be opened and closed with a movement of the hand in full view of the companion; standing opposite each other “at a distance of several cubits, the participants begin to practice closing and opening fire in full view of the companion in such a way that as soon as one notices the light of the other, he immediately opens his own ... I was able to produce it only at a short distance - less than one mile - why I could not be sure whether the appearance of the opposite light really occurs suddenly. But if it does not happen suddenly, then, in any case, with extreme speed. "

The means at Galileo's disposal then, of course, did not allow this issue to be resolved so easily, and he was fully aware of this. The controversy continued. Robert Boyle, the famous Irish scientist who gave the first correct definition chemical element, believed that the speed of light is finite, and another genius of the 17th century, Robert Hooke, believed that the speed of light was too high to be determined experimentally. On the other hand, the astronomer Johannes Kepler and the mathematician Rene Descartes took the point of view of Aristotle.

Römer and the moon of Jupiter

The first breach in this wall was made in 1676. It happened to a certain extent by accident. The theoretical problem, as has happened more than once in the history of science, was solved in the course of a purely practical task. The needs of the expanding trade and the growing importance of navigation prompted the French Academy of Sciences to engage in the refinement of geographical maps, which, in particular, required more reliable way definitions geographic longitude... Longitude is determined fairly in a simple way- by a time difference of two different points the globe, but then they still did not know how to make a sufficiently accurate watch. Scientists have proposed using some celestial phenomenon that is observed every day at the same hour to determine the Paris time and time on board the ship. According to this phenomenon, a navigator or geographer could set his watch and find out the Paris time. Such a phenomenon, visible from anywhere on the sea or on land, is the eclipse of one of the four large moons of Jupiter discovered by Galileo in 1609.

Among the scientists dealing with this issue was the young Danish astronomer Ole Roemer, who four years earlier had been invited by the French astronomer Jean Picard to work at the new Parisian observatory.

Like other astronomers of the time, Roemer knew that the period between two eclipses of the satellite closest to Jupiter varies throughout the year; observations from the same point, separated by a period of six months, give a maximum difference of 1320 seconds. These 1320 seconds were a mystery to astronomers, and no one could find a satisfactory explanation for them. There seemed to be some kind of relationship between the orbital period of the satellite and the position of the Earth in orbit relative to Jupiter. And now Roemer, having thoroughly checked all these observations and calculations, unexpectedly simply solved the riddle.

Roemer assumed that 1320 seconds (or 22 minutes) is the time it takes for light to travel the distance from the Earth's orbiting position to Jupiter to the position farthest from Jupiter, where the Earth is six months later. In other words, the additional distance that light reflected from Jupiter's satellite travels is equal to the diameter of the Earth's orbit (Fig. 1).

Rice. 1. Roemer's line of reasoning.
The orbital period of the satellite closest to Jupiter is approximately 42.5 hours. Therefore, the satellite had to be obscured by Jupiter (or leave the eclipse band) every 42.5 hours. But during six months, when the Earth moves away from Jupiter, eclipses were observed each time with an ever greater delay in comparison with the predicted dates. Roemer came to the conclusion that light does not propagate instantaneously, but has a finite speed; therefore, it takes more and more time for it to reach the Earth, as it, moving in orbit around the Sun, moves away from Jupiter.

At the time of Röhmer, the diameter of the Earth's orbit was considered to be approximately 182,000,000 miles (292,000,000 km). Dividing this distance by 1320 seconds, Roemer found the speed of light to be 138,000 miles (222,000 km) per second.

At first glance, it may seem that it is not much merit to obtain a numerical result with such an error (almost 80,000 km per second). But think about what Roemer did achieve. For the first time in the history of mankind, it was proved that movement, considered infinitely fast, is accessible to knowledge and measurement.

Moreover, from the very first attempt, Roemer obtained the value correct order... If we take into account that scientists are still working on clarifying the diameter of the Earth's orbit and the timing of the eclipse of Jupiter's satellites, then Roehmer's error will not be surprising. Now we know that the maximum lag of a satellite eclipse is not 22 minutes, as Roemer thought, but approximately 16 minutes 36 seconds, and the diameter of the Earth's orbit is approximately equal not to 292,000,000 km, but 300,000,000 km. If we introduce these amendments into Röhmer's calculation, it turns out that the speed of light is 300,000 km per second, and this result is close to the most accurate figure obtained by scientists of our time.

