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 - 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 designate fractional numbers. The brightest stars, as well as planets, have zero or even negative value. 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 stars on 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 star of the second magnitude and 2.52 = 6.25 times brighter than a star of the third magnitude.
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 will turn out that he is viewing it from different points 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 parallactic, and the angle by which the star has shifted by celestial sphere, - parallax. The annual parallax of a star is the angle at which it was visible from it. average radius Earth's orbit, perpendicular to the direction of the star.
The name of one of the basic units distances in astronomy - parsec. 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 in 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; she 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 use " absolute value"to really estimate the size of the stars, no matter how far away they are. To find out the true size, you just need to refer the stars to some conventional distance (let's say 10PCs). 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 values can be calculated largest diameters components, expressed in 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 from the relative intensities of certain lines in their spectrum, which makes it possible to establish spectral class 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 associated with medium density its photosphere, and, consequently, the size of the star (the density can be estimated from the subtle features of the spectra). The dependence of the spectral type or color index on the effective temperature of a star is called the scale effective temperatures. 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.
star luminosity Luminosity stars, the luminous intensity of a star, that is, the magnitude of the light flux emitted by a star, contained in a unit solid angle. The term "luminosity of a star" does not correspond to the term "luminosity" of general photometry. The solar radiation of a star can refer both to some region of the spectrum of a star (the visual solar radiation of a star, the photographic solar radiation of a star, and so on) or to its total radiation (the bolometric solar radiation of a star). The S. of a star is usually expressed in units of the luminosity of the Sun, equal to 3 1027 international candles, or 3.8 1033 erg / sec. Luminosities individual stars differ greatly from each other: there are stars whose bolometric luminosity reaches half a million in units of the luminosity of the Sun (supergiant stars of the spectral class O), as well as stars with a bolometric luminosity that is hundreds of thousands of times less than solar. It is assumed that there are stars with even lower luminosity. Along with masses, radii and surface temperatures stars, luminosities are the most important characteristics stars. The connection between these stellar characteristics is considered in theoretical astrophysics. S. star L is related to the absolute magnitude M addiction:
M = - 2.5 log L + 4.77.
See also Art. Stars or T. with her.
Big soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what "Star Luminosity" is in other dictionaries:
AT general physics, luminosity is the flux density of light energy in this direction. AT experimental physics elementary particles luminosity is the parameter of an accelerator or collider that characterizes the intensity of the collision of colliding beams ... Wikipedia
A quantity measured as the ratio of the total energy that a star emits to the time of emission. The unit of C. star is in SI watts. The S. of the Sun, equal to 3.86 1026 W, is used as a unit for the luminosity of other stars ... Astronomical dictionary
Luminosity is a term used to refer to certain physical quantities. Contents 1 Photometric luminosity 2 Luminosity of a celestial body ... Wikipedia
Star radiation power. Usually expressed in units equal to the luminosity Sun L? \u003d 3.86? 1026 W ... Big Encyclopedic Dictionary
hot luminous celestial bodies similar to the sun. Stars vary in size, temperature, and brightness. In many respects, the Sun is a typical star, although it seems much brighter and larger than all other stars, since it is located much closer to ... ... Collier Encyclopedia
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 given point, to the area of this element. One of the light quantities (See. Light quantities).… … Great Soviet Encyclopedia
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 the total power of a star's light per... ... Scientific and technical encyclopedic dictionary
LUMINOSITY of a star, radiation power. Usually expressed in units equal to the luminosity of the Sun L¤ = 3.86×1026 W ... encyclopedic Dictionary
Stars large sizes and high luminosities. The radius of the giant reaches 1000 radii of the Sun, and the luminosity is 1000 times greater than the luminosity of the Sun. Giants have low average densities due to extended rarefied shells. Some… … Astronomical dictionary
Stars, radiation power. Usually expressed in units of solar luminosity 1.0 = 3.86 * 1026 W ... Natural science. encyclopedic Dictionary
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, which makes it possible 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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- Cooperation
- composite material
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 this surface [ Terminological dictionary on construction in 12 languages (VNIIIS Gosstroy of the USSR)] luminosity (Mν) 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 the total power of a star's light per... ... Scientific and technical encyclopedic dictionary
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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
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luminosity- and; and. 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
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Stars. Luminosity, spectrum and classification.
