(denoted by m - from English. magnitude) - a dimensionless quantity characterizing the brightness of a celestial body (the amount of light coming from it) from the point of view of an earthly observer. The brighter an object, the smaller its apparent magnitude.
The word "apparent" in the name only means that the magnitude is observed from the Earth, and is used to distinguish it from the absolute magnitude. This name refers not only to visible light. The quantity that is perceived by the human eye (or other receiver with the same spectral sensitivity) is called visual.
The recognition of double stars, for which methods were applied, including those associated with the recognition of many stars in general, had a rather interesting role in eighteenth century astronomy. Galileo noted that if two stars are casually almost in the same direction as compared to the Earth, and if one is much farther away than the other, then the furthest can be a practically fixed reference point provided by Nature's bounty with which astronomers can control the apparent annual motions of the nearest star. These two stars would suffer refraction in the same way, and one of the disturbing effects would be bypassed; The same that we add was also true of aberration and nutation, which, of course, were unknown to Galileo.
magnitude denoted by a lowercase m as a superscript to a numeric value. For example, 2 m means the second magnitude.
Story
The concept of magnitude was introduced by the ancient Greek astronomer Hipparchus in the 2nd century BC. He distributed all the stars accessible to the naked eye into six magnitudes: he called the bright stars of the first magnitude, the naytmyanish - the sixth. For intermediate magnitudes, it was believed that, say, stars of the third magnitude, are as dimmer as the stars of the second magnitude, as they are brighter than the stars of the fourth. This method of measuring brilliance gained popularity thanks to the Almagest, the star catalog of Claudius Ptolemy.
Being a musician and composer, born in Germany, as a self-taught scientist, he did not know that the "true" astronomers they focused their efforts on the bodies of the solar system, using the stars, and not the background of the movements of planets and comets. On the other hand, Herschel is increasingly obsessed with "building heaven." With the help of a godly sister, Caroline, who in turn has become a famous comet hunter, builds ever larger illuminated telescopes with which to explore the far-reaching and easily bright objects that fill the universe.
This discovery was of great importance to professional scientists who considered Herschel a pretext for putting pressure on the king and granting him a pension; this allowed him to give up music to devote himself to astronomy, with the sole responsibility of living near Windsor Castle and being ready to illustrate heaven to the royal family when needed. One of Herschel's first publications as a professional astronomer was a list of 269 double stars that he noticed during his research.
Such a classification scale was used almost unchanged until the middle of the 19th century. The first who treated the stellar magnitude as a quantitative rather than a qualitative characteristic was Friedrich Argelander. It was he who began to confidently apply decimal fractions of stellar magnitudes.
1856 Norman Pogson formalized the magnitude scale, establishing that a first magnitude star is exactly 100 times brighter than a sixth magnitude star. Since, in accordance with the Weber-Fechner law, the change in illumination the same number of times perceived by the eye as a change by the same amount then a difference of one magnitude corresponds to a change in light intensity by a factor of ≈ 2.512. This is an irrational number that is called Pogson number.
He hoped that they might be useful in determining the annual parallax using Galileo's method. Unfortunately, Herschel, a self-born amateur scientist who was, did not know the important writing on stellar astronomy by Cambridge geologist John Michell, published in the Philosophical Transactions of the Royal Society of London here. Michel showed that the number of twin stars far exceeded the number that could be estimated on the basis of the hypothesis that their existence was due only to the accidental circumstance that the two stars seen from Earth were in the same direction.
So, the scale of stellar magnitudes is logarithmic: the difference in stellar magnitudes of two objects is determined by the equation:
, , are the stellar magnitudes of objects, , are the illuminations created by them.This formula makes it possible to determine only the difference in stellar magnitudes, but not the magnitudes themselves. In order to build an absolute scale with its help, it is necessary to set a zero point — illumination, which corresponds to zero magnitude (0 m). At first, Pogson used the North Star as a standard, assuming that it has exactly the second magnitude. After it became clear that Polaris was a variable star, the scale began to be tied to Vega (which was assigned a zero value), and then (when Vega was also suspected of variability), the zero point of the scale was redefined with the help of several other stars. However, for visual observations, Vega can serve as a standard of zero magnitude even further, since its magnitude in visible light is 0.03 m, which does not differ from zero by eye.
