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If you look at the starry sky, it immediately catches your eye that the stars differ sharply in their brightness - some shine very brightly, they are easily visible, others are difficult to distinguish with the naked eye.
Even the ancient astronomer Hipparchus proposed to distinguish the brightness of stars. The stars were divided into six groups: the brightest belong to the first group - these are stars of the first magnitude (abbreviated as 1m, from the Latin magnitudo - magnitude), weaker stars - to the second magnitude (2m) and so on up to the sixth group - barely visible to the naked eye stars. The magnitude characterizes the brilliance of a star, that is, the illumination that a star creates on earth. The brightness of a 1m star is 100 times greater than that of a 6m star.
Initially, the brightness of the stars was determined inaccurately, by eye; Later, with the advent of new optical instruments, the luminosity began to be determined more precisely and less bright stars with a magnitude greater than 6 became known. (The most powerful Russian telescope - a 6-meter reflector - allows you to observe stars up to magnitude 24.)
With the increase in measurement accuracy, the advent of photoelectric photometers, the accuracy of measuring the brightness of stars increased. Star magnitudes began to be denoted by fractional numbers. The brightest stars, as well as planets, have zero or even negative magnitude. For example, the Full Moon Moon has a magnitude of -12.5, while the Sun has a magnitude of -26.7.
In 1850, the English astronomer N. Posson derived the formula:
E1/E2=(5v100)m3-m1?2.512m2-m1
where E1 and E2 are the illuminations created by the stars on the Earth, and m1 and m2 are their magnitudes. In other words, a star, for example, of the first magnitude is 2.5 times brighter than a second magnitude star and 2.52=6.25 times brighter than a third magnitude star.
However, the magnitude value is not enough to characterize the luminosity of an object; for this, it is necessary to know the distance to the star.
The distance to an object can be determined without physically reaching it. It is necessary to measure the direction to this object from the two ends of the known segment (basis), and then calculate the dimensions of the triangle formed by the ends of the segment and the distant object. This method is called triangulation.
The larger the basis, the more accurate the measurement result. The distances to the stars are so great that the length of the basis must exceed the dimensions the globe otherwise the measurement error will be large. Fortunately, the observer, together with the planet, travels around the Sun during the year, and if he makes two observations of the same star with an interval of several months, it turns out that he is considering it from different points of the earth's orbit - and this is already a decent basis . The direction of the star will change: it will shift slightly against the background of more distant stars. This displacement is called parallax, and the angle by which the star has shifted on the celestial sphere is called parallax. The annual parallax of a star is the angle at which the average radius of the earth's orbit was visible from it, perpendicular to the direction to the star.
The name of one of the basic units of distances in astronomy, the parsec, is associated with the concept of parallax. This is the distance to an imaginary star whose annual parallax would be exactly 1"". The annual parallax of any star is related to its distance by a simple formula:
where r is the distance in parsecs, P is the annual parallax in seconds.
Now the parallax method has determined the distances to many thousands of stars.
Now, knowing the distance to the star, you can determine its luminosity - the amount of energy it actually emits. It is characterized by absolute magnitude.
Absolute magnitude (M) is the magnitude that a star would have at a distance of 10 parsecs (32.6 light years) from an observer. Knowing the apparent stellar magnitude and the distance to the star, you can find its absolute stellar magnitude:
M=m + 5 - 5 * log(r)
Proxima Centauri, the closest star to the Sun, is a tiny, dim red dwarf with an apparent magnitude of m=-11.3 and an absolute magnitude of M=+15.7. Despite its proximity to the Earth, such a star can only be seen with a powerful telescope. An even dimmer star No. 359 according to Wolf's catalog: m = 13.5; M=16.6. Our Sun shines brighter than Wolf 359 by 50,000 times. The star dGolden Fish (in the southern hemisphere) has only 8th apparent magnitude and is not visible to the naked eye, but its absolute magnitude is M=-10.6; it is a million times brighter than the sun. If it were at the same distance from us as Proxima Centauri, it would shine brighter than the Moon on a full moon.
For the Sun M=4.9. At a distance of 10 parsecs, the sun will be visible as a faint star, hardly visible to the naked eye.
Luminosity of stars
The luminosity of stars (L) is more often expressed in units of the luminosity of the Sun (4x erg/s). Stars differ in luminosity over a very wide range. Most of the stars are "dwarfs", their luminosity is sometimes negligible even in comparison with the Sun. Luminosity characteristic is the "absolute value" of the star. There is also the concept of "apparent stellar magnitude", which depends on the luminosity of the star, color and distance to it. In most cases, "absolute magnitude" is used to realistically estimate the size of stars, no matter how far away they are. To find out the true value, you just need to refer the stars to some conditional distance (let's say 10 PCs). High luminosity stars have negative values. For example, the apparent magnitude of the sun is -26.8. At a distance of 10 PCs, this value will already be +5 (the faintest stars visible naked eye have a value of +6).
