Cosmic scale. Universe scale
One of the authors of this article has worked quite a bit, for example, on the solar corona and the Galaxy. And they always seemed to him to be irregularly shaped spheroidal bodies of approximately the same size - something around 10 cm... Why 10 cm? This image arose subconsciously, simply because too often, while thinking about one or another issue of solar or galactic physics, the author drew the outlines of the objects of his thoughts in an ordinary notebook (in a box). I drew, trying to adhere to the scale of the phenomena. On one very interesting question, for example, it was possible to draw an interesting analogy between the solar corona and the Galaxy (or rather, the so-called “galactic corona”). Of course, the author knew very well, so to speak, “intellectually,” that the dimensions of the galactic corona are hundreds of billions of times larger than the dimensions of the solar corona. But he calmly forgot about it. And if in a number of cases the large dimensions of the galactic corona acquired some fundamental significance (this also happened), this was taken into account formally and mathematically. And still, visually, both “crowns” seemed equally small...
If the author, in the process of this work, indulged philosophical reflections about the enormity of the size of the Galaxy, about the unimaginable rarefaction of the gas that makes up the galactic corona, about the insignificance of our little planet and our own existence, and about other other equally valid subjects, work on the problems of the solar and galactic coronas would stop automatically...
Let the reader forgive me this “lyrical digression”. I have no doubt that other astronomers had similar thoughts as they worked through their problems. It seems to me that sometimes it is useful to become more familiar with the “kitchen” of scientific work...
Until relatively recently, the globe seemed huge to people. It took the brave companions of Magellan more than three years to accomplish the first trip around the world. A little over 100 years have passed since the resourceful hero fantasy novel Jules Verne made, using the latest technological advances of that time, a trip around the world in 80 days. And only a little less than 50 years have passed since those memorable days for all mankind, when the first Soviet cosmonaut Gagarin flew around on the legendary spaceship"Vostok" globe in 89 minutes. And people’s thoughts involuntarily turned to the vast expanses of space, in which the small planet Earth was lost...
1 parsec (pc) is equal to 3.26 light years. A parsec is defined as the distance from which the radius of the Earth's orbit is visible at an angle of 1 second. arcs. This is a very small angle. Suffice it to say that from this angle a one-kopeck coin is visible from a distance of 3 km.
None of the stars - the closest neighbors of the Solar System - are closer to us than 1 pc. For example, the mentioned Proxima Centauri is located at a distance of about 1.3 pc from us. On the scale in which we depicted the Solar System, this corresponds to 2 thousand km. All this well illustrates the great isolation of our Solar system from surrounding stellar systems; some of these systems may have many similarities with it.
But the stars surrounding the Sun and the Sun itself constitute only an insignificant part of the gigantic group of stars and nebulae, which is called the “Galaxy”. We see this cluster of stars on clear moonless nights as a stripe of the Milky Way crossing the sky. The galaxy has a rather complex structure. In the first, roughest approximation, we can assume that the stars and nebulae of which it consists fill a volume shaped like a highly compressed ellipsoid of revolution. Often in popular literature the shape of the Galaxy is compared to a biconvex lens. In reality, everything is much more complicated, and the picture drawn is too rough. In fact, it turns out that different types of stars concentrate in completely different ways towards the center of the Galaxy and towards its “equatorial plane”. For example, gaseous nebulae, as well as very hot massive stars, are strongly concentrated towards the equatorial plane of the Galaxy (in the sky this plane corresponds to a large circle passing through the central parts of the Milky Way). At the same time, they do not show a significant concentration towards the galactic center. On the other hand, some types of stars and star clusters (the so-called “globular clusters”) show almost no concentration towards the equatorial plane of the Galaxy, but are characterized by a huge concentration towards its center. Between these two extreme types of spatial distribution (which astronomers call "flat" and "spherical") are all the intermediate cases. However, it turns out that the bulk of the stars in the Galaxy are located in a giant disk, the diameter of which is about 100 thousand light years and the thickness is about 1500 light years. This disk contains slightly more than 150 billion stars of the most various types. Our Sun is one of these stars, located on the periphery of the Galaxy close to its equatorial plane (more precisely, “only” at a distance of about 30 light years - a value quite small compared to the thickness of the stellar disk).
The distance from the Sun to the core of the Galaxy (or its center) is about 30 thousand light years. Stellar density in the Galaxy is very uneven. It is highest in the region of the galactic core, where, according to the latest data, it reaches 2 thousand stars per cubic parsec, which is almost 20 thousand times more than the average stellar density in the vicinity of the Sun. In addition, stars tend to form distinct groups or clusters. A good example of such a cluster is the Pleiades, which are visible in our winter sky.
The Galaxy also contains structural details on a much larger scale. Research has proven that nebulae, as well as hot massive stars, are distributed along the branches of the spiral. The spiral structure is especially clearly visible in other star systems - galaxies (with a small letter, in contrast to our star system - Galaxies). Establishing the spiral structure of the Galaxy in which we ourselves find ourselves has proven extremely difficult.
Stars and nebulae within the Galaxy move in quite complex ways. First of all, they participate in the rotation of the Galaxy around an axis perpendicular to its equatorial plane. This rotation is not the same as that of a solid body: different parts of the Galaxy have different periods of rotation. Thus, the Sun and the stars surrounding it in a huge area several hundred light years in size complete a full revolution in about 200 million years. Since the Sun, together with its family of planets, has apparently existed for about 5 billion years, during its evolution (from birth from a gas nebula to its current state) it has made approximately 25 revolutions around the axis of rotation of the Galaxy. We can say that the age of the Sun is only 25 “galactic years”; let’s face it, it’s a blooming age...
The speed of movement of the Sun and its neighboring stars in their almost circular galactic orbits reaches 250 km/s. Superimposed on this regular motion around the galactic core are the chaotic, disorderly movements of stars. The speeds of such movements are much lower - about 10-50 km/s, and for objects different types they are different. The speeds are lowest for hot massive stars (6-8 km/s); for solar-type stars they are about 20 km/s. The lower these velocities, the more “flat” the distribution of a given type of star is.
On the scale that we used to visually represent the Solar System, the size of the Galaxy will be 60 million km - a value already quite close to the distance from the Earth to the Sun. From here it is clear that as we penetrate into increasingly more distant regions of the Universe, this scale is no longer suitable, since it loses clarity. Therefore, we will take a different scale. Let us mentally reduce the earth's orbit to the size of the innermost orbit of the hydrogen atom in the classical Bohr model. Let us recall that the radius of this orbit is 0.53x10 -8 cm. Then the nearest star will be at a distance of approximately 0.014 mm, the center of the Galaxy will be at a distance of about 10 cm, and the dimensions of our star system will be about 35 cm. The diameter of the Sun will have microscopic dimensions : 0.0046 A (angstrom unit of length equal to 10 -8 cm).
We have already emphasized that the stars are located at enormous distances from each other, and are thus practically isolated. In particular, this means that stars almost never collide with each other, although the motion of each of them is determined by the gravitational field created by all the stars in the Galaxy. If we consider the Galaxy as a certain region filled with gas, and the role of gas molecules and atoms is played by stars, then we must consider this gas to be extremely rarefied. In the solar vicinity, the average distance between stars is about 10 million times greater than the average diameter of stars. Meanwhile, under normal conditions in ordinary air, the average distance between molecules is only several tens of times more sizes the latter. To achieve the same degree of relative rarefaction, the air density would have to be reduced by at least 1018 times! Note, however, that in the central region of the Galaxy, where stellar density is relatively high, collisions between stars will occur from time to time. Here we should expect approximately one collision every million years, while in the “normal” regions of the Galaxy there have been virtually no collisions between stars in the entire history of the evolution of our stellar system, which is at least 10 billion years old.
For several decades now, astronomers have been persistently studying other star systems that are more or less similar to ours. This area of research is called "extragalactic astronomy." She now plays almost the leading role in astronomy. Over the past three decades, extragalactic astronomy has made astonishing advances. Little by little, the grandiose contours of the Metagalaxy began to emerge, of which our star system is included as a small particle. We still don’t know everything about the Metagalaxy. The enormous remoteness of objects creates very specific difficulties, which are resolved by using the most powerful means of observation in combination with in-depth theoretical research. Yet general structure Metagalaxies in last years mostly became clear.
We can define a Metagalaxy as a collection of star systems - galaxies moving in the vast spaces of the part of the Universe we observe. The galaxies closest to our star system are the famous Magellanic Clouds, clearly visible in the sky southern hemisphere as two large spots of approximately the same surface brightness as the Milky Way. The distance to the Magellanic Clouds is “only” about 200 thousand light years, which is quite comparable to the total extent of our Galaxy. Another galaxy “close” to us is the nebula in the constellation Andromeda. It is visible to the naked eye as a faint speck of light of 5th magnitude.
In fact, this is a huge star world, in terms of the number of stars and total mass three times greater than our Galaxy, which in turn is a giant among galaxies. The distance to the Andromeda nebula, or, as astronomers call it, M 31 (this means that in the well-known catalog of Messier nebulae it is listed as No. 31), is about 1800 thousand light years, which is about 20 times the size of the Galaxy. The M 31 nebula has a clearly defined spiral structure and in many of its characteristics is very similar to our Galaxy. Next to it are its small ellipsoidal satellites. Along with spiral systems (such galaxies are designated by the symbols Sa, Sb and Sc, depending on the nature of the development of the spiral structure; if there is a “bridge” passing through the core, the letter B is placed after the letter S), there are spheroidal and ellipsoidal ones, devoid of any traces of a spiral structure, as well as "wrong" galaxies good example which may serve as the Magellanic Clouds.