Some stars shine more powerfully, others - weaker. The power of a star's radiation is called its luminosity. Luminosity is the total energy emitted by a star in 1 second. The luminosity of a star characterizes the flow of energy radiated by the star in all directions, and has the dimension of power J/s or W. Luminosity is determined if the apparent magnitude and distance to the star are known. If astronomy has quite reliable instrumental methods for determining the apparent magnitude, then it is not so easy to determine the distance to the stars. The absolute magnitude of the Sun in the entire range of radiation (bolometric magnitude) M = 4.72, its luminosity L = 3.86∙10 26 W. Knowing the absolute magnitude, you can find the luminosity: lg L / L = 0.4 (M - M).
| Star | Luminosity |
| Sirius | 22L |
| Canopus | 4700L |
| Arcturus | 107 L |
| Vega | 50L |
The luminosities of other stars are determined in relative units compared to the luminosity of the sun. Stars are known that radiate tens of thousands of times less than the Sun. And the star S Doradus, visible only in countries southern hemisphere Earth as an asterisk of the 8th magnitude (not visible to the naked eye!), A million times brighter than the Sun, its absolute magnitude M = -10.6. Stars can differ in luminosity by a billion times. Among the stars of very high luminosity, giants and supergiants are distinguished. Most giants have a temperature of 3,000–4,000 K, which is why they are called red giants.
Aldebaran is a red giant in the constellation Taurus.
Alpha Orion - Betelgeuse. Supergiants, such as Betelgeuse, are the most powerful sources of light. Stars with low luminosity are called dwarfs.
A small dot next to Sirius is his satellite, white dwarf Sirius B. The spectra of stars are their passports with a description of all stellar features. The stars are made up of the same chemical elements, which are known on Earth, but in percentage they are dominated by light elements: hydrogen and helium. From the spectrum of a star, you can find out its luminosity, distance to the star, temperature, size, chemical composition its atmosphere, the speed of rotation around the axis, the features of movement around common center gravity. The spectral apparatus mounted on a telescope decomposes the light of a star into wavelengths into a spectrum strip. From the spectrum, you can find out how much energy comes from a star to various lengths waves and estimate its temperature very accurately. The color and spectrum of stars is related to their temperature. In cold stars with a photosphere temperature of 3000 K, radiation in the red region of the spectrum predominates. The spectra of such stars contain many lines of metals and molecules. In hot blue stars with temperatures over 10,000–15,000 K most of atoms is ionized. Fully ionized atoms do not give spectral lines, so there are few lines in the spectra of such stars.
According to their spectra, stars are divided into spectral classes:
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Spectra of various stars. A characteristic feature of stellar spectra is also the presence of huge amount absorption lines belonging various elements. A fine analysis of these lines made it possible to obtain especially valuable information on the nature of the outer layers of stars.
The chemical composition of the outer layers of stars, from where their radiation directly comes to us, is characterized by the complete predominance of hydrogen. In second place is helium, and the number of other elements is quite small. Approximately for every ten thousand hydrogen atoms, there are a thousand helium atoms, about 10 oxygen atoms, slightly less carbon and nitrogen, and only one iron atom. The impurities of other elements are absolutely negligible. It is no exaggeration to say that stars are composed of hydrogen and helium with a small admixture of heavier elements. A good indicator of the temperature of a star's outer layers is its color. Hot stars of spectral types O and B are blue; stars similar to our Sun (whose spectral type is G2) appear yellow, while stars of spectral classes K and M are red. In astrophysics there is a carefully developed and quite objective system of colors. It is based on a comparison of the observed magnitudes obtained through various strictly standardized light filters. Quantitatively, the color of stars is characterized by the difference between two values obtained through two filters, one of which transmits predominantly blue rays (“B”), and the other has a spectral sensitivity curve similar to human eye("V"). The technique for measuring the color of stars is so high that, according to the measured value B-V one can determine the spectral class of a star up to a subclass. For faint stars, color analysis is the only possibility for their spectral classification.
Harvard spectral classification based on the presence or absence, as well as the relative intensity of certain spectral lines.
In addition to the main spectral types listed in the table for relatively cold stars, there are also N and R classes (absorption bands of carbon C2 molecules, cyanide CN and carbon monoxide CO), class S (bands of oxides of titanium TiO and zirconium ZrO), as well as for the coldest stars – class L (CrH band, lines of rubidium, cesium, potassium, and sodium). For objects of substellar type - "brown dwarfs", intermediate in mass between stars and planets, a special spectral class T (absorption bands of water, methane and molecular hydrogen) has recently been introduced. Spectral types O, B, A are often called hot or early, classes F and G - solar, and classes K and M - cold or late spectral types. For a finer definition of stellar spectra, the intervals between the listed classes are divided into 10 subclasses. For example, F5 is the spectrum midway between F0 and G0. The spectral class of the Sun is G2.
Ability to measure and compare gloss different stars led to the discovery new area in astronomy - colorimetry. Colorimetry is the measurement and study of the color of stars.
The perception of color is purely subjective, it depends on the reaction of the retina of the observer's eye. The color sensitivity of the human eye is limited approximately to the following area: from violet rays (4000 A) to red rays (7500 A). Stars radiate energy in all ranges electromagnetic spectrum, not only in the visible region. The colors of stars are determined by the ratio of the radiation intensities in two or more regions of the spectrum. Initially, the color of the stars was proposed to be measured using photographs. If a star is photographed on two photographic plates, one of which is sensitive to shorter, blue rays, and the second to longer, red rays, then blackening, that is, the apparent magnitude on different photographic plates, will be different. The difference between photographic magnitudes was called the color index CI (English color index).