The main requirement for a good hypothesis is to make correct predictions based on it. Based on the speed of light calculated by him, Roemer was able to accurately predict some eclipses several months in advance. For example, in September 1676, he predicted that in November Jupiter's moon would appear approximately ten minutes late. The tiny satellite did not disappoint Roemer and appeared at the predicted time with an accuracy of one second. But the Parisian philosophers were not convinced even by this confirmation of Roemer's theory. However, Isaac Newton and the great Dutch astronomer and physicist Christian Huygens came out in support of the Dane. And some time later, in January 1729, the English astronomer James Bradley in a slightly different way came to the same conclusion as Roemer. There was no room for doubt. Roemer put an end to the popular belief among scientists that light travels instantly, regardless of distance.

Roemer proved that, although the speed of light is very high, it is nevertheless finite and can be measured. However, while giving credit for Roemer's achievement, some scholars were still not entirely satisfied. The measurement of the speed of light by his method was based on astronomical observations and took a long time. They also wanted to carry out the measurement in the laboratory by purely terrestrial means, without leaving our planet, so that all the conditions of the experiment were under control. The French physicist Maren Marsenne, a contemporary and friend of Descartes, was able to measure the speed of sound thirty-five years ago. Why can't you do the same with light?

First measurement by earthly means

However, the solution of this problem had to wait almost two centuries. In 1849, the French physicist Armand Hippolyte Louis Fizeau came up with a rather simple way. In fig. 2 shows a simplified diagram of its installation. Fizeau directed a light beam from a source into a mirror V, then this ray was reflected on the mirror A... One mirror was installed in Suresnes, in the house of Fizeau's father, and the other in Montmartre in Paris; the distance between the mirrors was approximately 8.66 km. Between the mirrors A and V a gearwheel was placed, which could be rotated at a given speed (principle of a stroboscope). The teeth of the spinning wheel interrupted the light beam, breaking it into pulses. In this way, a chain of short flashes was sent.

Rice. 2. Fizeau installation.
174 years after Roemer calculated the speed of light from observations of eclipses of the moon of Jupiter, Fizeau constructed a device to measure the speed of light under terrestrial conditions. Gear C broke a beam of light into flashes. Fizeau measured the time it took for light to travel the distance from C to the mirror A and back, equal to 17.32 km. The weakness of this method was that the moment of the greatest brightness of the light was determined by the observer by eye. Such subjective observations are not accurate enough.

When the gear was stationary and in its original position, the observer could see the light from the source through the gap between the two teeth. Then the wheel was set in motion at an ever-increasing speed, and there came a moment when the light pulse, passing through the gap between the teeth, returned, reflected from the mirror A, and was delayed by a barb. In this case, the observer saw nothing. With further acceleration of the rotation of the cogwheel, the light reappeared, became brighter and, finally, reached its maximum intensity. The cogwheel used by Fizeau had 720 teeth, and the light reached its maximum intensity at 25 revolutions per second. Based on these data, Fizeau calculated the speed of light as follows. The light travels the distance between the mirrors and back while the wheel turns from one gap between the teeth to another, i.e. in 1/25 × 1/720, which is 1/18000 of a second. The distance traveled is equal to twice the distance between the mirrors, i.e. 17.32 km. Hence the speed of light is 17.32 * 18,000, or about 312,000 km per second.

Foucault's refinement

When Fizeau announced the result of his measurement, scientists questioned the reliability of this colossal figure, according to which light reaches from the Sun to the Earth in 8 minutes and can fly around the Earth in an eighth of a second. It seemed incredible that a person could measure such a tremendous speed with such primitive instruments. Does light travel more than eight kilometers between Fizeau mirrors in 1/36000 of a second? Impossible, many said. However, the figure obtained by Fizeau was very close to the result of Röhmer. This could hardly be a coincidence.

Thirteen years later, with skeptics still doubting and ironic, Jean Bernard Léon Foucault, the son of a Parisian publisher who at one time was preparing to become a doctor, determined the speed of light in a slightly different way. He worked with Fizeau for several years and thought a lot about how to improve his experience. Instead of a cogwheel, Foucault used a rotating mirror.

Rice. 3. Foucault's installation.
After some improvements, Michelson used this device to determine the speed of light. In this device, the gear wheel (see Fig. 2) is replaced by a rotating flat mirror C... If the mirror C motionless or very slowly turns, light is reflected on a translucent mirror B in the direction indicated by the solid line. When the mirror rotates rapidly, the reflected beam shifts to the position indicated by the dotted line. By looking through the eyepiece, the observer could measure the displacement of the beam. This measurement gave him twice the value of the angle α, i.e. the angle of rotation of the mirror while the beam of light was coming from C to the concave mirror A and back to C... Knowing the speed of rotation of the mirror C, distance from A before C and the angle of rotation of the mirror C during this time, it was possible to calculate the speed of light.