Radius of stars
star radius. Knowing the effective temperature T ef and luminosity L, we can calculate the radius R of the star using the formula:
based on the Stefan-Boltzmann radiation law (s is Stefan's constant). The radii of a star with large angular dimensions can be measured directly with stellar interferometers. For eclipsing binaries, the largest diameters of the components can be calculated, expressed as fractions of the semi-major axis of their relative orbit.
Surface temperature
surface temperature. The distribution of energy in the spectra of hot bodies is not the same; depending on the temperature, the maximum radiation falls on different lengths waves, the color of the total radiation changes. The study of these effects in a star, the study of the distribution of energy in stellar spectra, and the measurements of color indices make it possible to determine their temperatures. The temperatures of stars are also determined by relative intensities some lines in their spectrum, which makes it possible to establish the spectral type of stars. The spectral classes of stars depend on temperature and, with decreasing temperature, are denoted by the letters: O, B, A, F, G, K, M. In addition, a side row of carbon stars C branches off from class G, and a side branch S from class K. From O-class emit hotter stars. Knowing the mechanism for the formation of lines in the spectra, the temperature can be calculated from the spectral type if the acceleration of gravity on the surface of the star is known, which is related to the average density of its photosphere, and, consequently, to the size of the star (the density can be estimated from the subtle features of the spectra). The dependence of the spectral class or color index on the effective temperature of a star is called the effective temperature scale. Knowing the temperature, it is possible to theoretically calculate what fraction of the star's radiation falls on the invisible regions of the spectrum - ultraviolet and infrared. The absolute stellar magnitude and a correction that takes into account radiation in the ultraviolet and infrared parts of the spectrum make it possible to find the total luminosity of a star.
Radiation emitted from a small section of a luminous surface of a unit area. It is equal to the ratio of the luminous flux emanating from the small surface area under consideration to the area of this area:
,where dΦ is the luminous flux emitted by a surface area d S. Luminosity is measured in lm/m². 1 lm / m² is the luminosity of a surface of 1 m 2, emitting a luminous flux equal to 1 lm.
Luminosity does not depend on the distance to the object, only the apparent stellar magnitude depends on it. Luminosity is one of the most important stellar characteristics that allows you to compare different types stars on the diagrams "spectrum - luminosity", "mass - luminosity". The luminosity of a star can be calculated using the formula:
where R is the radius of the star, T- its surface temperature, σ - Stefan-Boltzmann coefficient.
Collider luminosity
In experimental particle physics luminosity called the parameter of the accelerator or collider characterizing the intensity of the collision of particles of two colliding beams, or beam particles with particles of a fixed target. The luminosity L is measured in cm −2 s −1 . Multiplying the reaction cross section by the luminosity yields the average frequency of this process at the given collider.
Notes
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See what "Luminance" is in other dictionaries:
LUMINOSITY- at a point on the surface. one of the luminous quantities, the ratio of the luminous flux emanating from a surface element to the area of this element. The unit C. (SI) is lumens per square meter (lm/m2). A similar value in the system of energetic. quantities called ... ... Physical Encyclopedia
luminosity- The ratio of the luminous flux emitted by a luminous surface to the area of \u200b\u200bthis surface [Terminological dictionary for construction in 12 languages \u200b\u200b(VNIIIS Gosstroy of the USSR)] luminosity (Mν) A physical quantity determined by the ratio ... ... Technical Translator's Handbook
LUMINOSITY- LUMINOSITY, the absolute brightness of a STAR is the amount of energy emitted by its surface per second. It is expressed in watts (joules per second) or units of measure for the brightness of the sun. Bolometric luminosity measures total power starlight on ... ... Scientific and technical encyclopedic dictionary
LUMINOSITY- LUMINOSITY, 1) in astronomy, the total amount of energy emitted by a space object per unit time. Sometimes one speaks of luminosity in a certain range of wavelengths, such as radio luminosity. Usually measured in erg / s, W, or in units of ... ... Modern Encyclopedia
LUMINOSITY- star radiation power. Usually expressed in units equal to the luminosity of the Sun L? \u003d 3.86? 1026 W ...