A huge number of galaxies are observed in large telescopes. If there are about 250 galaxies brighter than the visible 12th magnitude, then there are already about 50 thousand brighter than the 16th. The faintest objects, which at the limit can be photographed by a reflecting telescope with a mirror diameter of 5 m, have a magnitude of 24.5, for The Hubble orbital telescope limits this limit to objects of magnitude 30. It turns out that among the billions of such faint objects, the majority are galaxies. Many of them are distant from us at distances that light travels over billions of years. This means that the light that caused the plate to blacken was emitted by such a distant galaxy long before the Archean period geological history Earth!
The spectra of most galaxies resemble the sun; in both cases, individual dark absorption lines are observed against a fairly bright background. This is not unexpected, since the radiation of galaxies is the radiation of the billions of stars that comprise them, more or less similar to the Sun. Careful study of the spectra of galaxies many years ago led to a discovery of fundamental importance. The fact is that by the nature of the shift in the wavelength of any spectral line in relation to the laboratory standard, one can determine the speed of movement of the emitting source along the line of sight. In other words, it is possible to determine at what speed the source is approaching or moving away.
If the light source approaches, the spectral lines shift towards shorter wavelengths; if it moves away, towards longer ones. This phenomenon is called the "Doppler effect". It turned out that galaxies (with the exception of a few closest to us) have spectral lines that are always shifted to the long-wavelength part of the spectrum (“red shift” of the lines), and the greater the distance the galaxy is from us, the greater the magnitude of this shift.
This means that all galaxies are moving away from us, and the speed of “expansion” increases as the galaxies move away. It reaches enormous values. For example, the recession speed of the radio galaxy Cygnus A, found from the red shift, is close to 17 thousand km/s. For a long time, the record belonged to the very faint (in optical rays of the 20th magnitude) radio galaxy 3S 295. In 1960, its spectrum was obtained. It turned out that the well-known ultraviolet spectral line belonging to ionized oxygen is shifted to the orange region of the spectrum! From here it is easy to find that the speed of removal of this amazing star system is 138 thousand km/s, or almost half the speed of light! Radio galaxy 3S 295 is distant from us at a distance that light travels in 5 billion years. Thus, astronomers studied the light that was emitted when the Sun and planets were formed, and maybe even “a little” earlier... Since then, much more distant objects have been discovered.
Superimposed on the overall expansion of the galaxy system are the erratic velocities of individual galaxies, typically several hundred kilometers per second. This is why the galaxies closest to us do not exhibit a systematic redshift. After all, the speeds of random (so-called “peculiar”) movements for these galaxies are greater than the regular redshift speed. The latter increases as the galaxies move away by approximately 50 km/s, for every million parsecs. Therefore, for galaxies whose distances do not exceed several million parsecs, the random velocities exceed the receding velocity due to redshift. Among nearby galaxies, there are also those that are approaching us (for example, the Andromeda nebula M 31).
Galaxies are not uniformly distributed in metagalactic space, i.e. with constant density. They show a pronounced tendency to form separate groups or clusters. In particular, a group of about 20 galaxies close to us (including our Galaxy) forms the so-called “local system”. In turn, the local system is part of a large cluster of galaxies, the center of which is in that part of the sky onto which the constellation Virgo is projected. This cluster has several thousand members and is among the largest. In the space between clusters, the density of galaxies is tens of times less than inside the clusters.
Noteworthy is the difference between clusters of stars that form galaxies and clusters of galaxies. In the first case, the distances between cluster members are enormous compared to the sizes of the stars, while the average distances between galaxies in galaxy clusters are only several times larger than the sizes of the galaxies. On the other hand, the number of galaxies in clusters cannot be compared with the number of stars in galaxies. If we consider a collection of galaxies as a kind of gas, where the role of molecules is played by individual galaxies, then we must consider this medium to be extremely viscous.
What does the Metagalaxy look like in our model, where the earth's orbit is reduced to the size of the first orbit of a Bohr atom? On this scale, the distance to the Andromeda nebula will be slightly more than 6 m, the distance to the central part of the Virgo galaxy cluster, which includes our local galaxy system, will be about 120 m, and the size of the cluster itself will be of the same order. The radio galaxy Cygnus A will now be removed at a distance of 2.5 km, and the distance to the radio galaxy 3S 295 will reach 25 km...
We became acquainted in the most general form with the main structural features and scale of the Universe. It's like a frozen frame of her development. She was not always the way we see her now. Everything in the Universe changes: stars and nebulae appear, develop and “die”, the Galaxy develops in a natural way, the very structure and scale of the Metagalaxy changes.
Stairway to Infinity
How to determine the distance to the stars? How do we know that Alpha Centauri is about 4 light years away? After all, you can’t determine much by the brightness of a star as such—the brightness of a dim nearby star and a bright distant one can be the same. And yet there are many fairly reliable ways to determine the distances from Earth to the farthest corners of the Universe. Over the course of 4 years of operation, the Hipparchus astrometric satellite determined the distances of up to 118 thousand stars SPL
No matter what physicists say about three-dimensionality, six-dimensionality or even eleven-dimensionality of space, for an astronomer the observable Universe is always two-dimensional. What is happening in Space appears to us in a projection onto the celestial sphere, just as in a movie the entire complexity of life is projected onto a flat screen. On the screen, we can easily distinguish what is far from what is close due to our familiarity with the three-dimensional original, but in the two-dimensional scattering of stars there is no visual clue that allows us to turn it into a three-dimensional map suitable for plotting the course of an interstellar ship. Meanwhile, distances are the key to almost half of all astrophysics. Without them, how can you distinguish a nearby dim star from a distant but bright quasar? Only knowing the distance to an object can one evaluate its energy, and from here there is a direct path to understanding its physical nature.
A recent example of the uncertainty of cosmic distances is the problem of sources of gamma-ray bursts, short pulses of hard radiation that arrive at Earth approximately once a day from various directions. Initial estimates of their distance ranged from hundreds of astronomical units (tens of light hours) to hundreds of millions of light years. Accordingly, the spread in the models was also impressive - from the annihilation of antimatter comets on the outskirts of the Solar System to the explosions of neutron stars shaking the entire Universe and the birth of white holes. By the mid-1990s, more than a hundred had been proposed different explanations nature of gamma-ray bursts. Now that we have been able to estimate the distances to their sources, there are only two models left.
But how can you measure distance if you can’t reach the object with either a ruler or a locator beam? The triangulation method, widely used in conventional terrestrial geodesy, comes to the rescue. We select a segment of known length - the base, measure from its ends the angles at which a point that is inaccessible for one reason or another is visible, and then simple trigonometric formulas give the required distance. When we move from one end of the base to the other, the apparent direction of the point changes, it shifts against the background of distant objects. This is called parallax displacement, or parallax. Its value is smaller, the further away the object is, and the larger, the longer the base.
To measure distances to stars, one has to take the maximum base available to astronomers, equal to the diameter of the earth's orbit. The corresponding parallactic displacement of stars in the sky (strictly speaking, half of it) began to be called annual parallax. Tycho Brahe tried to measure it, who did not like Copernicus’ idea of the Earth’s rotation around the Sun, and he decided to check it - after all, parallaxes also prove the orbital motion of the Earth. The measurements taken had an accuracy impressive for the 16th century - about one minute of arc, but this was completely insufficient for measuring parallaxes, which Brahe himself did not realize and concluded that the Copernican system was incorrect.
The distance to star clusters is determined by the main sequence fitting method
The next attack on parallax was made in 1726 by the Englishman James Bradley, future director of the Greenwich Observatory. At first, it seemed that luck smiled on him: the star Gamma Draco, chosen for observation, actually oscillated around its average position over the course of a year with a swing of 20 seconds of arc. However, the direction of this shift was different from what was expected for parallaxes, and Bradley soon found the correct explanation: the speed of the Earth's orbit adds up to the speed of light coming from the star, and changes its apparent direction. In the same way, raindrops leave slanted tracks on bus windows. This phenomenon, called annual aberration, was the first direct evidence of the Earth's motion around the Sun, but had nothing to do with parallaxes.
Only a century later, the accuracy of goniometer instruments reached the required level. In the late 30s of the 19th century, as John Herschel put it, “the wall that prevented penetration into the stellar Universe was broken through almost simultaneously in three places.” In 1837, Vasily Yakovlevich Struve (at that time the director of the Dorpat Observatory, and later of the Pulkovo Observatory) published the Vega parallax he measured - 0.12 arcseconds. The following year, Friedrich Wilhelm Bessel reported that the parallax of the star 61st Cygnus was 0.3." And a year later, the Scottish astronomer Thomas Henderson, who worked in the Southern Hemisphere at Cape Good Hope, measured the parallax in the Alpha Centauri system - 1.16". However, it later turned out that this value was overestimated by 1.5 times and there is not a single star in the entire sky with a parallax of more than 1 arc second.
For distances measured by the parallactic method, a special unit of length was introduced - the parsec (from parallactic second, pc). One parsec contains 206,265 astronomical units, or 3.26 light years. It is from this distance that the radius of the earth’s orbit (1 astronomical unit = 149.5 million kilometers) is visible at an angle of 1 second. To determine the distance to a star in parsecs, you need to divide one by its parallax in seconds. For example, to the closest star system to us, Alpha Centauri 1/0.76 = 1.3 parsecs, or 270 thousand astronomical units. A thousand parsecs are called kiloparsecs (kpc), a million parsecs are called megaparsecs (Mpc), and a billion are called gigaparsecs (Gpc).