Foucault enjoyed a reputation as a talented researcher. In 1855 he was awarded the Copley Medal of the Royal Society of England for his experience with the pendulum, which was proof of the rotation of the Earth on an axis. He also built the first gyroscope suitable for practical use... The replacement in Fizeau's experiment of a cogwheel with a rotating mirror (this idea was proposed back in 1842 by Dominico Arago, but was not implemented) made it possible to shorten the path traveled by a light beam from more than 8 kilometers to 20 m. A rotating mirror (Fig. 3) deflected the return beam at a small angle, which made it possible to carry out the necessary measurements to calculate the speed of light. The result obtained by Foucault was 298,000 km / sec, i.e. about 17,000 km less value obtained by Fizeau. (In another experiment, Foucault placed a tube filled with water between reflecting and rotating mirrors to determine the speed of light propagation in water. It turned out that the speed of light propagation in air is greater.)

Ten years later, Marie Alfredo Cornu, professor of experimental physics at the Paris Higher polytechnic school, returned to the cogwheel again, but it already had 200 teeth. Cornu's result was close to the previous one. He got a figure of 300,000 km per second. This was the case in 1872, when the young Michelson, a final year student at the Naval Academy in Annapolis, was asked at an optics exam to talk about Foucault's apparatus for measuring the speed of light. It never occurred to anyone then that in physics textbooks, from which future generations of students would study, Michelson would be allotted much more space than Fizeau or Foucault.

Long before scientists measured the speed of light, they had to work hard to define the very concept of "light". One of the first to think about this was Aristotle, who considered light to be a kind of mobile substance spreading in space. His ancient Roman colleague and follower Lucretius Carus insisted on the atomic structure of light.

TO XVII century formed two basic theories of the nature of light - corpuscular and wave. Newton was among the adherents of the first. In his opinion, all light sources emit the smallest particles. In the process of "flight" they form luminous lines - rays. His opponent, the Dutch scientist Christian Huygens, insisted that light is a kind of wave motion.

As a result of centuries of disputes, scientists have come to a consensus: both theories have the right to life, and light is visible to the eye spectrum of electromagnetic waves.

A bit of history. How the speed of light was measured

Most ancient scientists were convinced that the speed of light is infinite. However, the results of the studies of Galileo and Hooke admitted its limit, which was clearly confirmed in the 17th century by the outstanding Danish astronomer and mathematician Olaf Roemer.


He made his first measurements by observing the eclipses of Io, the satellite of Jupiter at the moment when Jupiter and the Earth were located with opposite sides relative to the sun. Roemer recorded that as the Earth moved away from Jupiter at a distance equal to the diameter of the Earth's orbit, the lag time changed. The maximum value was 22 minutes. As a result of calculations, he received a speed of 220,000 km / s.

50 years later, in 1728, thanks to the discovery of aberration, the English astronomer J. Bradley "refined" this figure to 308,000 km / s. Later, the speed of light was measured by French astrophysicists Francois Argo and Leon Foucault, who received 298,000 km / s at the "exit". An even more accurate measurement technique was proposed by the creator of the interferometer, the famous American physicist Albert Michelson.

Michelson's experiment in determining the speed of light

The experiments lasted from 1924 to 1927 and consisted of 5 series of observations. The essence of the experiment was as follows. On Mount Wilson in the vicinity of Los Angeles, a light source, a mirror and a rotating octahedral prism were installed, and after 35 km, on Mount San Antonio, a reflecting mirror was installed. First, the light through the lens and slit fell on a prism rotating with the help of a high-speed rotor (at a speed of 528 rps).

The participants in the experiments could adjust the speed of rotation so that the image of the light source was clearly visible in the eyepiece. Since the distance between the peaks and the rotation frequency were known, Michelson determined the value of the speed of light - 299796 km / s.

Scientists finally decided at the speed of light in the second half of the 20th century, when masers and lasers were created, characterized by the highest stability of the radiation frequency. By the beginning of the 70s, the measurement error dropped to 1 km / s. As a result, on the recommendation of the XV General Conference on Weights and Measures, held in 1975, it was decided to assume that the speed of light in a vacuum is now equal to 299792.458 km / s.