LUMINOSITY- the value of the total luminous flux emitted by a unit surface of the light source. Measured in lm/m² (in SI) … Big Encyclopedic Dictionary
LUMINOSITY- (lightness) physical. a value equal to the ratio of the light (cm.) F emitted by a luminous surface to the area S of this surface: R \u003d F / S In SI, it is expressed in (cm.) square meter(lm/m2) … Great Polytechnic Encyclopedia
Luminosity- I Luminosity at a point on a surface, the ratio of the luminous flux (See Luminous Flux) emanating from a small surface element that contains a given point to the area of this element. One of the light quantities (See Light quantities). ... ... Great Soviet Encyclopedia
luminosity- and; well. Astron. Luminous flux emitted by a unit surface of a light source. S. stars (the ratio of the luminous intensity of a star to the luminous intensity of the Sun). C. night sky (glow of atoms and molecules of air in the high layers of the atmosphere). * * * luminosity I… … encyclopedic Dictionary
Luminosity- in astronomy, the total energy emitted by a source per unit of time (in absolute units or in units of solar luminosity; solar luminosity = 3.86 1033 erg/s). Sometimes they do not talk about complete S., but about S. in a certain range of wavelengths. For example, in… … Astronomical dictionary
Imagine that somewhere in the sea in the darkness of the night, a light flickers quietly. If an experienced sailor does not explain to you what it is, you often will not know whether it is a flashlight on the bow of a passing boat in front of you, or a powerful searchlight from a distant lighthouse.
In the same position in dark night We are also looking at the twinkling stars. Their apparent brilliance also depends on their true power of light, called luminosity, and from their distance to us. Only knowing the distance to a star allows us to calculate its luminosity compared to the Sun. Thus, for example, the luminosity of a star ten times less luminous in reality than the Sun is expressed by the number 0.1.
The true strength of the light of a star can be expressed in another way, by calculating what magnitude it would seem to us if it were at a standard distance of 32.6 light years from us, that is, at such that light, rushing at a speed of 300,000 km /sec, would pass it during this time.
Accepting such a standard distance proved to be convenient for various calculations. The brightness of a star, like any light source, varies inversely with the square of the distance from it. This law allows you to calculate the absolute magnitudes or luminosities of stars, knowing the distance to them.
When the distances to the stars became known, we were able to calculate their luminosities, that is, we could, as it were, line them up in one line and compare them with each other under the same conditions. It must be confessed that the results were astonishing, since it had previously been assumed that all stars were "similar to our Sun." The luminosities of the stars turned out to be amazingly diverse, and they cannot be compared in our line with any line of pioneers.
Let us give only extreme examples of luminosity in the world of stars.
The weakest known for a long time was a star, which is 50 thousand times weaker than the Sun, and its absolute luminosity value: +16.6. However, even fainter stars were subsequently discovered, the luminosity of which, compared to the sun, is millions of times less!
Dimensions in space are deceptive: Deneb from Earth shines brighter than Antares, but the Pistol is not visible at all. However, to an observer from our planet, both Deneb and Antares seem to be just insignificant points compared to the Sun. How wrong this is can be judged by a simple fact: A gun releases as much light in a second as the Sun does in a year!
On the other side of the line of stars stands "S" Dorado, visible only in the countries of the Southern Hemisphere of the Earth as an asterisk (that is, not even visible without a telescope!). In fact, it is 400 thousand times brighter than the Sun, and its absolute luminosity value is -8.9.
Absolute the magnitude of the luminosity of our Sun is +5. Not so much! From a distance of 32.6 light years, we would not have seen it well without binoculars.
If the brightness of an ordinary candle is taken to be the brightness of the Sun, then in comparison with it, the “S” of Doradus will be a powerful searchlight, and the faintest star is fainter than the most miserable firefly.
So, the stars are distant suns, but their light intensity can be completely different from that of our luminary. Figuratively speaking, it would be necessary to change our Sun for another one with caution. From the light of one we would be blind, by the light of the other we would wander as in twilight.
Magnitudes
Since the eyes are the first instrument of measurement, we must know simple rules, to which our estimates of the brightness of light sources obey. Our estimate of the brightness difference is relative rather than absolute. Comparing two faint stars, we see that they are noticeably different from each other, but for two bright stars the same difference in brightness remains unnoticed by us, since it is negligible compared to the total amount of light emitted. In other words, our eyes evaluate relative, but not absolute gloss difference.
Hipparchus first divided the stars visible to the naked eye into six classes, according to their brightness. Later, this rule was somewhat improved without changing the system itself. The magnitude classes were distributed so that a 1st magnitude star (middle of 20) gave off a hundred times more light than a 6th magnitude star, which is at the limit of visibility for most people.
A difference of one magnitude equals the square of 2.512. A difference of two magnitudes corresponds to 6.31 (2.512 squared), three magnitudes to 15.85 (2.512 to the third power), four magnitudes to 39.82 (2.512 to the fourth power), and five magnitudes to 100 (2.512 to the power of fifth degree).
A 6th magnitude star gives us a hundred times less light than a 1st magnitude star, and an 11th magnitude star ten thousand times less. If we take a star of the 21st magnitude, then its brightness will be less than 100,000,000 times.
