Wolfgang Korsus Dipl.-Ing.NT, Astrophysiker
Website : wolfgang.korsus.net
Speed of ligbht…b
So Galilei continued and he made an experiment himself with a helper. This one had to move a little further away and then cover a lamp up and down. Now Galilei tried to measure how long it took for him to see that. Of course he noticed that the light spreads faster than the sound, but at the same time it was clear to him, in order to determine the speed exactly, certainly larger distances were necessary. We suspect that these are possible only in astronomical ranges and questions arise…..
By these two points of view arise :
Is the speed of light finite, and if yes, what is its value ?
The answer to the first point of view followed, but it came some decades later from one Ole Rømer. A really highly gifted man from Aarhus in Denmark.
This man had studied mathematics, physics and astronomy in Copenhagen and he was married. A true „Jack of all trades.“ He also „worked“ for the French King Louis XIV on the design of the fountains of Versailles, there also began his career as an astronomer. I will comment on this work later. After his successful stay in France, Rømer returned to Copenhagen as a so-called „royal court mathematician“. Here, too, he was creatively active. He introduced the first Danish system of weights and measures and the Gregorian calendar. He even attained the post of director of the Copenhagen police, and in this capacity he had the first street lighting installed there.
A true jack of all trades!
Back to Paris and astronomy…and that brings us back to the astronomer Rømer. We know he was a confidant of the astronomer Giovanni Domenico Cassin and he was very closely involved with the planet Jupiter.
The largest of all planets and fifth in distance from the Sun, this one had a moon called Io. It circled Jupiter every 42 hours and this was in contrast to the 28 days, because our moon needs these for its earth orbit.
This again led to the always perceivable multiplicity of Io eclipses (that is an eclipse, thus an eclipse of a celestial body by the occultation of another) at every position of the earth in its orbit around the sun; I have represented the explaining geometry in the next illustrations. A determination now obtained was justified by a timetable. This showed the gentlemen all times for the observed disappearance of Io behind Jupiter. Also the times between two eclipses were ascertainable.
Cassini’s surprising observation was that the beginning of an eclipse was delayed ; thus increasingly more and more, the farther Earth and Jupiter were apart. He kept pondering, not quite sure about the „light“ and its movement. His thoughts began to suspect something …!?the light might need some time to reach us; he dropped the thought.
But Rømer took it up again, combined it with a number of different measurements, extrapolated the results and was of the opinion that the time difference
between the point of greatest distance from Earth and Jupiter (a) and that of least distance (b) was about 22 minutes. He then concluded that the speed of light is finite and the 22 minutes is just the time it takes for light to traverse the diameter of the Earth’s orbit around the Sun.
Ole Rømer thus used the constellation to determine the speed of light.
He also solved the second part of the initial question, namely to determine the actual value of the speed of light. For this it belonged to know this certain size of the earth’s orbit around the sun. What distance did the light cover in these certain 22 minutes?
Because this distance, one divides by 22 minutes, that would result then in the speed of light.
Information which was useful and necessary to be able to say something to the topic speed of light was apparently already available at that time. they were based on the measurements of Cassini. Later more to it. But a numerical value was shown in 1675, that took place only two years after Ole Rømer’s results. This time it was the Dutch physicist Christiaan Huygens.
Kepler, in turn, had himself noted in his third law of planetary motions that the orbital period of a planet around the Sun is determined by its distance from the Sun. From this it was possible to determine the relative solar distances of the planets, and it was found that the distance of Mars from the Sun was one and a half times the Earth-Sun distance.
So now some astronomical distance in earthly measures was needed, because finally a real longitude should be determined. Let’s call the enterprise a scientific „calibration“. This became a task for Cassini and his collaborator Jean Richer. They determined completely independently of each other at the same time the position of Mars in front of the fixed star background. One, namely Cassini in Paris and Richer in Guiana.