He concluded that most of the binary stars were binary stars, that is, groups of two physically connected stars, supposedly held together by gravity, which were then at the same distance from the Earth and could not be used for the purposes of application according to the method indicated by Galileo Michell, calculated that if a star with the same density of the Sun had a radius 500 times greater, its gravitational attraction would be sufficient to prevent light from escaping: "Every light emitted by a good body would be forced to return to it due to its gravity."
The modern magnitude scale is not limited to six magnitudes or just visible light. The magnitude of very bright objects is negative. For example, Sirius, the brightest star in the night sky, has an apparent magnitude of -1.47m. Modern technology also makes it possible to measure the brightness of the Moon and the Sun: the full Moon has an apparent magnitude of -12.6 m, and the Sun -26.8 m. The Hubble Orbital Telescope can observe stars up to 31.5 m in the visible range.
However, this star could show its presence due to the influence of the force of gravitational attraction on a possible companion. The idea received a great deal of publicity when Pierre-Simon de Laplace introduced a similar rating to his cinema dumonde exposition, although this speculative idea was abandoned by astronomers shortly thereafter, only to be resumed in the present day. Immediately after the turn of the century, Herschel took the time to reconsider the double star pair, following Michell's claim that they were pairs of physically related companions.
He noticed that changes in their relative position on several occasions indicated that they were indeed bound by attractive forces. Newton himself had difficulty clearing the field of what turned out to be the decisive proof that gravity was not universal: the "fixation" of stars. Newton did not think that the answer to the dilemma lay in the enormity of interstellar distances, which depends on the fact that the movements of the stars are so small that it would be difficult to observe even for centuries. Even though he had a better understanding of the scale of interstellar distance than any other contemporary, this may have been the terminology he adopted to prevent him from understanding the possibility of a hidden motion of a star.
Spectral dependence
The stellar magnitude depends on the spectral range in which the observation is carried out, since the luminous flux from any object in different ranges is different.
- Bolometric magnitude shows the total radiation power of the object, that is, the total flux in all spectral ranges. Bolometer is measured.
The most common photometric system, the UBV system, has 3 bands (spectral ranges in which measurements are made). Accordingly, there are:
The scientist in the Book of Nature might be grateful to know how Providence, at the time of Creation, built a universe of stars that was practically stable, and also how Providence would always intervene from time to time if the system, despite the symmetrical distribution of the stars, was in danger of destroying it. In the theorems mentioned, Newton tried to prove that the brightest stars were mostly distributed equally into the heavens, as required by his symmetrical universe. His geometric model is about distances, although the data in the star catalogs were expressed in terms of brightness and positions on the celestial sphere, that is, the direction in relation to the Earth.
- ultraviolet magnitude (U)- determined in the ultraviolet range;
- "Blue" magnitude (B) — is determined in the blue range;
- visual magnitude (V)- is determined in the visible range; the spectral response curve is chosen to better match human vision. The eye is most sensitive to yellow-green light with a wavelength of about 555 nm.
The difference (U-B or B-V) between the magnitudes of the same object in different bands shows its color and is called the color index. The higher the color index, the redder the object.
By playing on the relationship between distances and magnitudes traditionally used to rank stars by brightness, Newton was able to convince the number of stars of successive magnitudes was about what one would expect from a symmetrical universe. Newton did little to fundamentally challenge his idea of a symmetrical universe, which arose from the existence of the Milky Way, with its high concentration of stars. The one who put Newton's problem on Milky Way, was William Stackley, who was not an astronomer but a physicist, and also an eminent antiquarian antique.
There are other photometric systems, each of which has different bands and, accordingly, different quantities can be measured. For example, in the old photographic system, the following quantities were used:
- photovisual magnitude (m pv)- a measure of blackening the image of an object on a photographic plate with an orange light filter;
- photographic magnitude (m pg)- measured on a conventional photographic plate, which is sensitive to the blue and ultraviolet ranges of the spectrum.