Is the speed of light achievable for us?

It is obvious that the exploration of the distant corners of the Universe is unthinkable without spaceships flying at great speed. Desirable at the speed of light. But is this possible?

The light speed barrier is one of the consequences of the theory of relativity. As you know, an increase in speed requires an increase in energy. The speed of light would require almost infinite energy.

Alas, the laws of physics are categorically against this. At speed spaceship at 300,000 km / s, particles flying towards it, for example, hydrogen atoms, turn into a deadly source of powerful radiation equal to 10,000 sievert / s. This is about the same as being inside the Large Hadron Collider.

According to scientists at Johns Hopkins University, while in nature there is no adequate protection from such a monstrous cosmic radiation. Erosion from the effects of interstellar dust will complete the destruction of the ship.

Another problem with light speed is time dilation. At the same time, old age will become much more prolonged. The visual field will also undergo a curvature, as a result of which the trajectory of the ship will pass, as it were, inside a tunnel, at the end of which the crew will see a shining flash. Absolute pitch darkness will remain behind the ship.

So in the near future, mankind will have to limit their high-speed "appetites" 10% of the speed of light. This means that the closest star to the Earth - Proxima Centauri (4.22 light years) will take about 40 years to fly.


The Universe participates in experiments

The method by which Le Verrier captured the imagination of scientists. The movement of Neptune was closely monitored and soon found such significant differences between the observed and theoretical orbits of the new star that this could only be explained by the existence of another planet located behind Neptune!

On February 18, 1930, the young astronomer Clyde Tombaugh of the Lovell Observatory in America finally discovered (at a distance almost three times the radius of the orbit of Neptune) new planet Solar system named Pluto... Tombaugh thereby confirmed the calculations of the famous theoretical astronomers Percival Lovell and William Pickering.

Indeed, as the famous French optician and astronomer François Arago said, "... mental eyes can replace powerful telescopes ...".

There are nine major planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. Between Mars and Jupiter, there are a large number of small planets called asteroids. However, astronomers continue to search for new planets.

Theoretical forecasts have shown that so far for displacement celestial bodies in the solar system is not affected by the attraction of distant stars and other planetary systems of our galaxy. The sun should "attract" small and major planets... The gravitational force of the Sun extends over a distance 200 thousand times greater than the path from the Earth to the Sun!

It cannot be that in such a vast space there were no dense celestial bodies, although so far the search for the tenth planet of the solar system with the help of the most powerful modern telescopes has not been crowned with success ...

As we can see, celestial mechanics invariably confirms the laws of earthly mechanics, derived by Newton. The motion of celestial bodies, as it turned out back in the time of Newton, allows not only to check the law universal gravitation, but also gives researchers a wonderful way to determining the speed of light.

It is strange that Galileo did not guess about such a method, offering for this purpose only the experiment with lanterns. Two people stand at a great distance from each other with lanterns in their hands and mark the time it takes for the light of a suddenly lit lantern to cover the distance between them. The experiment, unfortunately, is completely impracticable due to the too high speed of light ...

How was the speed of light measured?

In September 1676, a young Dane Olaf Roemer, who worked at the Paris Observatory, presented to the French Academy of Sciences a report in which he described how, using the rotation of the Earth around the Sun, one can determine the speed of light.

Römer, during his research, observed the movement of one of Jupiter's moons. The time of the complete revolution of the satellite around the planet was strictly constant and well known to astronomers. Roemer noted: if the Earth, while rotating around the Sun, is at the point of its orbit farthest from Jupiter, then astronomers observe the satellite's entry into Jupiter's shadow 22 minutes later than at the moment when the Earth is closest to Jupiter. Roemer guessed the reason for the strange phenomenon - the light needs 22 minutes to cover the distance from the nearest point to the point of the Earth's orbit farthest from Jupiter. Knowing the time that light spends on this, and calculating the diameter of the Earth's orbit, we can easily determine the speed of light!

This was probably one of the first cases in the history of science when a scientist used the Universe as a giant natural laboratory ...

Römer obtained values ​​of the speed of light, which are one and a half times less modern meanings this value. But one can hardly blame him for this: we know with what instruments his great contemporary Galileo Galilei measured time.

The astronomical method of measuring the speed of light has been widely used by physicists for three centuries after the observations and calculations of Roehmer. Now the generally accepted value of the speed of light in a vacuum, equal to 299.79 thousand kilometers per second.

