Luminosity

For a long time, astronomers believed that the distinction of the visible shine of the stars is connected only with the distance to them: the next star, the less bright it should seem. But when the distance to the stars became known, astronomers found that sometimes more distant stars have a greater visible shine. It means that the visible shine of the stars depends not only on their distance, but also from the actual force of their light, that is, from their luminosity. The luminosity of the star depends on the size of the surface of the stars and from its temperature. Star luminosity expresses its true light power compared to the power of the sun. For example, when they say that the luminosity of Sirius is equal to 17, it means that the true power of his light is greater than the power of the sun of 17 times.

Determining the luminosity of the stars, astronomers found that many stars are thousands of times brighter than the sun, for example, the luminosity of Deneba (Alpha Swan) - 9400. There are among stars that emit hundreds of thousands of times more than the sun. An example is the star, denoted by the letter S in the constellation of golden fish. It shines 1 000000 times brighter. Other stars have the same or almost the same luminosity with our Sun, for example, Altair (Alpha Eagle) -8. There are stars, the luminosity of which is expressed by thousandths, that is, their strength of light is hundreds of times less than the sun.

Color, Temperature and Stars Composition

Stars have a different color. For example, Vega and Denget - White, Chapel-hotels, and Bethelgeuse is reddish. The lower the temperature of the star, the more shorter. The temperature of the white stars reaches 30,000 and even 100,000 degrees; The temperature of yellow stars is about 6000 degrees, and the temperature of the red stars is 3000 degrees and below.

Stars consist of splitted gaseous substances: hydrogen, helium, iron, sodium, carbon, oxygen and others.

Accumulation of stars

Stars in the huge space of galaxy are quite evenly distributed. But some of them are still accumulated in certain places. Of course, and there the distances between the stars are still very high. But because of the gigantic distances, such closest stars look like star cluster. Therefore, they are so called. The most famous from star clusters are Pleiads in the constellation of the Taurus. With the naked eye in the Pleiades, you can distinguish 6-7 stars located very close to each other. The telescope is visible more than a hundred on a small area. This is one of the opposites in which the stars form a more or less separate system associated with a common movement in space. The diameter of this star cluster is about 50 light years. But even with visible tight stars in this cluster, they are actually quite far from each other. In the same constellation, surrounding its main thing - the brightest - the reddish star al-Debaran, there is another, more scattered star cluster - Giada.

Some star clusters into weak telescopes have the appearance of foggy, blurred specks. In stronger telescopes, these specks, especially to the edges, disintegrate into separate stars. Large telescopes make it possible to establish that these are especially close star clusters having a spheroid form. Therefore, such clusters got the name of the ball. Ball star clusters are now known more than a hundred. All of them are very far from us. Each of them consists of hundreds of thousands of stars.

The question of what is the world of stars seems to be one of the first questions that humanity has encountered at the dawn of civilization. Anyone, contemplating the Starry Sky, involuntarily connects the brightest stars into the simplest figures - squares, triangles, crosses, becoming the involuntary creator of their own star of the starry sky. The same path also passed our ancestors who divided the starry sky to clearly distinguishable combinations of stars called constellations. In ancient cultures, we find references on the first constellations identified with the symbols of the gods or myths that have come down to us in the form of poetic names - the Constellation of Orion, the constellation of the racing of pieces, the constellation Andromeda, etc. These names symbolized the ideas of our ancestors about eternity and the immutability of the universe, the constancy and invariance of the harmony of space.

In the universe there are stars for the power of thousands of times weaker than the sun (of which we only see the closest) in a million times brighter for him. Stars light power is comparable to the sun called her luminosity. The star that seems to us bright, may seem such or due to the fact that it is close to us, or because of the fact that although it is very far away, her true skill is very huge.

With the 20 closest stars to us only three seen with the naked eye, in from the 20 stars, which we seem bright, only three are the smallest. The brightest stars are customary to call the stars of the 1st value, and the weakest with the naked eyes visible - the stars of the 6th magnitude. The stars of the 1st magnitude brighter for the star of the 6th magnitude 100 times. The binoculars can see the stars of the 8-9th magnitude. The stars of the 1st value, especially bright, in the sky near 20, stars of the 2nd magnitude, such as the main constellations of greater bears, approximately 70, and stars who are the brightest length of the 6th magnitude, close 6000.

Visible brightness

Look at the sky at night. Most likely you will see a dozen-one and a half of very bright stars (depends on the season and your location on Earth), a few dozen stars of pleasure and many, many very dull.