Measuring extremely small angles required technical sophistication and enormous diligence (Bessel, for example, processed more than 400 individual observations of the 61st Cygnus), but after the first breakthrough things went easier. By 1890, the parallaxes of already three dozen stars had been measured, and when photography began to be widely used in astronomy, the precise measurement of parallaxes was put on stream. Parallax measurements are the only method for directly determining distances to individual stars. But during ground-based observations, atmospheric interference does not allow the parallactic method to measure distances greater than 100 pc. For the Universe this is not a very large value. (“It’s not far here, a hundred parsecs,” as Gromozeka said.) Where geometric methods fail, photometric methods come to the rescue.
Geometric records
In recent years, the results of measuring distances to very compact sources of radio emission - masers - have been increasingly published. Their radiation occurs in the radio range, which makes it possible to observe them on radio interferometers capable of measuring the coordinates of objects with microsecond accuracy, unattainable in the optical range in which stars are observed. Thanks to masers, trigonometric methods can be applied not only to distant objects in our Galaxy, but also to other galaxies. For example, in 2005, Andreas Brunthaler (Germany) and his colleagues determined the distance to the M33 galaxy (730 kpc) by comparing the angular displacement of the masers with the rotation speed of this stellar system. A year later, Ye Xu (China) and his colleagues used classic method parallaxes to “local” maser sources in order to measure the distance (2 kpc) to one of the spiral arms of our Galaxy. Perhaps, J. Hernsteen (USA) and his colleagues managed to advance the furthest in 1999. By tracking the movement of masers in the accretion disk around the black hole at the core of the active galaxy NGC 4258, astronomers determined that this system is located at a distance of 7.2 Mpc from us. Today this is an absolute record for geometric methods.
Standard Astronomer Candles
The farther the source of radiation is from us, the dimmer it is. If you find out the true luminosity of an object, then by comparing it with the apparent brightness, you can find the distance. It was probably Huygens who was the first to apply this idea to measuring distances to stars. At night he observed Sirius, and during the day he compared its shine with a tiny hole in the screen that covered the Sun. Having chosen the size of the hole so that both brightnesses coincided, and comparing the angular values of the hole and the solar disk, Huygens concluded that Sirius is 27,664 times farther from us than the Sun. This is 20 times less than the real distance. The error was partly due to the fact that Sirius is actually much brighter than the Sun, and partly due to the difficulty of comparing brightness from memory.
A breakthrough in the field of photometric methods occurred with the advent of photography in astronomy. At the beginning of the 20th century, the Harvard College Observatory carried out large-scale work to determine the brightness of stars using photographic plates. Particular attention was paid to variable stars, the brightness of which fluctuates. Studying variable stars of a special class - Cepheids - in the Small Magellanic Cloud, Henrietta Leavitt noticed that the brighter they are, the longer the period of fluctuation in their brightness: stars with a period of several tens of days turned out to be about 40 times brighter than stars with a period of the order of a day.
Since all the Levitt Cepheids were in the same star system - the Small Magellanic Cloud - they could be considered to be at the same (albeit unknown) distance from us. This means that the difference in their apparent brightness is associated with real differences in luminosity. It remained to determine the distance to one Cepheid using a geometric method in order to calibrate the entire dependence and be able, by measuring the period, to determine the true luminosity of any Cepheid, and from it the distance to the star and the stellar system containing it.
But, unfortunately, there are no Cepheids in the vicinity of the Earth. The nearest of them - the North Star - is removed from the Sun, as we now know, by 130 pc, that is, it is beyond the reach of ground-based parallax measurements. This did not make it possible to build a bridge directly from parallaxes to Cepheids, and astronomers had to build a structure that is now figuratively called a distance ladder.
An intermediate stage on it became open star clusters, including from several tens to hundreds of stars connected total time and place of birth. If you plot the temperature and luminosity of all the stars in the cluster, most of points will fall on one inclined line (more precisely, a strip), which is called the main sequence. Temperature is determined with high accuracy from the star's spectrum, and luminosity is determined from its apparent brightness and distance. If the distance is unknown, the fact that all the stars in the cluster are almost equally distant from us comes to the rescue, so that within the cluster, apparent brightness can still be used as a measure of luminosity.
Since the stars are the same everywhere, the main sequences of all clusters must match. The differences are only due to the fact that they are at different distances. If we determine the distance to one of the clusters using a geometric method, we will find out what the “real” main sequence looks like, and then, by comparing data on other clusters with it, we will determine the distances to them. This method is called "main sequence fitting". The standard for him for a long time served as the Pleiades and Hyades, the distances to which were determined by the method of group parallaxes.
Fortunately for astrophysics, Cepheids have been discovered in about two dozen open clusters. Therefore, by measuring the distances to these clusters by adjusting the main sequence, it is possible to “stretch the ladder” to the Cepheids, which are on its third step.
Cepheids are very convenient as an indicator of distances: there are relatively many of them - they can be found in any galaxy and even in any globular cluster, and being giant stars, they are bright enough to measure intergalactic distances from them. Thanks to this, they have earned many loud epithets, such as “beacons of the Universe” or “milestones of astrophysics.” The Cepheid “line” extends up to 20 Mpc, which is about a hundred times the size of our Galaxy. They can no longer be distinguished even in the most powerful modern instruments, and to climb the fourth rung of the distance ladder, you need something brighter.
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METHODS FOR MEASUREMENT OF SPACE DISTANCES |
To the outskirts of the Universe
One of the most powerful extragalactic distance measurements is based on a pattern known as the Tully-Fisher relation: the brighter a spiral galaxy, the faster it rotates. When a galaxy is seen edge-on or at a significant tilt, half of its matter moves closer to us due to rotation, and half moves away, which leads to a broadening of the spectral lines due to the Doppler effect. The rotation speed is determined from this expansion, the luminosity is determined from it, and then, from a comparison with the visible brightness, the distance to the galaxy is determined. And, of course, to calibrate this method, we need galaxies whose distances have already been measured using Cepheids. The Tully-Fisher method is very long-range and covers galaxies hundreds of megaparsecs away from us, but it also has a limit, since it is not possible to obtain sufficiently high-quality spectra for galaxies that are too distant and faint.
At a slightly larger range of distances, another “standard candle” operates—type Ia supernovae. Outbursts of such supernovae are “same-type” thermonuclear explosions of white dwarfs with a mass slightly above the critical mass (1.4 solar masses). Therefore, there is no reason for them to vary greatly in power. Observations of such supernovae in nearby galaxies, the distances to which can be determined from Cepheids, seem to confirm this constancy, and therefore cosmic thermonuclear explosions are now widely used to determine distances. They are visible even billions of parsecs away from us, but you never know the distance to which galaxy will be measured, because it is not known in advance exactly where the next supernova will erupt.
So far, only one method allows us to move even further - redshifts. Its history, like the history of the Cepheids, begins simultaneously with the 20th century. In 1915, the American Vesto Slipher, studying the spectra of galaxies, noticed that in most of them the lines were red-shifted relative to the “laboratory” position. In 1924, the German Karl Wirtz noticed that this displacement is stronger, the smaller the angular dimensions of the galaxy. However, only Edwin Hubble managed to bring these data into a single picture in 1929. According to the Doppler effect, red shift of lines in the spectrum means that the object is moving away from us. By comparing the spectra of galaxies with distances to them determined from Cepheids, Hubble formulated a law: the speed at which a galaxy is moving away is proportional to its distance. The proportionality coefficient in this relationship is called the Hubble constant.
Thus, the expansion of the Universe was discovered, and with it the possibility of determining distances to galaxies from their spectra, of course, provided that the Hubble constant is tied to some other “rulers”. Hubble itself performed this alignment with an error of almost an order of magnitude, which was corrected only in the mid-1940s, when it became clear that Cepheids are divided into several types with different period-luminosity relationships. The calibration was performed again based on “classical” Cepheids, and only then the value of the Hubble constant became close to modern estimates: 50–100 km/s for each megaparsec of distance to the galaxy.
Now redshifts are used to determine distances to galaxies thousands of megaparsecs away from us. True, these distances are indicated in megaparsecs only in popular articles. The fact is that they depend on the model of the evolution of the Universe adopted in the calculations, and besides, in expanding space it is not entirely clear what distance is meant: the one at which the galaxy was at the moment of emission of radiation, or the one at which it is located at the moment of its reception on Earth, or the distance traveled by light on its way from the starting point to the final point. Therefore, astronomers prefer to indicate only the directly observed redshift value for distant objects, without converting it into megaparsecs.
Redshifts are the only method today for estimating “cosmological” distances comparable to the “size of the Universe,” and at the same time it is perhaps the most widely used technique. In July 2007, a catalog of redshifts of 77,418,767 galaxies was published. True, when creating it, a somewhat simplified automatic method for analyzing spectra was used, and therefore errors could creep into some values.
Team play
Geometric methods for measuring distances do not end with annual parallax, in which the apparent angular displacements of stars are compared with the movements of the Earth in its orbit. Another approach relies on the movement of the Sun and stars relative to each other. Let's imagine a star cluster flying past the Sun. According to the laws of perspective, the visible trajectories of its stars, like rails on the horizon, converge at one point - the radiant. Its position indicates at what angle the cluster flies to the line of sight. Knowing this angle, we can decompose the motion of the cluster stars into two components - along the line of sight and perpendicular to it along the celestial sphere - and determine the proportion between them. The radial velocity of stars in kilometers per second is measured using the Doppler effect and, taking into account the found proportion, the projection of the velocity onto the sky is calculated - also in kilometers per second. It remains to compare these linear speeds stars with angular angles determined from the results of long-term observations - and the distance will be known! This method works up to several hundred parsecs, but is applicable only to star clusters and is therefore called the group parallax method. This is how the distances to the Hyades and Pleiades were first measured.