Apparent stellar magnitudes of some objects
| An object | m |
|---|---|
| Sun | -26,73 |
| Full moon | -12,92 |
| Iridium flare (maximum) | -9,50 |
| Venus (maximum) | -4,89 |
| Venus (minimum) | -3,50 |
| Jupiter (maximum) | -2,94 |
| Mars (maximum) | -2,91 |
| Mercury (maximum) | -2,45 |
| Jupiter (minimum) | -1,61 |
| Sirius (the brightest star in the sky) | -1,47 |
| Canopus (2nd brightest star in the sky) | -0,72 |
| Saturn (maximum) | -0,49 |
| Alpha Centauri cumulative brightness A, B | -0,27 |
| Arcturus (3rd brightest star in the sky) | 0,05 |
| Alpha Centauri A (4th brightest star in the sky) | -0,01 |
| Vega (5th brightest star in the sky) | 0,03 |
| Saturn (minimum) | 1,47 |
| Mars (minimum) | 1,84 |
| SN 1987A - supernova 1987 in the Large Magellanic Cloud | 3,03 |
| Andromeda's nebula | 3,44 |
| Faint stars that are visible in metropolitan areas | 3 … + 4 |
| Ganymede is a moon of Jupiter, the largest moon in the solar system (maximum) | 4,38 |
| 4 Vesta (bright asteroid), at maximum | 5,14 |
| Uranus (maximum) | 5,32 |
| Triangulum Galaxy (M33), visible to the naked eye in clear skies | 5,72 |
| Mercury (minimum) | 5,75 |
| Uranus (minimum) | 5,95 |
| Naytyanish stars visible to the naked eye in countryside | 6,50 |
| Ceres (maximum) | 6,73 |
| NGC 3031 (M81), visible to the naked eye under perfect skies | 6,90 |
| Nightmanish stars visible to the naked eye in a perfect sky (Mauna Kea Observatory, Atacama Desert) | 7,72 |
| Neptune (maximum) | 7,78 |
| Neptune (minimum) | 8,01 |
| Titan is a moon of Saturn, the 2nd largest moon in the solar system (maximum) | 8,10 |
| Proxima Centauri | 11,10 |
| The brightest quasar | 12,60 |
| Pluto (maximum) | 13,65 |
| Makemake in opposition | 16,80 |
| Haumea in opposition | 17,27 |
| Eris in opposition | 18,70 |
| Faint stars seen in a 24" CCD image with a 30 minute exposure | 22 |
| The smallest object available on the 8-meter ground-based telescope | 27 |
| The smallest object available on the Hubble Space Telescope | 31,5 |
| The smallest object that will be available on the 42-meter ground-based telescope | 36 |
| The smallest object that will be available on the OWL orbiting telescope (launch is scheduled for 2020) | 38 |
Related Images
In fact, Stookey left the center of the argument under the influence of gravitational forces, pointing to another apparent effect of the stars, which is the light they send to us. a false coincidence from a mathematical point of view, trying to prove that the effect did not really occur, since distant stars would only transmit a negligible amount of light to the Earth. Two of Halley's writings were published in Philosophical Transactions, and so the symmetrical universe thesis, long espoused by Newton, became public dominance.
The erroneous nature of Halley's reasoning did not go unnoticed. Nearby stars contribute to the brightness of the night sky with the same amount of light as twin stars, the same is true for three, three, fourfold stars, and so on ad infinitum. Since the reasoning applies to stars at large distances, we are allowed to imagine the night sky as completely bright, to shining with the same intensity. sunlight. The fact that this doesn't actually happen, according to Hese, can be explained by the presence of interstellar shadowing.
Even people far from astronomy know that stars have different brilliance. The brightest stars are easily visible in the overexposed city sky, while the dimmest ones are barely visible under ideal conditions observations. To characterize the brightness of stars and other celestial bodies (for example, planets, meteors, the Sun and the Moon), scientists have developed a scale of stellar magnitudes.
A more significant figure was that of Thomas Wright of Durham, a self-taught humble origin that he earned from a life of making England long and wide, holding public conferences and advising the aristocracy on the care of his belongings. Now, if the stars were stationary, the gravitational collapse would soon cause them to fall into Paradise, thus reducing the Divine Universe to chaos, so each star moved and moved around the God Mansion in an Orbit located inside a hollow ball.
To illustrate her concept, Wright used an excellent explanatory drawing that shows a cross section of the universe. In order to arouse the interest of his listeners by showing their placement in such a universe, he retreated from the region immediately surrounding solar system, the way it actually appears on Earth. He imagined a small group of nearby stars as isolated bright patches, gathering many distant stars that were just visible to form the "luminous circle of light," the Milky Way.
concept "star magnitude" used by astronomers for over 2000 years. Probably the first to introduce it was the famous ancient Greek astronomer and mathematician Hipparchus in the 2nd century BC. Regularly observing the starry sky from the island of Rhodes in the Aegean Sea, Hipparchus once witnessed the appearance of a new bright star in the constellation Scorpio. Impressed by this event, the astronomer decided to compile a catalog of stars in order to quickly find new stars in the future, if any. As a result, the astronomer rewrote 1025 stars: he not only gave the coordinates for each star, but also divided them into 6 magnitudes.