The brightness of the stars is their ancient characteristicnoticed by man. In antiquity, people came up with a measure for the brightness of stars - "Star magnitude". Although it is called the "value", of course, it is not about the size of the stars, but only about their brightness perceived by the eye. Some bright stars assigned the first star magnitude. Stars that looked at a certain amount of dim in the second. Stars that looked at the same magnitude of the previous one - the third. Etc.

Please note that the brighter the star, the smaller the stellar value. The first magnitude stars are far from the brightest in the sky. It took to introduce a zero star magnitude and even negative. Fractional star magnitudes are possible. The most dull stars who sees the human eye - the stars of the sixth magnitude. In binoculars can be seen until the seventh, in the amateur telescope - to the tenth-twelfth, and the modern orbital telescope "Hubble" fingers to the thirtieth.

Here are the star values \u200b\u200bof our familiar stars: Sirius (-1.5), alpha centaur (-0.3), Bethelgeuse 0.3 (on average, because the variable). All famous stars of the big bear - the stars of the second star magnitude. The star magnitude of Venus can reach (-4.5) - well, a very bright point, if you're lucky to see, Jupiter - up (-2.9).

So they measured the brightness of stars many centuries, on the eyes, comparing stars with reference. But then impartial devices appeared, and showed out interesting fact. What is the visible star brightness? It can be defined as the number of light (photons) from this star, which falls into our eyes at the same time. So, it turned out that the scale of star values \u200b\u200bis logarithmic (like all scales based on the perception of the senses organs). That is, the difference in brightness per star magnitude is the difference in the number of photons in two and a half times. Compare, for example, with a musical sound, there is the same: the difference in height per octave is the frequency difference twice.

Measuring the visible brightness of stars in stellar values \u200b\u200bis still used in visual observations, the values \u200b\u200bof stellar values \u200b\u200bare introduced into all astronomical reference books. It is convenient, for example, to quickly evaluate and comparing the brightness of stars.

Radiation power

That brightness of stars that we see eyes depends not only on the parameters of the star itself, but also from the distance to the star. For example, a small, but close Sirius looks brighter for us than a distant supergiant Bethelgeuse.

To study stars, of course, you need to compare brightness that do not depend on the distance. (It is possible to calculate them, knowing the visible brightness of the star, the distance to it and the assessment of the absorption of light in this direction.)

At first, an absolute star magnitude was used as such a measure - the theoretical star magnitude, which will be at the star, if you place it for the standard distance in 10 parses (32 light years). But all the same for astrophysical calculations, this value is inconvenient, based on subjective perception. But it was more convenient to measure the non-theoretical visible brightness, but a very real power of the star radiation. This value was named luminosity and measured in the sun luminosities, the luminosity of the Sun is taken per unit.

For reference: Sun luminosity - 3.846 * 10 in twenty-sixth degree watts.

The range of luminosity of famous stars is huge: from thousands (and even millions) share solar to five to six million.

The luminosity of the stars known to us: Bethelgeuse - 65,000 solar, Sirius - 25 solar, alpha centaurus a - 1.5 solar, alpha centaurus B - 0.5 solar, centsamima price - 0.00006 solar.

But since we moved to the conversation about brightness to the conversation about the power of radiation, it should be noted that one is not completely connected with the other definitely. The fact is that the visible brightness is measured only in the visible range, and the stars emit far from only in it one. We know that our sun is not only shine (visible light), but also heats (infrared radiation) and causes a tan ( ultraviolet radiation), and more rigid radiation is delayed atmosphere. At the Sun, the maximum radiation accounted for exactly the middle of the visible range - which is not surprising: our eyes in the process of evolution were adjusted precisely on solar radiation; For the same reason, the sun in airless space looks absolutely white. But more cold stars, the maximum radiation is shifted into the red, or even into the infrared area. There are very cold stars, such as R Golden Fish, most of the radiation of which is in the infrared area. For more hot stars, on the contrary, the maximum radiation is shifted into a blue, purple or even ultraviolet area. Estimation of the radiation power of such stars by visible radiation will be even more erroneous.

Therefore, the concept of "bolometric luminosity" of the star is used, i.e. including radiation in all bands. Bolometric luminosity, as it is clear from the above, may differ significantly from the usual (in the visible range). For example, the usual luminosity of Bethelgeuse is 65,000 solar, and the bolometric is 100,000!

What determines the power of the star radiation?