Down the stairs leading up
While building our staircase to the outskirts of the Universe, we were silent about the foundation on which it rests. Meanwhile, the parallax method gives the distance not in standard meters, but in astronomical units, that is, in the radii of the earth’s orbit, the value of which was also not immediately determined. So let's look back and go down the ladder of cosmic distances to Earth.Probably the first to try to determine the distance of the Sun was Aristarchus of Samos, who proposed a heliocentric system of the world one and a half thousand years before Copernicus. He found that the Sun is 20 times farther from us than the Moon. This estimate, as we now know, was underestimated by a factor of 20, lasted until the Kepler era. Although he himself did not measure the astronomical unit, he already noted that the Sun should be much further than Aristarchus (and after him all the other astronomers) thought.
The first more or less acceptable estimate of the distance from the Earth to the Sun was obtained by Jean Dominique Cassini and Jean Richet. In 1672, during the opposition of Mars, they measured its position against the background stars from both Paris (Cassini) and Cayenne (Richet). The distance from France to French Guiana served as the basis of a parallactic triangle, from which they determined the distance to Mars, and then calculated the astronomical unit using the equations of celestial mechanics, obtaining a value of 140 million kilometers.
Over the next two centuries, the transit of Venus across the solar disk became the main tool for determining the scale of the solar system. Observing them simultaneously from different points globe, you can calculate the distance from Earth to Venus, and from here all other distances in the solar system. In the 18th-19th centuries, this phenomenon was observed four times: in 1761, 1769, 1874 and 1882. These observations were among the first international scientific projects. Large-scale expeditions were equipped (the English expedition of 1769 was led by the famous James Cook), special observation stations were created... And if in late XVIII century Russia only provided French scientists with the opportunity to observe the passage from its territory (from Tobolsk), then in 1874 and 1882 Russian scientists already accepted Active participation in research. Unfortunately, the exceptional complexity of observations has led to significant discrepancies in estimates of the astronomical unit - from approximately 147 to 153 million kilometers. A more reliable value - 149.5 million kilometers - was obtained only at the turn of the 19th-20th centuries from observations of asteroids. And finally, it must be taken into account that the results of all these measurements were based on knowledge of the length of the base, which was the radius of the Earth when measuring the astronomical unit. So ultimately the foundation of the cosmic distance ladder was laid by surveyors.
Only in the second half of the 20th century did scientists have at their disposal fundamentally new methods for determining cosmic distances - laser and radar. They made it possible to increase the accuracy of measurements in the Solar System by hundreds of thousands of times. The radar error for Mars and Venus is several meters, and the distance to the corner reflectors installed on the Moon is measured with an accuracy of centimeters. The currently accepted value of the astronomical unit is 149,597,870,691 meters.
The difficult fate of "Hipparchus"
Such radical progress in the measurement of the astronomical unit raised the question of distances to stars in a new way. The accuracy of parallax determination is limited by the Earth's atmosphere. Therefore, back in the 1960s, the idea arose to launch a goniometer instrument into space. It was realized in 1989 with the launch of the European astrometric satellite Hipparchus. This name is well-established, although formally not entirely correct translation English name HIPPARCOS, which is an abbreviation for High Precision Parallax Collecting Satellite (“satellite for collecting high-precision parallaxes”) and does not coincide with the English spelling of the name of the famous ancient Greek astronomer - Hipparchus, the author of the first star catalogue.The creators of the satellite set themselves a very ambitious task: to measure the parallaxes of more than 100 thousand stars with millisecond accuracy, that is, to “reach” stars located hundreds of parsecs from the Earth. It was necessary to clarify the distances to several open star clusters, in particular the Hyades and Pleiades. But most importantly, it became possible to “jump over the step” by directly measuring the distances to the Cepheids themselves.
The expedition began with troubles. Due to a failure in the upper stage, the Hipparchus did not enter the intended geostationary orbit and remained on an intermediate, highly elongated trajectory. European Space Agency specialists still managed to cope with the situation, and the orbital astrometric telescope successfully operated for 4 years. The processing of the results took the same amount of time, and in 1997 a star catalog with parallaxes and proper motions of 118,218 luminaries, including about two hundred Cepheids, was published.
Unfortunately, on a number of issues the desired clarity has not come. The most incomprehensible result was for the Pleiades - it was assumed that Hipparchus would clarify the distance, which was previously estimated at 130-135 parsecs, but in practice it turned out that Hipparchus corrected it, receiving a value of only 118 parsecs. Accepting a new value would require adjustments to both the theory of stellar evolution and the intergalactic distance scale. This would become a serious problem for astrophysics, and the distance to the Pleiades began to be carefully checked. By 2004, several groups, using independent methods, obtained estimates of the distance to the cluster in the range from 132 to 139 pc. Offensive voices began to be heard suggesting that the consequences of putting the satellite into the wrong orbit had not been completely eliminated. Thus, all the parallaxes he measured were called into question.
The Hipparchus team was forced to admit that the measurement results were generally accurate, but may need to be re-processed. The fact is that in space astrometry, parallaxes are not measured directly. Instead, Hipparchus measured the angles between numerous pairs of stars over the course of four years. These angles change both due to parallactic displacement and due to the stars’ own motions in space. To “pull out” exactly the parallax values from observations, rather complex mathematical processing is required. This is what I had to repeat. The new results were published at the end of September 2007, but it is not yet clear how much the situation has improved.
But the problems of “Hipparchus” do not end there. The Cepheid parallaxes he determined turned out to be insufficiently accurate for a reliable calibration of the period-luminosity relationship. Thus, the satellite failed to solve the second task facing it. Therefore, several new space astrometry projects are now being considered around the world. The closest to implementation is the European project Gaia, which is scheduled to launch in 2012. Its principle of operation is the same as that of “Hipparchus” - repeated measurements of angles between pairs of stars. However, thanks to powerful optics, it will be able to observe much dimmer objects, and the use of interferometry will increase the accuracy of measuring angles to tens of microarcseconds. It is assumed that Gaia will be able to measure kiloparsec distances with an error of no more than 20% and will determine the positions of about a billion objects over several years of operation. This will create a three-dimensional map of a significant part of the Galaxy.Aristotle's universe ended at nine distances from the Earth to the Sun. Copernicus believed that the stars were 1,000 times farther away than the Sun. Parallaxes pushed even the nearest stars light years away. At the very beginning of the 20th century, American astronomer Harlow Shapley, using Cepheids, determined that the diameter of the Galaxy (which he identified with the Universe) was measured in tens of thousands of light years, and thanks to Hubble, the boundaries of the Universe expanded to several gigaparsecs. How definitive are they?
Of course, at each step of the distance ladder there are larger or smaller errors, but in general the scales of the Universe are defined quite well, tested by various methods independent of each other and form a single consistent picture. So the modern boundaries of the Universe seem unshakable. However, this does not mean that one day we will not want to measure the distance from it to some neighboring Universe!
Shklovsky I.S., Dmitry Vibe. Earth (Sol III).
Based on materials from: www.vokrugsveta.ru, galspace.spb.ru,Shklovsky I.S. "Universe, life, mind" / Ed. N.S. Kardashev and V.I. Moroz. - 6th ed.
Part one ASTRONOMICAL ASPECT OF THE PROBLEM
1. The scale of the Universe and its structure If professional astronomers constantly and tangibly imagined the monstrous magnitude of cosmic distances and time intervals of the evolution of celestial bodies, it is unlikely that they could successfully develop the science to which they devoted their lives. The space-time scales familiar to us since childhood are so insignificant compared to cosmic ones that when it comes to consciousness, it literally takes your breath away. When dealing with any problem in space, an astronomer either solves a certain mathematical problem (this is most often done by specialists in celestial mechanics and theoretical astrophysicists), or improves instruments and observation methods, or builds in his imagination, consciously or unconsciously, some small model the space system under study. In this case, the main importance is a correct understanding of the relative sizes of the system being studied (for example, the ratio of the sizes of parts of a given space system, the ratio of the sizes of this system and others similar or dissimilar to it, etc.) and time intervals (for example, the ratio of the flow rate of a given process to the rate of occurrence of any other). The author of this book dealt quite a lot, for example, with the solar corona and the Galaxy. And they always seemed to him to be irregularly shaped spheroidal bodies of approximately the same size - something around 10 cm... Why 10 cm? This image arose subconsciously, simply because too often, while thinking about one or another issue of solar or galactic physics, the author drew the outlines of the objects of his thoughts in an ordinary notebook (in a box). I drew, trying to adhere to the scale of the phenomena. On one very interesting question, for example, it was possible to draw an interesting analogy between the solar corona and the Galaxy (or rather, the so-called “galactic corona”). Of course, the author of this book knew very well, so to speak, “intellectually,” that the dimensions of the galactic corona are hundreds of billions of times larger than the dimensions of the solar corona. But he calmly forgot about it. And if in a number of cases the large dimensions of the galactic corona acquired some fundamental significance (this also happened), this was taken into account formally and mathematically. And yet, visually, both “crowns” seemed equally small... If the author, in the process of this work, had indulged in philosophical reflections about the enormity of the size of the Galaxy, about the unimaginable rarefaction of the gas that makes up the galactic crown, about the insignificance of our little planet and our own existence and about other equally valid subjects, work on the problems of the solar and galactic coronas would stop automatically. .. May the reader forgive me this “lyrical digression”. I have no doubt that other astronomers had similar thoughts as they worked through their problems. It seems to me that sometimes it is useful to take a closer look at the “kitchen” of scientific work... If we want to discuss exciting questions about the possibility of intelligent life in the Universe on the pages of this book, then, first of all, we will need to get a correct idea of its spatio-temporal scale . Until relatively recently, the globe seemed huge to people. It took Magellan’s brave companions more than three years to make their first trip around the world 465 years ago, at the cost of incredible hardships. A little more than 100 years have passed since the time when the resourceful hero of Jules Verne’s science fiction novel, using the latest technological advances of the time, traveled around the world in 80 days. And only 26 years have passed since those memorable days for all mankind, when the first Soviet cosmonaut Gagarin circled the globe on the legendary Vostok spacecraft in 89 minutes. And people’s thoughts involuntarily turned to the vast expanses of space in which the small planet Earth was lost... Our Earth is one of the planets of the solar system. Compared to other planets, it is located quite close to the Sun, although it is not the closest. The average distance from the Sun to Pluto, the most distant planet in the solar system, is 40 times greater than the average distance from Earth to the Sun. It is currently unknown whether there are planets in the solar system that are even more distant from the Sun than Pluto. One can only say that if such planets exist, they are relatively small. Conventionally, the size of the Solar System can be taken to be 50-100 astronomical units *, or about 10 billion km. By our earthly scale, this is a very large value, approximately 1 million greater than the diameter of the Earth.Rice. 1. Planets of the Solar System
We can more clearly imagine the relative scale of the solar system as follows. Let the Sun be represented by a billiard ball with a diameter of 7 cm. Then the planet closest to the Sun - Mercury - is located on this scale at a distance of 280 cm. The Earth is at a distance of 760 cm, the giant planet Jupiter is at a distance of about 40 m, and the farthest planet - in many respects, Pluto is still mysterious - at a distance of about 300m. The dimensions of the globe on this scale are slightly more than 0.5 mm, the lunar diameter is slightly more than 0.1 mm, and the Moon’s orbit has a diameter of about 3 cm. Even the closest star to us, Proxima Centauri, is so far away from us that compared to it, interplanetary distances within the solar system seem like mere trifles. Readers, of course, know that a unit of length such as a kilometer is never used to measure interstellar distances**). This unit of measurement (as well as centimeter, inch, etc.) arose from the needs practical activities humanity on Earth. It is completely unsuitable for estimating cosmic distances that are too large compared to a kilometer. In popular literature, and sometimes in scientific literature, the “light year” is used as a unit of measurement to estimate interstellar and intergalactic distances. This is the distance that light, moving at a speed of 300 thousand km/s, travels in a year. It is easy to see that a light year is equal to 9.46 x 10 12 km, or about 10,000 billion km. In the scientific literature, a special unit called the “parsec” is usually used to measure interstellar and intergalactic distances;
1 parsec (pc) is equal to 3.26 light years. A parsec is defined as the distance from which the radius of the Earth's orbit is visible at an angle of 1 second. arcs. This is a very small angle. Suffice it to say that from this angle a one-kopeck coin is visible from a distance of 3 km.