However, after a few years, he realized the error contained in this explanation of the Milky Way. The cross section of the universe he designed was just one of many possible cross sections, while the Milky Way forms one circle in the sky. Eventually, he modified his previous model to overcome this difficulty; A new version had the most emphasis in his excellent volume, Wright admitted that there is a second way to explain the Milky Way. If the system of stars surrounding the Divine Center formed not a sphere, but a ring in the form of a flattened disk, then the stars located directly around the observer placed inside the disk would again take on the appearance of the Milky Way.
by the most bright Hipparchus appropriated the stars first stellar magnitude, and most dim barely visible to the eye, sixth. At the same time, the stars of the 2nd magnitude were considered as many times weaker than the stars of the 1st, as the stars of the 3rd magnitude were weaker than the stars of the 2nd, and so on: an arithmetic progression was obtained. In the catalog of Hipparchus, there were 15 stars of the first magnitude, 45 stars of the second, 208 of the third, 474 of the fourth, 217 of the fifth and 49 stars of the sixth magnitude (plus several nebulae).
However, this model provided no explanation as to why the disk was on one plane and not the other. Wright's actual influence is difficult to ascertain. This would probably have been minimal had the book collection not appeared in a periodical in Hamburg the following year and been read by the young philosopher Immanuel Kant. Despite numerous illustrations of the original theory, Wright's ideas were barely understandable, so the simple illustrative collection was easy to understand. In addition, Wright, extravagantly developing his first assumptions, presented the Divine Center of the star system containing the Sun as simply one of innumerable divine centers, each of which Kant did not understand, who, without foundation, suggested that the Wright Universe contained a single Divine Center, which, according to him, was too far from our star system to have any bearing on the Milky Way's path explanations.
Why Hipparchus called the characteristic of the brightness of stars magnitude?
In ancient times, people believed that the stars were located in the celestial sphere at the same distance from the Earth, so the difference in the brightness of the stars was explained by the difference in their real sizes or size.Hence the stars of the first magnitude must have been much larger than the stars of the sixth magnitude.
Thus, there was no reason why a flattened disk should have an empty central region, according to Kant, it can be argued that the disk runs unhindered from the outer edge to the opposite outer edge. Certainly, Kant believed that he was offered two alternative models of our star system: one spherical and the other disk. He also believed that there were other similar systems in the universe, and the French Pierre-Louis Moreau de Maupertuis had already noticed how some of them had an elliptical layout.
In general, a circular disk will appear elliptical, and a sphere will appear circular in whatever direction it observed. Therefore, it was assumed that the systems observed by Maupertuis were in the form of a disk, not a sphere; because this Kant rejected Wright's spherical model of our star system and accepted the circular disk model. Thus we arrived at the first basically correct model of our Galaxy. The same problems were considered speculatively by the eclectic Alsatian scientist Johann Heinrich Lambert, a staunch supporter of the stability of the clocks of the Newtonian universe, in which cyclic movements were constantly repeated.
According to the scale introduced by Hipparchus, such stars as Deneb or Capella had the first magnitude (abbreviated as 1 m), and these were the largest, "important" stars. bucket stars Ursa Major had an average of 2 m, these were already "smaller" stars. Over time, astronomers realized that the stellar magnitude does not determine the real size of the star, but only its brilliance, that is the illumination it creates on earth, however, continued to use the Hipparchus scale.
It should be remembered that the scale of stellar magnitudes is the opposite: the brighter the star, the smaller its magnitude. Conversely, the dimmer a star is, the greater its magnitude.By the middle of the XIX century, the development of science required to determine the brightness of the stars more accurately. In particular, it turned out that human vision is arranged in a special way: when the illumination changes in geometric progression it conveys sensations to us in an arithmetic progression. It turned out that not 6 stars of the 6th magnitude will create the same illumination as the star of the 1st (as previously assumed), but a whole hundred!