The power of the star (which means the brightness) depends on the two main parameters: on temperature (than hot, the more energy is emitted from the area of \u200b\u200bthe area) and from the surface area (than it is more, the more energy can emit a star at the same temperature) .

It follows from this that the brightest stars in the universe should be blue hypergigiants. This is true, such stars call "bright blue variables." They, fortunately, a little and they are all very far from us (which is extremely worthless for protein life), but they include the famous "star gun", this keel and other champion of the universe in brightness.

It should be borne in mind that although bright blue variables are really the brighter famous stars (luminosity of 5-6 million solar), they are not the largest. Red hypergigiments are much more blue, but they are less bright due to temperature.

I distrace from exotic hypergigants and look at the stars of the main sequence. In principle, the processes coming in all stars of the main sequence are similar (different distribution of radiation zones and convection zones in the volume of the star, but so far the entire thermonuclear synthesis goes to the kernel, it does not play a special role). Therefore, the only parameter determining the temperature of the star of the main sequence is the mass. That's so simple: the harder, the hotter. The size of the stars of the main sequence is also determined by the mass (for the same reason, the similarity of the structure and going processes). So it turns out that the harder, the more hotter, that is, the hottest stars of the main sequence - they are the biggest. Remember the picture with visible stars? It illustrates this principle very well.

And this means that the hottest stars of the main sequence are simultaneously the most powerful (bright), and the smaller their temperature, the smaller the luminosity. Therefore, the main sequence on the Herzshprung-Russell diagram and has the form of a diagonal strip from the upper left corner (the hottest stars are the brightest) to the right lower (the smallest are the most dull).

Floodlights are smaller than fireflies

There is another rule associated with the brightness of the stars. It was displayed statistically, and then he received an explanation in the theory of the evolution of stars. The brighter the stars, the less their number.

That is, dull stars are much larger than bright. Dazzling stars of spectral class O quite a bit; spectral-class stars B noticeably more; spectral class A stars are even more, and so on. Moreover, with each spectral class, the number of stars increases exponentially. So the most numerous star population of the Universe are red dwarfs - the smallest and dull stars.

And from this it follows that our sun is far from the "ordinary" star in power, but very even decent. Such stars, as the sun, are known to be relatively small, and more powerful - and less.

How long can the star live? For a start, let's decide: Under the time of the star's life, we mean its ability to exercise nuclear synthesis. Because the "corpse of the star" can hang for a long time and after the end of the synthesis.

As a rule, the less massive star, the longer it will live. Stars with the smallest mass are red dwarfs. They can be with a mass of 7.5 to 50 percent solar. All that less massively can not make nuclear synthesis - and will not be a star. Modern models suggest that the smallest red dwarfs can shine to 10 trillion years. Compare this with our sun, the synthesis in which will last about 10 billion years - a thousand times less. After the synthesis of most hydrogen, according to the theory, the light red dwarf will become a blue dwarf, and when the remains of hydrogen will be exhausted, the synthesis in the kernel will stop, and the dwarf will become white.

Oldest stars

The oldest stars are, it turns out, those that were formed immediately after Big bang (about 13.8 billion years ago). Astronomers can appreciate the age of stars, looking at their star light - it tells them how much each element is in a star (for example, hydrogen, helium, lithium). The oldest stars, as a rule, consist mainly of hydrogen and helium, and a very small part of the mass is assigned to heavier elements.

The oldest of the observed stars is SMSS J031300.36-670839.3. About her opening reported in February 2014. Its age is estimated at 13.6 billion years, and this is still not one of the first stars. Such stars have not yet been detected, but they can accurately be. Red dwarfs, as we noted, live trillions of years, but they are very difficult to detect. In any case, even if such stars are, to look for them - as a needle in a haystack.

The most dull stars

What stars are the most dull? Before we answer this question, let's see what is "dim". The farther from the star, the dull it looks, so we just need to remove the distance as a factor and measure its brightness, or the total amount of energy emitted by the star in the form of photons, light particles.

If we restrict ourselves to the stars, which are still in the process of synthesis, then the lowest luminosity is in red dwarfs. The cold star with the lowest luminosity is currently red dwarf 2mass J0523-1403. A little less of the world - and we will fall into the kingdom of brown dwarfs, which are no longer stars.

There may still be the remains of the stars: white dwarfs, neutron stars and. How dull they can be? White dwarfs are slightly lighter, but cool for a long time. After a certain time, they turn into cold pieces of coal, practically non-emitting lights become "black dwarfs". To cool, white dwarfs need a lot of time, so they are simply not.