Rice. 2. Globular cluster 47 Tucanae
None of the stars - the closest neighbors of the Solar System - are closer to us than 1 pc. For example, the mentioned Proxima Centauri is located at a distance of about 1.3 pc from us. On the scale in which we depicted the Solar System, this corresponds to 2 thousand km. All this well illustrates the great isolation of our Solar system from surrounding stellar systems; some of these systems may have many similarities with it. But the stars surrounding the Sun and the Sun itself constitute only an insignificant part of the gigantic group of stars and nebulae, which is called the “Galaxy”. We see this cluster of stars on clear moonless nights as a stripe of the Milky Way crossing the sky. The galaxy has a rather complex structure. In the first, roughest approximation, we can assume that the stars and nebulae of which it consists fill a volume shaped like a highly compressed ellipsoid of revolution. Often in popular literature the shape of the Galaxy is compared to a biconvex lens. In reality, everything is much more complicated, and the picture drawn is too rough. In fact, it turns out that different types of stars concentrate in completely different ways towards the center of the Galaxy and towards its “equatorial plane”. For example, gaseous nebulae, as well as very hot massive stars, are strongly concentrated towards the equatorial plane of the Galaxy (in the sky this plane corresponds to a large circle passing through the central parts of the Milky Way). At the same time, they do not show a significant concentration towards the galactic center. On the other hand, some types of stars and star clusters (the so-called “globular clusters”, Fig. 2) show almost no concentration towards the equatorial plane of the Galaxy, but are characterized by a huge concentration towards its center. Between these two extreme types of spatial distribution (which astronomers call "flat" and "spherical") are all the intermediate cases. However, it turns out that the bulk of the stars in the Galaxy are located in a giant disk, the diameter of which is about 100 thousand light years and the thickness is about 1500 light years. This disk contains slightly more than 150 billion stars of various types. Our Sun is one of these stars, located on the periphery of the Galaxy close to its equatorial plane (more precisely, “only” at a distance of about 30 light years - a value quite small compared to the thickness of the stellar disk). The distance from the Sun to the core of the Galaxy (or its center) is about 30 thousand km. light years. Stellar density in the Galaxy is very uneven. It is highest in the region of the galactic core, where, according to the latest data, it reaches 2 thousand stars per cubic parsec, which is almost 20 thousand times more than the average stellar density in the vicinity of the Sun ***. In addition, stars tend to form distinct groups or clusters. A good example of such a cluster is the Pleiades, which is visible in our winter sky (Figure 3). The Galaxy also contains structural details on a much larger scale. Research in recent years has proven that nebulae, as well as hot massive stars, are distributed along the branches of the spiral. The spiral structure is especially clearly visible in other star systems - galaxies (with a small letter, in contrast to our star system - Galaxies). One of these galaxies is shown in Fig. 4. Establishing the spiral structure of the Galaxy in which we ourselves find ourselves has proven extremely difficult.
Rice. 3. Photo of the Pleiades star cluster
Rice. 4. Spiral Galaxy NGC 5364
Stars and nebulae within the Galaxy move in quite complex ways. First of all, they participate in the rotation of the Galaxy around an axis perpendicular to its equatorial plane. This rotation is not the same as that of a solid body: different parts of the Galaxy have different periods of rotation. Thus, the Sun and the stars surrounding it in a huge area several hundred light years in size complete a full revolution in about 200 million years. Since the Sun, together with its family of planets, has apparently existed for about 5 billion years, during its evolution (from birth from a gas nebula to its current state) it has made approximately 25 revolutions around the axis of rotation of the Galaxy. We can say that the age of the Sun is only 25 “galactic years”; let’s face it, it’s a blooming age... The speed of movement of the Sun and its neighboring stars in their almost circular galactic orbits reaches 250 km/s ****. Superimposed on this regular motion around the galactic core are the chaotic, disorderly movements of stars. The speeds of such movements are much lower - about 10-50 km/s, and they are different for objects of different types. The speeds are lowest for hot massive stars (6-8 km/s); for solar-type stars they are about 20 km/s. The lower these velocities, the more “flat” the distribution of a given type of star is. On the scale that we used to visually represent the Solar System, the size of the Galaxy will be 60 million km - a value already quite close to the distance from the Earth to the Sun. From here it is clear that as we penetrate into increasingly more distant regions of the Universe, this scale is no longer suitable, since it loses clarity. Therefore, we will take a different scale. Let us mentally reduce the earth's orbit to the size of the innermost orbit of the hydrogen atom in the classical Bohr model. Let us recall that the radius of this orbit is 0.53x10 -8 cm. Then the nearest star will be at a distance of approximately 0.014 mm, the center of the Galaxy will be at a distance of about 10 cm, and the dimensions of our star system will be about 35 cm. The diameter of the Sun will have microscopic dimensions : 0.0046 A (angstrom unit of length equal to 10 -8 cm).
We have already emphasized that the stars are located at enormous distances from each other, and are thus practically isolated. In particular, this means that stars almost never collide with each other, although the motion of each of them is determined by the gravitational field created by all the stars in the Galaxy. If we consider the Galaxy as a certain region filled with gas, and the role of gas molecules and atoms is played by stars, then we must consider this gas to be extremely rarefied. In the solar vicinity, the average distance between stars is about 10 million times greater than the average diameter of stars. Meanwhile, under normal conditions in ordinary air, the average distance between molecules is only several tens of times greater than the size of the latter. To achieve the same degree of relative rarefaction, the air density would have to be reduced by at least 1018 times! Note, however, that in the central region of the Galaxy, where stellar density is relatively high, collisions between stars will occur from time to time. Here we should expect approximately one collision every million years, while in the “normal” regions of the Galaxy there have been virtually no collisions between stars in the entire history of the evolution of our stellar system, which is at least 10 billion years old (see Chapter 9). ).
We have briefly outlined the scale and most general structure of the star system to which our Sun belongs. At the same time, the methods with the help of which, over the course of many years, several generations of astronomers, step by step, recreated a majestic picture of the structure of the Galaxy, were not considered at all. Other books are devoted to this important problem, to which we refer interested readers (for example, B.A. Vorontsov-Velyaminov “Essays on the Universe”, Yu.N. Efremov “Into the Depths of the Universe”). Our task is to give only the most general picture of the structure and development of individual objects in the Universe. This picture is absolutely necessary for understanding this book.