In the 19th century, they learned to determine the speed of light on Earth. American physicist Albert Michelson achieved high perfection in these experiments. His complex massive device with many mirrors lengthening the path of light was placed on a stone slab with an area of ​​1.5 m 2 and a thickness of 30 cm. To avoid the slightest possible shock of the device, the plate support was filled with mercury.

Michelson found that the speed of light does not depend on the direction of the beam, the propagation of light is not affected by the rotation of the Earth. Exceptional thoroughness of Michelson's experiments, achieved in early XIX century high accuracy in determining true meaning the speed of light, perhaps, prompted Albert Einstein to consider the speed of light in a vacuum itself high speed which is possible in Nature. This idea is one of the most important postulates of the theory of relativity created by Einstein - the most general modern theory motion, into which Newton's laws were included as a special case.

It is known that the speed of light in a vacuum is finite and amounts to ≈300,000 km / s. All of this data is based on modern physics and all modern space theories. But until recently, scientists were convinced that the speed of light is infinite, and we instantly see what is happening in the farthest corners of space.

People began to think about what light is in ancient times. The light from the flame of a candle, instantly spreading throughout the room, flashes of lightning in the heavens, observation of comets and other cosmic bodies in the night sky gave the feeling that the speed of light is infinite. Indeed, it is difficult to believe that, for example, looking at the Sun, we observe it not in its present state, but as it was about 8 minutes ago.

But some people still questioned the seemingly well-established truth about the infinity of the speed of light. One of these people was Isaac Bengman, who in 1629 tried to conduct an experiment to determine the final speed of light. He had, of course, no computers, no high-sensitivity lasers, no high-precision clocks at his disposal. Instead, the scientist decided to make an explosion. Having filled the container with an explosive, it different distance set large mirrors from her and asked the observers to determine in which of the mirrors the flash from the explosion would appear first. Considering that in one second, light is able to circumnavigate the earth 7.5 times, you can guess that the experiment ended in failure.

A little later, the notorious Galileo, who also questioned the infinity of the speed of light, proposed his experiment. He put his assistant with the lantern on one hill, and he himself stood with the lantern on the other. When Galileo lifted the lid from his lantern, his assistant immediately lifted the lid from the opposite lantern. Of course, this experiment also could not be crowned with success. The only thing Galileo could have guessed was that the speed of light is much faster than human reaction.

It turns out that the only way out was to participate in the experiment of bodies far enough from the Earth, but which could be observed with the help of telescopes of that time. Jupiter and its moons are such objects. In 1676, astronomer Ole Roemer tried to determine the longitude between different points on geographic map... To do this, he used a system for observing the eclipse of one of Jupiter's moons - Io. Ole Roemer conducted his research from an island near Copenhagen, while another astronomer, Giovanni Domenico Cassini, observed the same eclipse from Paris. Comparing the time of the beginning of the eclipse between Paris and Copenhagen, scientists determined the difference in longitude. For several years in a row, Cassini observed the moons of Jupiter from the same location on Earth and noticed that the time between eclipses of the satellites gets shorter when the Earth is closer to Jupiter and longer when the Earth is farther from Jupiter. Based on his observations, he suggested that the speed of light is finite. It was absolutely the right decision, but for some reason, Cassani soon backtracked on his words. But Roemer took the idea with enthusiasm, and even managed to draw up clever formulas that take into account the diameter of the Earth and the orbit of Jupiter. As a result, he calculated that it took light about 22 minutes to cross the diameter of the Earth's orbit around the Sun. His calculations were wrong: according to modern data, light travels this distance in 16 minutes and 40 seconds. If Ole's calculations were accurate, the speed of light would be 135,000 km / s.

Later, based on Röhner's calculations, Christian Huyens substituted more accurate data for the diameter of the Earth and the orbit of Jupiter into the formulas. As a result, he got the speed of light equal to 220,000 km / s, which is much closer to the correct value.

But not all scientists have calculated the correct hypothesis of the finiteness of the speed of light. Scientific debate continued until 1729, when the phenomenon of light aberration was discovered, which confirmed the assumption that the speed of light was finite and made it possible to more accurately measure its value.

It is interesting: modern scholars and historians come to the conclusion that, most likely, the formulas of Roemer and Huyens were correct. The error was in the data on the orbit of Jupiter and the diameter of the Earth. It turns out that it was not two astronomers who were wrong, but the people who provided them with information about the orbit and diameter.

Main photo: depositphotos.com

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