Astrophysics do not yet know what is happening with the substance of neutron stars when they cooled. Watching supernova in other galaxies, they may assume that several hundred million neutron stars should have been formed in our galaxy, but so far only a small part of this is fixed. The rest should have cooled so much that they became simply invisible.

What about black holes in a deep intergalactic space, in the orbit of which there is nothing? They still allocate a little radiation known as Hawking radiation, but it is not so much. Such single black holes probably glow less than the remains of stars. Do they exist? Maybe.

The brightest stars

The brightest stars also have property to be the most massive. They also have the custom of being the stars Wolf-district, which means that they are hot and merge a lot of mass in a strong star wind. The brightest stars also do not live a long time: "Live quickly, die young."

The brightest today with the star (and the most massive) is considered to be the R136A1. It was announced about her opening in 2010. This star Wolf-district with the luminosity is about 8,700,000 solar and weighing 265 times greater than our native star. Once her mass was 320 solar.

R136A1 is actually part of the tight accumulation of stars called R136. According to the floor of Crower, one of the discovers, "planets need more time to form, than such a star - to live and die. Even if there were planets, there would be no astronomers on them, because the night sky was as bright as daytime. "

The largest stars

Despite the huge mass, R136A1 is not the biggest star (size). There are many stars more, and all of them are red superdigids - the stars who were much smaller all their lives until hydrogen ended, helium began to synthesize, no temperature and expansion began. Our sun eventually expects such fate. Hydrogen will end and shine will expand, turning into a red giant. To become a red supergiant, the star needs to be 10 times more massive than our sun. The red supergiant phase is usually short, lasts only from several thousand to a billion years. This is a little in astronomical standards.

The most famous red superdgigants are Alpha Antaresa and Bethelgeuse, however, they are pretty small compared to the largest. Find the biggest red supergiant is a very fruitless idea, because the exact dimensions of such stars are very difficult to evaluate for sure. The largest must be 1500 times wider than the Sun, and maybe more.

Stars with the brightest explosions

High-energy photons are called gamma rays. They are born as a result of nuclear explosions, so individual countries launch special satellites for searching for gamma rays caused by nuclear tests. In July 1967, such satellites for the US authorship discovered a gamma ray explosion that was not caused nuclear explosion. Since then, many more such explosions have been discovered. They are usually short-lived, last from several milliseconds to a few minutes. But very bright - much brighter the brightest stars. The source is not on earth.

What causes the explosions of gamma rays? Dogado mass. Today, most assumptions are reduced to the explosions of massive stars (supernova or hypernovy) in the process of transformation into neutron stars or black holes. Some gamma bursts are caused by Magnetaras, a kind neutron stars . Other gamma bursts can be the result of a fusion of two neutron stars in one or a drop in a star into a black hole.

The coolest former stars

Black holes are not stars, but their remains are - however, they are fun to compare with the stars, since such comparisons show how incredible those and others can be.

The black hole is what is formed when the gravity of the star is quite strong to overcome all the other forces and force the star to collapse itself to the point of singularity. With nonzero mass, but zero volume such a point in the theory will have an endless density. However, infinity in our world is rare, so we simply do not have a good explanation for what is happening in the center of the black hole.

Black holes can be extremely massive. Black holes found in the centers of individual galaxies can be in tens of billions of solar masses. Moreover, the matter in the orbit of supermassive black holes can be very bright, brighter of all the stars of galaxies. Near the black hole can also be powerful jets moving almost at the speed of light.

The fastened stars

In 2005, Warren Brown and other astronomers from Harvard Smithsonian Astrophysician Center announced the opening of such a fast moving star that she flew out of the Milky Way and never return. Its official name - SDSS J090745.0 + 024507, but Brown called it "Star-Rogo".

Other rapid stars were found. They are known as hypersonic stars (Hypervelocity Stars), or super-fast stars. As of mid-2014, 20 such stars were discovered. Most of them seem to come from the center of the Galaxy. According to one of the hypotheses, a couple of closely related stars (binary system) passed next to the black hole in the center of the Galaxy, one star was captured by a black hole, and the other was thrown at high speed.

There are stars who are moving even faster. In fact, speaking in general, the farther star from our galaxy, the faster it is removed from us. This is due to the expansion of the universe, and not the movement of the star in space.

The most variable stars

Brightness of many stars hesitates, if you look at them from the ground. They are known as star variables. There are many of them: in the Galaxy Galaxy, the Milky Way is about 45,000 such.