As it is already clear - the absolute and relative driving value,
things are completely incomparable. To a "relative" observer from our planet, Deneb in the constellation Cygnus looks something like this. And in fact, the entire orbit of the Earth would barely be enough to completely contain the circumference of this star.
To correctly classify stars (and they all differ from each other), care must be taken to maintain a brightness ratio of 2.512 along the entire interval between neighboring stellar magnitudes. It is impossible to do such work with a simple eye; special tools are needed, according to the type photometers Pickering, who use the Polar Star or even an "average" artificial star as a standard.
Also, for the convenience of measurements, it is necessary to weaken the light of very bright stars; this can be achieved either with a polarizing device, or with the help of photometric wedge.
Purely visual methods, even with the help of large telescopes, cannot extend our scale of stellar magnitudes to faint stars. In addition, visual methods of measurement should (and can) be made only directly at the telescope. Therefore, a purely visual classification has already been abandoned in our time, and the photoanalysis method is used.
How can you compare the amount of light received by a photographic plate from two stars of different brightness? To make them appear the same, it is necessary to attenuate the light from the brighter star by a known amount. The easiest way to do this is to put the aperture in front of the telescope lens. The amount of light entering a telescope varies with the area of the lens, so that any star's light attenuation can be accurately measured.
Let's choose some star as a standard one and photograph it with a full aperture of the telescope. Then we determine which aperture should be used at a given exposure so that when shooting a brighter star, we get the same image as in the first case. The ratio of the areas of the reduced and full holes gives the ratio of the brightness of the two objects.
This method of measurement gives an error of only 0.1 magnitude for any of the stars in the range from 1st to 18th magnitude. The magnitudes obtained in this way are called photovisual.
Stars throw into outer space a huge amount, almost completely represented by different types rays. The total energy of the radiation of the star, emitted over a period of time - this is the luminosity of the star. The luminosity index is very important for the study of luminaries, since it depends on all the characteristics of the star.
The first thing to note when talking about the luminosity of a star is that it is easy to confuse it with other parameters of the star. But in fact, everything is very simple - you just need to know what each characteristic is responsible for.
The luminosity of a star (L) reflects primarily the amount of energy emitted by the star - and therefore is measured in watts, like any other quantitative characteristic of energy. This is an objective value: it does not change when the observer moves. This parameter is 3.82 × 10 26 W. The brightness indicator of our star is often used to measure the luminosity of other stars, which is much more convenient for comparison - then it is marked as L ☉, (☉ is the graphic symbol of the Sun.)
Obviously, the most informative and universal characteristic among the above is luminosity. Since this parameter displays the intensity of the star's radiation in the most detailed way, it can be used to find out many characteristics of the star - from size and mass to intensity.
Luminosity from A to Z
It doesn't take long to find a source of radiation in a star. All the energy that can leave the luminary is created in the process thermonuclear reactions synthesis in . Hydrogen atoms, merging under the pressure of gravity into helium, release a huge amount of energy. And in the stars, not only hydrogen, but also helium “burns” more massively - sometimes even more massive elements, up to iron. Energy is then obtained many times more.
The amount of energy released during a nuclear reaction directly depends on - the larger it is, the more gravity compresses the core of the star, and the more hydrogen is simultaneously converted into helium. But not only nuclear energy determines the luminosity of a star - after all, it must also be radiated outward.
This is where radiation area comes into play. Its influence in the process of energy transfer is very great, which is easily verified even in everyday life. An incandescent lamp, the filament of which heats up to 2800 ° C, will not significantly change the temperature in the room in 8 hours of operation - and an ordinary battery with a temperature of 50–80 ° C will be able to warm the room to a noticeable stuffiness. The difference in efficiency is caused by differences in the amount of surface that radiates energy.
The ratio of the area of the core of a star to its core is often commensurate with the proportions of a light bulb filament and a battery - the diameter of the core can be as little as one ten-thousandth of the total diameter of the star. Thus, the luminosity of a star is seriously affected by the area of its radiating surface - that is, the surface of the star itself. The temperature here is not so significant. The incandescence of the star's surface is 40% less than the temperature of the Sun's photosphere - but due to its large size, its luminosity exceeds the solar one by 150 times.
It turns out that in calculating the luminosity of a star, the role of size is more important than the energy of the nucleus? Not really. Blue giants with high luminosity and temperature have similar luminosities to red supergiants, which are much bigger sizes. In addition, the most massive and one of the hottest stars, has the highest brightness of all known stars. Before the discovery of a new record holder, this puts an end to the discussion about the most important parameter for luminosity.
Use of luminosity in astronomy
Thus, luminosity fairly accurately reflects both the energy of a star and its surface area - which is why it is involved in many classification charts used by astronomers to compare stars. Among them, it is worth highlighting the diagram