Rice. 5. Andromeda Nebula with satellites
For several decades now, astronomers have been persistently studying other star systems that are more or less similar to ours. This area of research is called "extragalactic astronomy." She now plays almost the leading role in astronomy. Over the past three decades, extragalactic astronomy has made astonishing advances. Little by little, the grandiose contours of the Metagalaxy began to emerge, of which our stellar system is included as a small particle. We still don’t know everything about the Metagalaxy. The enormous remoteness of objects creates very specific difficulties, which are resolved by using the most powerful means of observation in combination with in-depth theoretical research. Yet the general structure of the Metagalaxy has largely become clear in recent years. We can define a Metagalaxy as a collection of star systems - galaxies moving in the vast spaces of the part of the Universe we observe. The galaxies closest to our star system are the famous Magellanic Clouds, clearly visible in the sky of the southern hemisphere as two large spots of approximately the same surface brightness as the Milky Way. The distance to the Magellanic Clouds is “only” about 200 thousand light years, which is quite comparable to the total extent of our Galaxy. Another galaxy “close” to us is the nebula in the constellation Andromeda. It is visible to the naked eye as a faint speck of light of 5th magnitude *****. In fact, this is a huge star world, in terms of the number of stars and total mass three times greater than our Galaxy, which in turn is a giant among galaxies. The distance to the Andromeda nebula, or, as astronomers call it, M 31 (this means that in the well-known catalog of Messier nebulae it is listed as No. 31), is about 1800 thousand light years, which is about 20 times the size of the Galaxy. The M 31 nebula has a clearly defined spiral structure and in many of its characteristics is very similar to our Galaxy. Next to it are its small ellipsoidal satellites (Fig. 5). In Fig. Figure 6 shows photographs of several galaxies relatively close to us. Noteworthy is the wide variety of their forms. Along with spiral systems (such galaxies are designated by the symbols Sа, Sb and Sс depending on the nature of the development of the spiral structure; if there is a “bridge” passing through the core (Fig. 6a), the letter B is placed after the letter S), there are spheroidal and ellipsoidal ones, devoid of any traces spiral structure, as well as “irregular” galaxies, a good example of which are the Magellanic Clouds. A huge number of galaxies are observed in large telescopes. If there are about 250 galaxies brighter than the visible 12th magnitude, then there are already about 50 thousand brighter than the 16th. The faintest objects that can be photographed at the limit by a reflecting telescope with a mirror diameter of 5 m are 24.5th magnitude. It turns out that among the billions of such faint objects, the majority are galaxies. Many of them are distant from us at distances that light travels over billions of years. This means that the light that caused the blackening of the plate was emitted by such a distant galaxy long before the Archean period of the geological history of the Earth!
Rice. 6a. Cross spiral galaxy
Rice. 6b. Galaxy NGC 4594
Rice. 6s. Galaxies Magellanic clouds
Sometimes among the galaxies you come across amazing objects, for example, “radio galaxies”. These are star systems that emit huge amounts of energy in the radio range. For some radio galaxies, the flux of radio emission is several times higher than the flux of optical radiation, although in the optical range their luminosity is very high - several times greater than the total luminosity of our Galaxy. Let us recall that the latter consists of the radiation of hundreds of billions of stars, many of which, in turn, radiate much stronger than the Sun. Classic example such a radio galaxy is the famous object Cygnus A. In the optical range, these are two insignificant specks of light of the 17th magnitude (Fig. 7). In fact, their luminosity is very high, about 10 times greater than that of our Galaxy. This system seems weak because it is located at a huge distance from us - 600 million light years. However, the flux of radio emission from Cygnus A at meter waves is so great that it even exceeds the flux of radio emission from the Sun (during periods when there are no sunspots on the Sun). But the Sun is very close - the distance to it is “only” 8 light minutes; 600 million years - and 8 minutes! But radiation fluxes, as is known, are inversely proportional to the squares of the distances! The spectra of most galaxies resemble the sun; in both cases, individual dark absorption lines are observed against a fairly bright background. This is not unexpected, since the radiation of galaxies is the radiation of the billions of stars that comprise them, more or less similar to the Sun. Careful study of the spectra of galaxies many years ago led to a discovery of fundamental importance. The fact is that by the nature of the shift in the wavelength of any spectral line in relation to the laboratory standard, one can determine the speed of movement of the emitting source along the line of sight. In other words, it is possible to determine at what speed the source is approaching or moving away.
Rice. 7. Radio galaxy Cygnus A
If the light source approaches, the spectral lines shift towards shorter wavelengths; if it moves away, towards longer ones. This phenomenon is called the "Doppler effect". It turned out that galaxies (with the exception of a few closest to us) have spectral lines that are always shifted to the long-wavelength part of the spectrum (“red shift” of the lines), and the greater the distance the galaxy is from us, the greater the magnitude of this shift. This means that all galaxies are moving away from us, and the speed of “expansion” increases as the galaxies move away. It reaches enormous values. For example, the recession speed of the radio galaxy Cygnus A, found from the red shift, is close to 17 thousand km/s. Twenty-five years ago, the record belonged to the very faint (in optical rays of the 20th magnitude) radio galaxy 3S 295. In 1960, its spectrum was obtained. It turned out that the well-known ultraviolet spectral line belonging to ionized oxygen is shifted to the orange region of the spectrum! From here it is easy to find that the speed of removal of this amazing star system is 138 thousand km/s, or almost half the speed of light! Radio galaxy 3S 295 is distant from us at a distance that light travels in 5 billion years. Thus, astronomers studied the light that was emitted when the Sun and planets were formed, and maybe even “a little” earlier... Since then, even more distant objects have been discovered (Chapter 6). We will not touch upon the reasons for the expansion of a system consisting of a huge number of galaxies here. This complex question is the subject of modern cosmology. However, the very fact of the expansion of the Universe has great importance to analyze the development of life in it (chapter 7). Superimposed on the overall expansion of the galaxy system are the erratic velocities of individual galaxies, typically several hundred kilometers per second. This is why the galaxies closest to us do not exhibit a systematic redshift. After all, the speeds of random (so-called “peculiar”) movements for these galaxies are greater than the regular redshift speed. The latter increases as the galaxies move away by approximately 50 km/s, for every million parsecs. Therefore, for galaxies whose distances do not exceed several million parsecs, the random velocities exceed the receding velocity due to the redshift. Among nearby galaxies, there are also those that are approaching us (for example, the Andromeda nebula M 31). Galaxies are not uniformly distributed in metagalactic space, i.e. with constant density. They show a pronounced tendency to form separate groups or clusters. In particular, a group of about 20 galaxies close to us (including our Galaxy) forms the so-called “local system”. In turn, the local system is part of a large cluster of galaxies, the center of which is in that part of the sky on which the Virgo constellation is projected. This cluster has several thousand members and is among the largest. In Fig. Figure 8 shows a photograph of the famous galaxy cluster in the constellation Corona Borealis, numbering hundreds of galaxies. In the space between clusters, the density of galaxies is tens of times less than inside the clusters.
Rice. 8. Cluster of galaxies in the constellation Corona Borealis
Noteworthy is the difference between clusters of stars that form galaxies and clusters of galaxies. In the first case, the distances between cluster members are enormous compared to the sizes of the stars, while the average distances between galaxies in galaxy clusters are only several times larger than the sizes of the galaxies. On the other hand, the number of galaxies in clusters cannot be compared with the number of stars in galaxies. If we consider a collection of galaxies as a kind of gas, where the role of molecules is played by individual galaxies, then we must consider this medium to be extremely viscous.
Table 1
|
Big Bang |
|
|
Formation of galaxies (z~10) |
|
|
Formation of the Solar System |
|
|
Earth Education |
|
|
The emergence of life on Earth |
|
|
Education ancient rocks on the ground |
|
|
The appearance of bacteria and blue-green algae |
|
|
The emergence of photosynthesis |
|
|
The first cells with a nucleus |
|
| Sunday | Monday | Tuesday | Wednesday | Thursday | Friday | Saturday |
| The emergence of an oxygen atmosphere on Earth | Violent volcanic activity on Mars | |||||
| The first worms | Ocean plankton Trilobites | Ordovician The first fish | Silur Plants colonize land | |||
| Devonian The first insects Animals colonize land | The first amphibians and winged insects | Carbon The first trees The first reptiles | Permian The first dinosaurs | Beginning of the Mesozoic | Triassic First mammals | Yura The first birds |
| Chalk First flowers | Tertiary period First primates | First hominids | Quaternary period First People (~22:30) |
- * Astronomical unit - the average distance from the Earth to the Sun, equal to 149,600 thousand km.
- ** Perhaps only the speeds of stars and planets in astronomy are expressed in units of “kilometers per second”.
- *** In the very center of the galactic core, in a region 1 pc across, there are apparently several million stars.
- **** It is useful to remember a simple rule: a speed of 1 pc in 1 million years is almost equal to a speed of 1 km/s. We leave it to the reader to verify this.
- ***** The flux of radiation from stars is measured by so-called “stellar magnitudes”. By definition, the flux from an (i+1)th magnitude star is 2.512 times less than that from a star i-th magnitude. Stars fainter than 6th magnitude are not visible to the naked eye. The most bright stars have a negative magnitude (for example, Sirius has a magnitude of -1.5).
We can more clearly imagine the relative scale of the solar system as follows. Let the Sun be represented by a billiard ball with a diameter of 7 cm. Then the planet closest to the Sun, Mercury, is at a distance of 280 cm from it on this scale. The Earth is at a distance of 760 cm, the giant planet Jupiter is at a distance of about 40 m, and the farthest planet is in many respects, Pluto is still mysterious - at a distance of about 300m. The dimensions of the globe on this scale are slightly larger than 0.5 mm, the lunar diameter is slightly larger than 0.1 mm, and the orbit of the Moon has a diameter of about 3 cm.
The scale of the Universe and its structure
If professional astronomers constantly and tangibly imagined the monstrous magnitude of cosmic distances and time intervals of the evolution of celestial bodies, it is unlikely that they could successfully develop the science to which they devoted their lives. The space-time scales familiar to us since childhood are so insignificant compared to cosmic ones that when it comes to consciousness, it literally takes your breath away. When dealing with any problem in space, an astronomer either solves a certain mathematical problem (this is most often done by specialists in celestial mechanics and theoretical astrophysicists), or improves instruments and observation methods, or builds in his imagination, consciously or unconsciously, some small model the space system under study. In this case, the main importance is a correct understanding of the relative sizes of the system being studied (for example, the ratio of the sizes of parts of a given space system, the ratio of the sizes of this system and others similar or dissimilar to it, etc.) and time intervals (for example, the ratio of the flow rate of a given process to the rate of occurrence of any other).