What had these two built up with it ? Yes, first of all an „angle“ and secondly a distance or better distance on this planet – the 4000 km between Paris and Guayana
It showed thereby a distance, namely between Mars and the earth orbit, so about the 73 mill. kilometers.Additionally the distance earth – sun, approx. 146 mill. kilometers. This Christiaan Huygens was an important Dutch physicist, mathematician and astronomer. now he divided the double of this distance, thus the diameter of the earth orbit, by Rømers 22 minutes …….and received a speed of light.
The value corresponded then to 220,000 kilometers per second.
The result, or better this value obtained more than three hundred years ago was not simply taken out of the air by the associated scientists. It was a result of a combination of logic, abstraction and the simplest measurements. I would certainly call it one of the greatest achievements of natural science. If you look at this value more closely, you come to the remarkable conclusion: the value is only 25% below today’s precision result, of 299 792.458 km/s, which was measured with radio signals between space satellites.
According to this, the light of the sun must indeed pass through the interspace before it reaches the earth, and this is what Empedocles imagined already two thousand years ago. So light flies through the empty space, but what exactly flies there ? Next question, what moves there with 300,000 kilometers per second?
Questions usually have it in such a way that they lead on a remarkable event. This happens in the inanimate and partly also in our animate world. It is the „electromagnetism“. But it is to be stated beforehand electricity and magnetism appeared as two completely different natural events at that time.
The appearance of electricity within the visible world was known already for a long time. The lightnings e.g. were considered from anger of the gods, the amber rubbing with cat fur, and still many examples more. So the name „elektron“ (Greek for amber) already originated.
But it is hardly to be believed approx. 1500 years passed before one could bring all these phenomena into a connection with the electricity. And from today’s point of view one may say, only the last hundred years electricity has fundamentally changed or even enriched our human life ?
Also magnetism seemed to be of a very explainable and simpler nature at first. Thousands of years ago, the first compass was discovered in China and used for navigation. In ancient Greece, Thales of Miletus described this effect, and since the „stones“ in question there came from a province called Magnesia, he called them magnetic.
Electricity and magnetism became part of the actual natural science less than three hundred years ago, because two kinds of electricity were discovered, purely arbitrarily called positive / negative. Both could be generated by rubbing, for example, and each kind could exist by itself. When two balls with different „charges“ were prepared, unlike ones attracted, while like ones repelled – in both cases with a mysterious force that acted across the distance of separation. In France in 1785, Charles Augustin de Coulomb showed that this force has a very similar form to Newton’s gravity. In both cases, it falls off with the square of the distance. In the case of electricity, its strength is determined by the product of charges; in the case of gravity, by that of masses. However, in the case of electricity there is both attraction and repulsion, while gravity does not know this, it always remains attractive.
Let us let the in a small framework still something more about electricity and magnetism from the research box to the air…..
First the charges, completely independently of each other they can exist and likewise behaves their production. Magnets fall there somewhat from the row, they have two opposite poles, as known, a „north pole“ and a „south pole“.
Positive and negative charges can exist independently of each other and can also be generated independently of each other. Magnets, on the other hand, are rather strange. They have two opposite poles, a „north pole and a south pole“. So what happens when you put two of them next to each other ?…North and South attract, but equal and equal repel each other. Also the possibility to isolate one is missing.
And if you cut a magnet in two, you get two new magnets. If one cuts a magnet, one receives two new, in each case again with north and south pole.
Also the method to get a monopole has not been achieved by any physicist until today. It is important to mention that the force between two magnets is slightly weaker than the force between two charges. It is the combination of attraction and repulsion, since both poles always come into play. But the force is again a form of invisible action at a distance.
Both electric and magnetic forces have a strange ability that is also noticeable in gravity…….They can act over distances without showing any apparent connection. ..and this makes us wonder how such a thing is possible. Is there perhaps after all an invisible medium, which fills the whole space and in this way provides the missing connection?
Michael Faraday, a British physicist was one of the first to give an answer to this question. Better is probably suggested…he meant that every charge is surrounded by an electric force field. It has star-shaped lines of force and these radiate accordingly in all directions. Ultimately, this field reacts to the presence of other charges, from same way and opposite towards.
Now still another, let us say strange connection was added. A Christian Ørsted in Copenhagen stated electricity and magnetism occur together.
Next Part 7 c