According to Professor Astrophysics of Coals Höhle, the most variables from these stars are cataclysmic, or explosive, star variables. Their brightness can increase by factor 100 during the day, decrease, increase again and so on. Such stars are popular with amateur astronomers.

Today we have a good understanding of what is happening with cataclysmic variables. They are binary systems in which one star is usual, and the other is a white dwarf. Matter of the ordinary star falls on the accretion disk, which rotates around the white dwarf. After the mass of the disk is high enough, synthesis begins, as a result of which the brightness increases. Gradually, the synthesis is dried and the process begins again. Sometimes white dwarf collapses. Development options is enough.

The most unusual stars

Some types of stars are very unusual. They may not necessarily differ extreme characteristics like luminosions or mass, they are just strange.

Like, for example, Objects of Thorn-Allows. They are named in honor of the physicists of the Kipa Torn and Anna Zhitkov, who first assumed their existence. Their idea was that neutron Star It can become a kernel of a red giant or supergiant. The idea is incredible, but ... such an object was recently discovered.

Sometimes two big yellow stars are circling so close to each other, which is independent of the matter that is located between them, looks like a giant space peanut. There are only two such systems.

The star of Pshibulsky is sometimes given as an example of an unusual star, because its star light is different from the light of any other star. Astronomers measure the intensity of each wavelength to find out what the star consists of. It usually does not cause difficulties, but scientists are still trying to understand the spectrum of Pshibyl stars.

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Depends on two reasons: their actual brightness or the amount of light they emit, and from the distance to us. If all the stars were the same brightness, we could define their relative distance, simply measuring relative amount Lights obtained from them. The amount of light changes inversely proportional to the square of the distance. This can be seen on the attached pattern, where S depicts the position of the star, as a luminous point, and A and VVTB depict the screens placed so that each of them gets the same amount of light from the star.

If the larger screen is twice a few more than the screen A, it must be twice as long as it can get all the amount of light that falls on A. Then its surface will be 4 times more than the surface A. Hence it is clear that every fourth of the surface will receive a fourth part of the light falling on A. Thus, an eye or a telescope located in B will receive one fourth part from the star, relatively with the eye or a telescope in A, and the star will seem four times weaker.

In fact, the stars are far from equal in their actual brightness, and therefore the visible star does not give an accurate indication of its distance. Among the stars closest to us, many are very weak, many even invisible to the naked eye, meanwhile, there are stars whose distances are huge. A wonderful example of this regard is canolat, the 2nd star in brightness in all heavens.

For these reasons, astronomers are forced to limit themselves to the first case by determining the amount of light that the various stars are sent to us, or their visible shine, without taking into account their distances or valid brightness. The ancient astronomers divided all stars that can be seen on 6 classes: a class number expressing visible brightness is called the magnitude of the star. The brightest, among about 14, are called the stars of the first magnitude. The following brightness, approximately 50, are called the stars of the second magnitude. 3 times more than thirds of the third magnitude. Approximately the same progression increases the number of stars of each size to the sixth, which contains stars at the border of visibility.

Stars are found all possible degrees of brightness, and therefore it is impossible to carry out a clear boundaries between adjacent stars. Two observers can make two different estimates; one ranks a star to the second magnitude, and the other to the first; Some stars with one observer will be attributed to the 3rd value, the most, which for another observer will be shown the stars of the second magnitude. It is impossible, thus, with absolute accuracy to distribute the stars between individual values.

What is a stellar value

The concept of the values \u200b\u200bof stars can be easily obtained by each random contemplator of heaven. There are several stars of the 1st quantity in any clear evening. Examples of stars of the 2nd magnitude can serve as the 6 brush stars (big bear), the polar star, the bright stars of Cassiopeia. All these stars can be seen under our latitudes every night for a whole year. Stars 3 magnitude so much that it is difficult to choose for them examples. The brightest stars in the Pleiades of this particular size. However, they are surrounded by 5 other stars, which affects their assessment of their brightness. At a distance of 15 degrees from the Polar Star there is a beta small bear: it is always visible and different from the polar star with a reddish tint; It is located between two other stars, of which one - the 3rd values, and the other - the 4th.

Five clear visible weaker stars of Pleiald, too, all about the 4th magnitude, the fifth of the star is still freely visible by the naked eye; The 6th magnitude concludes stars, barely noticeable for good vision.