CI = m(1) – m(2). Red stars have positive color indices, and blue and white stars- negative. With the development of photometric measurement technology and the advent of photomultipliers, it was agreed to use the U, B, V color system. The U, B, V system replaced the previous photographic and photovisual color determination system. The U color system measures stellar magnitudes in the ultraviolet region of the spectrum, the B color system - in the usual photographic region, which corresponds to blue rays, and the V color system - in the region of the color that prevails in the illumination of our planet, i.e. yellow color.
UBV system.
Index colors B-V allows you to compare the radiation intensities in blue and yellow rays, and the U-B color index in the ultraviolet and blue range of the spectrum. We agreed to consider that the B-V color index for an AO-class star zero. This corresponds to a flux of quanta with a wavelength of 5550 A. If the color index of the star main sequence negative, then this is a star of early spectral types with a surface temperature greater than 10,000 K. If the color index is positive, then this is a star of late spectral types with a surface temperature of less than 10,000 K. Thus, in colorimetry, a relationship is established between the B-V color index, spectral class, and photosphere temperature for main sequence stars. stars, for the rarest exception, are observed as point sources of radiation. This means that their angular dimensions are very small. Even in the most large telescopes you can't see the stars as "real" disks. Star even in the most large telescope cannot be allowed.
Methods for determining the size of stars:
- by observing the eclipse of a star by the Moon, one can determine the angular size, and, knowing the distance to the star, one can determine its true, linear dimensions;
- directly the size of the star can be measured on special device– optical interferometer;
- the dimensions of a star can be theoretically calculated from estimates of the total luminosity and temperature using the Stefan–Boltzmann law.
Comparative sizes of the Sun and dwarfs.
The sizes of stars differ significantly among themselves: there are dwarfs, giants and ordinary stars, which are the majority. Measurements showed that the size of white dwarfs is several thousand kilometers, and the size of red giants is comparable to the size of solar system. The mass of a star is perhaps its most important characteristic. Mass determines the whole life path stars. The mass can be estimated for stars in binary star systems if known semi-major axis orbits a and rotation period T. In this case, the masses are determined from Kepler's third law, which can be written as follows: here M1 and M2 are the masses of the system components, G is the gravitational constant. The equation gives the sum of the masses of the system components. If, in addition, the relation orbital speeds, then their masses can be determined separately. Unfortunately, only for a relatively small number of binary systems can the mass of each of the stars be determined in this way.
All other methods of estimating mass are indirect. In essence, astronomy did not have and does not currently have the method of direct and independent definition the mass of an isolated star. And this is a serious shortcoming of our science of the universe. If such a method existed, the progress of our knowledge would be much more rapid. For main sequence stars, it has been established that the more weight, the higher the luminosity of the star. This dependence is non-linear: for example, with a doubling of the mass, the luminosity increases by more than 10 times. The smallest stars in terms of mass are much more massive than any planet in the solar system. The masses of stars range from 0.1 solar masses to several tens of solar masses. Thus, the masses of the stars differ by only a few hundred times.
Comparisons of masses and luminosities for most stars revealed following dependency: luminosity is approximately proportional to the fourth power of mass.
The density of gas at the center of the Sun is a hundred times greater than the density of water. A star that weighs twice as much as the Sun radiates about 16 times more powerfully. Under the influence high temperature(millions of kelvins), the atoms of the nucleus are completely ionized, and the distances between them are reduced. The density of gas at the center of the Sun is a hundred times greater than the density of water. The temperature of the star also increases as it approaches the center. Stars of early spectral types O, B, A are also characterized by high rotation rates.
Equatorial stellar rotation velocities: spectrum v, km/s O5 400 A0 320 A5 250 F0 180
The highest observed velocities have been found in stars with emission lines in the spectrum and, of course, in neutron stars. Our Sun rotates at an equatorial speed of 2 km/s. Stars vary greatly in size, luminosity, and temperature.
Due to their huge surface area, the giants radiate immeasurably more energy than normal stars like the Sun, even though their surface temperatures are much cooler. The radius of the red supergiant Betelgeuse (cons. Orion) is many times greater than the radius of the Sun. On the contrary, the size of a normal red star, as a rule, does not exceed one tenth of the size of the Sun. In contrast to giants, they are called dwarfs. For example, two stars with the same spectral type M2, Betelgeuse and Lalande 21185, differ in luminosity by a factor of 600,000. The luminosity of Betelgeuse is 3000 times greater than the luminosity of the Sun, and Lalande 21185 is 200 times less. Stars are giants and dwarfs on different stages of its evolution, and the giant, having reached "old age", can turn into a white dwarf. Along with red giants and supergiants, there are white and blue supergiants: Regulus (α Leo), Rigel (β Orion).
Source of information: "Open Astronomy 2.5", LLC "FISICON"