The author of this book dealt quite a lot, for example, with the solar corona and the Galaxy. And they always seemed to him to be irregularly shaped spheroidal bodies of approximately the same size - something around 10 cm... Why 10 cm? This image arose subconsciously, simply because too often, while thinking about one or another issue of solar or galactic physics, the author drew the outlines of the objects of his thoughts in an ordinary notebook (in a box). I drew, trying to adhere to the scale of the phenomena. On one very interesting question, for example, it was possible to draw an interesting analogy between the solar corona and the Galaxy (or rather, the so-called galactic corona). Of course, the author of this book knew very well, so to speak, intellectually, that the dimensions of the galactic corona are hundreds of billions of times larger than the dimensions of the solar corona. But he calmly forgot about it. And if in a number of cases the large dimensions of the galactic corona acquired some fundamental significance (this also happened), this was taken into account formally and mathematically. And still, visually, both crowns seemed equally small...
If the author, in the process of this work, indulged in philosophical reflections about the enormity of the size of the Galaxy, about the unimaginable rarefaction of the gas that makes up the galactic crown, about the insignificance of our little planet and our own existence, and about other other no less correct subjects, work on the problems of solar and galactic Corona would stop automatically...
Let the reader forgive me this lyrical digression. I have no doubt that other astronomers had similar thoughts as they worked through their problems. It seems to me that sometimes it is useful to become more familiar with the kitchen of scientific work...
If we want to discuss on the pages of this book exciting questions about the possibility of intelligent life in the Universe, then, first of all, we will need to get a correct idea of its spatio-temporal scale. Until relatively recently, the globe seemed huge to people. It took Magellan’s brave companions more than three years to make their first trip around the world 465 years ago, at the cost of incredible hardships. A little more than 100 years have passed since the time when the resourceful hero of Jules Verne’s science fiction novel, using the latest technological advances of the time, traveled around the world in 80 days. And only 26 years have passed since those memorable days for all mankind, when the first Soviet cosmonaut Gagarin circled the globe on the legendary Vostok spacecraft in 89 minutes. And people’s thoughts involuntarily turned to the vast expanses of space, in which the small planet Earth was lost...
Our Earth is one of the planets in the solar system. Compared to other planets, it is located quite close to the Sun, although it is not the closest. The average distance from the Sun to Pluto, the farthest planet in the solar system, is 40 times greater than the average distance from Earth to the Sun. It is currently unknown whether there are planets in the solar system that are even more distant from the Sun than Pluto. One can only say that if such planets exist, they are relatively small. Conventionally, the size of the Solar System can be taken to be 50-100 astronomical units*, or about 10 billion km.
By our earthly scale, this is a very large value, approximately 1 million greater than the diameter of the Earth.
We can more clearly imagine the relative scale of the solar system as follows. Let the Sun be represented by a billiard ball with a diameter of 7 cm. Then the planet closest to the Sun, Mercury, is at a distance of 280 cm from it on this scale. The Earth is at a distance of 760 cm, the giant planet Jupiter is at a distance of about 40 m, and the farthest planet is in many respects, Pluto is still mysterious - at a distance of about 300m. The dimensions of the globe on this scale are slightly larger than 0.5 mm, the lunar diameter is slightly more than 0.1 mm, and the Moon’s orbit has a diameter of about 3 cm. Even the closest star to us, Proxima Centauri, is so far away from us that compared to it, interplanetary distances within the solar system seem like mere trifles. Readers, of course, know that a unit of length such as a kilometer is never used to measure interstellar distances**).
This unit of measurement (as well as the centimeter, inch, etc.) arose from the needs of the practical activities of mankind on Earth. It is completely unsuitable for estimating cosmic distances that are too large compared to a kilometer.
In popular literature, and sometimes in scientific literature, the light year is used as a unit of measurement to estimate interstellar and intergalactic distances. This is the distance that light, moving at a speed of 300 thousand km/s, travels in a year. It is easy to see that a light year is equal to 9.46 × 1012 km, or about 10,000 billion km.
In the scientific literature, a special unit called the parsec is usually used to measure interstellar and intergalactic distances;
1 parsec (pc) is equal to 3.26 light years. A parsec is defined as the distance from which the radius of the Earth's orbit is visible at an angle of 1 second. arcs. This is a very small angle. Suffice it to say that from this angle a one-kopeck coin is visible from a distance of 3 km.
None of the stars - the closest neighbors of the Solar System - are closer to us than 1 pc. For example, the mentioned Proxima Centauri is located at a distance of about 1.3 pc from us. On the scale in which we depicted the Solar System, this corresponds to 2 thousand km. All this well illustrates the great isolation of our Solar system from surrounding stellar systems; some of these systems may have many similarities with it.
But the stars surrounding the Sun and the Sun itself constitute only an insignificant part of the gigantic group of stars and nebulae called the Galaxy. We see this cluster of stars on clear moonless nights as a stripe of the Milky Way crossing the sky. The galaxy has a rather complex structure. In the first, roughest approximation, we can assume that the stars and nebulae of which it consists fill a volume shaped like a highly compressed ellipsoid of revolution. Often in popular literature the shape of the Galaxy is compared to a biconvex lens. In reality, everything is much more complicated, and the picture drawn is too rough. In fact, it turns out that different types of stars concentrate in completely different ways towards the center of the Galaxy and towards its equatorial plane. For example, gaseous nebulae, as well as very hot massive stars, are strongly concentrated towards the equatorial plane of the Galaxy (in the sky this plane corresponds to a large circle passing through the central parts of the Milky Way). At the same time, they do not show a significant concentration towards the galactic center. On the other hand, some types of stars and star clusters (the so-called globular clusters, Fig. 2) show almost no concentration towards the equatorial plane of the Galaxy, but are characterized by a huge concentration towards its center. Between these two extreme types of spatial distribution (which astronomers call flat and spherical) lie all the intermediate cases. However, it turns out that the bulk of the stars in the Galaxy are located in a giant disk, the diameter of which is about 100 thousand light years and the thickness is about 1500 light years. This disk contains slightly more than 150 billion stars of various types. Our Sun is one of these stars, located on the periphery of the Galaxy close to its equatorial plane (more precisely, only at a distance of about 30 light years - a value quite small compared to the thickness of the stellar disk).
The distance from the Sun to the core of the Galaxy (or its center) is about 30 thousand light years. Stellar density in the Galaxy is very uneven. It is highest in the region of the galactic core, where, according to the latest data, it reaches 2 thousand stars per cubic parsec, which is almost 20 thousand times more than the average stellar density in the vicinity of the Sun***. In addition, stars tend to form distinct groups or clusters. A good example of such a cluster is the Pleiades, which is visible in our winter sky (Figure 3).
The Galaxy also contains structural details on a much larger scale. Research in recent years has proven that nebulae, as well as hot massive stars, are distributed along the branches of the spiral. The spiral structure is especially clearly visible in other star systems - galaxies (with a small letter, in contrast to our star system - Galaxies). One of these galaxies is shown in Fig. 4. Establishing the spiral structure of the Galaxy in which we ourselves find ourselves has proven extremely difficult.
Stars and nebulae within the Galaxy move in quite complex ways. First of all, they participate in the rotation of the Galaxy around an axis perpendicular to its equatorial plane. This rotation is not the same as that of a solid body: different parts of the Galaxy have different periods of rotation. Thus, the Sun and the stars surrounding it in a huge area several hundred light years in size complete a full revolution in about 200 million years. Since the Sun, together with its family of planets, has apparently existed for about 5 billion years, during its evolution (from birth from a gas nebula to its current state) it has made approximately 25 revolutions around the axis of rotation of the Galaxy. We can say that the age of the Sun is only 25 galactic years; let’s face it, it’s a blooming age...
The speed of movement of the Sun and its neighboring stars in their almost circular galactic orbits reaches 250 km/s****. Superimposed on this regular motion around the galactic core are the chaotic, disorderly movements of stars. The speeds of such movements are much lower - about 10-50 km/s, and they are different for objects of different types. The speeds are lowest for hot massive stars (6-8 km/s); for solar-type stars they are about 20 km/s. The lower these velocities, the flatter the distribution of a given type of star.
On the scale that we used to visually represent the Solar System, the size of the Galaxy will be 60 million km - a value already quite close to the distance from the Earth to the Sun. From here it is clear that as we penetrate into increasingly more distant regions of the Universe, this scale is no longer suitable, since it loses clarity. Therefore, we will take a different scale. Let us mentally reduce the earth's orbit to the size of the innermost orbit of the hydrogen atom in the classical Bohr model. Let us recall that the radius of this orbit is 0.53 × 10-8 cm. Then the nearest star will be at a distance of approximately 0.014 mm, the center of the Galaxy will be at a distance of about 10 cm, and the dimensions of our star system will be about 35 cm. The diameter of the Sun will be microscopic dimensions: 0.0046 A (angstrom unit of length equal to 10-8 cm).
We have already emphasized that the stars are located at enormous distances from each other, and are thus practically isolated. In particular, this means that stars almost never collide with each other, although the motion of each of them is determined by the gravitational field created by all the stars in the Galaxy. If we consider the Galaxy as a certain region filled with gas, and the role of gas molecules and atoms is played by stars, then we must consider this gas to be extremely rarefied. In the solar vicinity, the average distance between stars is about 10 million times greater than the average diameter of stars. Meanwhile, under normal conditions in ordinary air, the average distance between molecules is only several tens of times greater than the size of the latter. To achieve the same degree of relative rarefaction, the air density would have to be reduced by at least 1018 times! Note, however, that in the central region of the Galaxy, where stellar density is relatively high, collisions between stars will occur from time to time. Here we should expect approximately one collision every million years, while in normal regions of the Galaxy there have been practically no collisions between stars in the entire history of the evolution of our stellar system, which is at least 10 billion years old (see Chapter 9).