Modern astronomers, taking in general terms the system that reached them from antiquity, tried to give her great certainty. Careful studies have shown that the actual amount of light corresponding to various values \u200b\u200bvaries from one value to another almost in geometric progression; This conclusion is consistent with a well-known psychological law that the feeling changes in arithmetic progressionIf the reason producing it changes to the progression of geometric.

It was found that the middle star of the 5th size gives from 2 to 3 times more than the middle star of the 6th size, the star 4th size gives from 2 to 3 times more light than the star 5th, and so on ., Up to 2nd values. For the first magnitude, the difference is so large that you can hardly specify any average ratio. Sirius, for example, is 6 times brighter than Altair, which is usually considered a typical star first magnitude. To give accuracy to its estimates, modern astronomers have tried to reduce the difference between different values \u200b\u200bto the same measurement, namely, they assumed that the ratio of the brightness of stars of two consecutive classes is two and a half.

If the reception of the division of visible stars was accepted only for 6 separate quantities without any changes, then we would have met the difficulty in the fact that in the same class would have to attribute the stars, very different in brightness. In the same class, the stars would be superior to one another twice in brightness. Therefore, to make the results accuracy, we had to consider the class, the magnitude of the stars, as such a quantity that changes continuously - to introduce tenths and even hundredths of the values. So, we have stars 5.0, 5.1, 5.2 quantities, etc., or even we can share even smaller and talk about stars having the values \u200b\u200bof 5.11, 5.12, etc.

Star magnitude measurement

Unfortunately, there is still no other way to determine the amount of light received from the star as judging by the action of it. Two stars are considered equal when they seek equal brightness for the eye. Under these conditions, our judgment is very unreliable. Because observers tried to give more accuracy, putting the photometers into the move - tools for measuring the amount of light. But even with these instruments, the observer should be based on an estimate of the eye of the shine equality. The light of one star increases or decreases in a certain proportion until then. So far, for our eye, it will not seem equal to the light of another star; And this latter can be an artificial asterisk obtained by a flame of a candle or lamp. The degree of increase or decrease will determine the difference between the values \u200b\u200bof both stars.

When we try to firmly substantiate the dimming of the stars, we come to the conclusion that this task is quite complex. First of all, not all rays coming from the stars are perceived by us like light. But all rays, visible and invisible, are absorbed by the black surface and express their effect in heating it. Therefore the best way Measure the radiation of the star is to evaluate the heat that it sends, as it is more accurate reflects the processes occurring on the luminaire than it can make visible light. Unfortunately, heat action The star rays are so little that cannot be measured even with modern devices. So far, we must leave hope to determine the full scattering of the star and limit the only part of it, which is called light.

Consequently, if we strive for accuracy, then we must say that the light, as we understand it, maybe in essence, only in their actions on the optic nerve, and there is no other way to measure its effect, except for an eye assessment. All photometers that serve to measure the light of the stars are built so that it is possible to increase or decrease the light of one star and visually equating it to the light of another star or other source and only so evaluate it.

Star magnitude and spectrum

Difficulty of receipt exact results It also increases that the stars differ in their color. With much greater accuracy, we can make sure in the equality of two light sources when they have the same color shade than when the colors are different. Another source of uncertainty comes from what is called Purkinje phenomenon (Purkinje), by name, which first described it. He found that if we have two sources of shining one and the same brightness, but one red, and the other green, then with an increase in or decreasing in the same proportion, these sources will stop seemingly the same brightness. In other words, mathematical axiom that halves or quarters of equal values \u200b\u200bare also equal to each other, not applicable to the action of light on the eyes. When the brightness decreases, the green spot begins to seem brighter than red. If we increase the brightness of both sources, then the red begins to seem brighter green. In other words, the red rays for our vision are faster and weakened than the rays are green, with one and the same change in the actual brightness.

It is also found that this law of changing the seeming brightness does not apply consistently on all colors of the spectrum. It is true that when we go from the red to the purple end of the spectrum, yellow color goes out less quickly than red, with a decrease in brightness, and green is even less quick than yellow. But if we move from green to blue, it can already be said that the latter does not disappear as fast as green. Obviously, of all this it follows that two stars of various colors, seemingly the same bright for the naked eye, will no longer seem equal to the telescope. Red or yellow stars seem relatively brighter in the telescope, green and bluish - relatively brighter for the naked eye.

In this way, it can be concluded that, despite the significant improvement of measuring instruments, the development of microelectronics and computers, visual observations still play the most important role In astronomy, and it is unlikely that this role will decrease in the foreseeable future.