In 1856, the English astronomer Norman Pogson proposed to build a scale of stellar magnitudes, taking into account the psychophysical law of vision. According to Pogson, a 1st magnitude star, by definition, created an illumination exactly 100 times greater than a 6m star. Thus, it turns out that the modern magnitude scale is logarithmic: a 1st magnitude star is about 2.512 times brighter than a 2nd magnitude star, and that, in turn, is 2.512 times brighter than a 3rd magnitude star, and so on.
Magnitude is a dimensionless characteristic of the brilliance of a heavenly body. This image shows the famous double cluster in the constellation Perseus. The brightest stars in the photo have a magnitude of 6, the dimmest - about the 17th. According to the Pogson formula brightest stars in the photo 25,000 times brighter than barely noticeable. © New Forest Observatory
But why report? What is taken as a zero point?
As you know, astronomy is an exact science, and therefore any physical characteristic must be measured in some quantities. So, force is measured in newtons, energy - in joules. In this sense, the stellar magnitude is a dimensionless characteristic of the brilliance of celestial bodies. Pogson proposed to consider the brightness of the Polar Star equal to exactly 2 m (just like Celsius took the freezing point of water as 0 °), and determine the magnitudes of the remaining stars, starting from it. But later it turned out that the brightness of the North Star is not constant, and then Vega was already taken as a standard. Today, 0 m is taken as a well-defined illumination equal to the energy value E=2,48*10^-8 W/m².
Actually, exactly illumination and are determined by astronomers during observations, and only then it is specially translated into stellar magnitudes.
They do this not only because “it’s more familiar,” but also because the magnitude turned out to be a very convenient concept. Measuring illumination in watts per square meter is extremely cumbersome: for the Sun, the value is large, and for faint telescopic stars, it is very small. At the same time, it is much easier to operate with stellar magnitudes (precisely due to the fact that this is a logarithmic scale). Thus, the brightness of the Sun is -26.73 m, and the brightness of the faintest objects that can be photographed using the Hubble telescope is approximately 31.50 m. As you can see, the difference is only 58 "steps".
In the beginning, magnitude was used as an indication of the brightness of stars that were observed optically (i.e., visually or photographically). Later, the scale was extended to the ultraviolet and infrared radiation ranges. It is clear that stars radiate unevenly at different wavelengths, so the stellar magnitude of a heavenly body depends on the spectral sensitivity of the radiation receiver.
visual magnitude mv corresponds to the spectral sensitivity of the human eye (the maximum falls on the wavelength lambda = 555 μm).
Photovisual magnitude V(or yellow) practically coincides with the visual one, and at present it is in the scale of photovisual magnitudes that the brilliance of stars and other celestial bodies is indicated in catalogs intended for astronomy lovers ..
photographic magnitude B(or blue) is determined by measuring the brightness of a star on a photographic plate sensitive to blue rays, or using a photomultiplier with a blue filter.
Finally, bolometric magnitude mbol corresponds to the total radiation power of the star in all ranges of the spectrum. For example, the bolometric stellar magnitude of the Sun is only slightly less than the visual magnitude, since almost all of the star's radiation is in the visible range. On the other hand, the bolometric sound led. red dwarfs are much smaller than their visual stars. magnitude, since most of the radiation energy is in the infrared range. The same situation is observed with hot stars of spectral classes O and B, which emit mainly in the ultraviolet.
Scale of stellar magnitudes. Picture: Big Universe
Until now, speaking of magnitude, we meant apparent magnitude , i.e., the one that is recorded directly when observing a celestial body. Apparent stellar magnitude means "observed", "apparent" and does not say anything about what real luminosity of a celestial body. For example, Venus in the sky looks much brighter than any star; its maximum brightness reaches -4.67 m. However, this does not mean that the planet "emits" more light than the stars; the great brilliance of Venus is due to its proximity to the Earth.
To compare the real fluxes of light energy coming from celestial bodies, astronomers conventionally place them at a standard distance of 10 parsecs from the Earth. Absolute magnitude (M) shows what apparent magnitude would a celestial body have if the distance to it was 10 parsecs.
Apparent stellar magnitudes of some celestial bodies
Sun: -26,73Moon (on a full moon): -12,74
Venus (at maximum brightness): -4,67
Jupiter (at maximum brightness): -2,91
Sirius: -1,44
Vega: 0,03
The faintest stars visible to the naked eye are: about 6.0
The sun from a distance of 100 light years: 7,30
Proxima Centauri: 11,05
The brightest quasar 12,9
The faintest objects photographed by the Hubble telescope: 31,5