We have briefly outlined the scale and most general structure of the star system to which our Sun belongs. At the same time, the methods with the help of which, over the course of many years, several generations of astronomers, step by step, recreated a majestic picture of the structure of the Galaxy, were not considered at all. Other books are devoted to this important problem, to which we refer interested readers (for example, B.A. Vorontsov-Velyaminov Essays on the Universe, Yu.N. Efremov In the Depths of the Universe). Our task is to give only the most general picture of the structure and development of individual objects in the Universe. This picture is absolutely necessary for understanding this book.
For several decades now, astronomers have been persistently studying other star systems that are more or less similar to ours. This area of research is called extragalactic astronomy. She now plays almost the leading role in astronomy. Over the past three decades, extragalactic astronomy has made astonishing advances. Little by little, the grandiose contours of the Metagalaxy began to emerge, of which our stellar system is included as a small particle. We still don’t know everything about the Metagalaxy. The enormous remoteness of objects creates very specific difficulties, which are resolved by using the most powerful means of observation in combination with in-depth theoretical research. Yet the general structure of the Metagalaxy has largely become clear in recent years.
We can define a Metagalaxy as a collection of star systems - galaxies moving in the vast spaces of the part of the Universe we observe. The galaxies closest to our star system are the famous Magellanic Clouds, clearly visible in the sky of the southern hemisphere as two large spots of approximately the same surface brightness as the Milky Way. The distance to the Magellanic Clouds is only about 200 thousand light years, which is quite comparable to the total extent of our Galaxy. Another galaxy close to us is the nebula in the constellation Andromeda. It is visible to the naked eye as a faint speck of light of 5th magnitude*****.
In fact, this is a huge star world, in terms of the number of stars and total mass three times greater than our Galaxy, which in turn is a giant among galaxies. The distance to the Andromeda nebula, or, as astronomers call it, M 31 (this means that in the well-known catalog of Messier nebulae it is listed as No. 31), is about 1800 thousand light years, which is about 20 times the size of the Galaxy. The M 31 nebula has a clearly defined spiral structure and in many of its characteristics is very similar to our Galaxy. Next to it are its small ellipsoidal satellites (Fig. 5). In Fig. Figure 6 shows photographs of several galaxies relatively close to us. Noteworthy is the wide variety of their forms. Along with spiral systems (such galaxies are designated by the symbols Sа, Sb and Sс depending on the nature of the development of the spiral structure; if there is a bridge passing through the core (Fig. 6a), the letter B is placed after the letter S), there are spheroidal and ellipsoidal ones, devoid of any traces of a spiral structure , as well as irregular galaxies, of which the Magellanic Clouds are a good example.
A huge number of galaxies are observed in large telescopes. If there are about 250 galaxies brighter than the visible 12th magnitude, then there are already about 50 thousand brighter than the 16th. The faintest objects that can be photographed at the limit by a reflecting telescope with a mirror diameter of 5 m are 24.5th magnitude. It turns out that among the billions of such faint objects, the majority are galaxies. Many of them are distant from us at distances that light travels over billions of years. This means that the light that caused the blackening of the plate was emitted by such a distant galaxy long before the Archean period of the geological history of the Earth!
Sometimes among galaxies you come across amazing objects, such as radio galaxies. These are star systems that emit huge amounts of energy in the radio range. For some radio galaxies, the flux of radio emission is several times higher than the flux of optical radiation, although in the optical range their luminosity is very high - several times greater than the total luminosity of our Galaxy. Let us recall that the latter consists of the radiation of hundreds of billions of stars, many of which, in turn, radiate much stronger than the Sun. A classic example of such a radio galaxy is the famous object Cygnus A. In the optical range, these are two insignificant specks of light of the 17th magnitude (Fig. 7). In fact, their luminosity is very high, about 10 times greater than that of our Galaxy. This system seems weak because it is located at a huge distance from us - 600 million light years. However, the flux of radio emission from Cygnus A at meter waves is so great that it even exceeds the flux of radio emission from the Sun (during periods when there are no sunspots on the Sun). But the Sun is very close - the distance to it is only 8 light minutes; 600 million years - and 8 minutes! But radiation fluxes, as is known, are inversely proportional to the squares of the distances!
The spectra of most galaxies resemble the sun; in both cases, individual dark absorption lines are observed against a fairly bright background. This is not unexpected, since the radiation of galaxies is the radiation of the billions of stars that comprise them, more or less similar to the Sun. Careful study of the spectra of galaxies many years ago led to a discovery of fundamental importance. The fact is that by the nature of the shift in the wavelength of any spectral line in relation to the laboratory standard, one can determine the speed of movement of the emitting source along the line of sight. In other words, it is possible to determine at what speed the source is approaching or moving away.
If the light source approaches, the spectral lines shift towards shorter wavelengths; if it moves away, towards longer ones. This phenomenon is called the Doppler effect. It turned out that galaxies (with the exception of a few that are closest to us) have spectral lines always shifted to the long-wavelength part of the spectrum (red shift of the lines), and the magnitude of this shift is greater, the further away the galaxy is from us.
This means that all galaxies are moving away from us, and the speed of expansion increases as the galaxies move away. It reaches enormous values. For example, the recession speed of the radio galaxy Cygnus A, found from the red shift, is close to 17 thousand km/s. Twenty-five years ago, the record belonged to the very faint (in optical rays of the 20th magnitude) radio galaxy 3S 295. In 1960, its spectrum was obtained. It turned out that the well-known ultraviolet spectral line belonging to ionized oxygen is shifted to the orange region of the spectrum! From here it is easy to find that the speed of removal of this amazing star system is 138 thousand km/s, or almost half the speed of light! Radio galaxy 3S 295 is distant from us at a distance that light travels in 5 billion years. Thus, astronomers studied the light that was emitted when the Sun and planets were formed, and maybe even a little earlier... Since then, even more distant objects have been discovered (Chapter 6).
We will not touch upon the reasons for the expansion of a system consisting of a huge number of galaxies here. This complex question is the subject of modern cosmology. However, the very fact of the expansion of the Universe is of great importance for analyzing the development of life in it (Chapter 7).
Superimposed on the overall expansion of the galaxy system are the erratic velocities of individual galaxies, typically several hundred kilometers per second. This is why the galaxies closest to us do not exhibit a systematic redshift. After all, the speeds of random (so-called peculiar) movements for these galaxies are greater than the regular redshift speed. The latter increases as the galaxies move away by approximately 50 km/s, for every million parsecs. Therefore, for galaxies whose distances do not exceed several million parsecs, the random velocities exceed the receding velocity due to the redshift. Among nearby galaxies, there are also those that are approaching us (for example, the Andromeda nebula M 31).
Galaxies are not uniformly distributed in metagalactic space, i.e. with constant density. They show a pronounced tendency to form separate groups or clusters. In particular, a group of about 20 galaxies close to us (including our Galaxy) forms the so-called local system. In turn, the local system is part of a large cluster of galaxies, the center of which is in that part of the sky on which the Virgo constellation is projected. This cluster has several thousand members and is among the largest. In Fig. Figure 8 shows a photograph of the famous galaxy cluster in the constellation Corona Borealis, numbering hundreds of galaxies. In the space between clusters, the density of galaxies is tens of times less than inside the clusters.
Noteworthy is the difference between clusters of stars that form galaxies and clusters of galaxies. In the first case, the distances between cluster members are enormous compared to the sizes of the stars, while the average distances between galaxies in galaxy clusters are only several times larger than the sizes of the galaxies. On the other hand, the number of galaxies in clusters cannot be compared with the number of stars in galaxies. If we consider a collection of galaxies as a kind of gas, where the role of molecules is played by individual galaxies, then we must consider this medium to be extremely viscous.
Incredible facts
Have you ever wondered how big the Universe is?
8. However, this is nothing compared to the Sun.
Photo of the Earth from space
9. And this view of our planet from the moon.
10. This is us from the surface of Mars.
11. And this view of the Earth behind the rings of Saturn.
12. And this is the famous photograph" Pale blue dot", where the Earth is photographed from Neptune, from a distance of almost 6 billion kilometers.
13. Here is the size Earth compared to the Sun, which doesn’t even fit completely into the photo.
Biggest star
14. And this Sun from the surface of Mars.
15. As the famous astronomer Carl Sagan once said, in space more stars than grains of sand on all the beaches of the Earth.
16. There are many stars that are much larger than our Sun. Just look how tiny the Sun is.
Photo of the Milky Way galaxy
18. But nothing can compare to the size of the galaxy. If you reduce The sun to the size of a leukocyte(white blood cell), and shrink the Milky Way Galaxy using the same scale, the Milky Way would be the size of the United States.
19. This is because the Milky Way is simply huge. That's where the solar system is inside it.
20. But we see only very much a small part of our galaxy.
21. But even our galaxy is tiny compared to others. Here Milky Way compared to galaxy IC 1011, which is located 350 million light years from Earth.
22. Think about it, in this photograph taken by the Hubble telescope, thousands of galaxies, each containing millions of stars, each with their own planets.
23. Here is one of galaxy UDF 423, located 10 billion light years away. When you look at this photograph, you are looking billions of years into the past. Some of these galaxies formed several hundred million years after the Big Bang.
24. But remember that this photo is very, a very small part of the universe. It's just an insignificant part of the night sky.
25. We can quite confidently assume that somewhere there is black holes. Here's the size of the black hole compared to Earth's orbit.
Which are on it. For the most part, we are all chained to the place where we live and work. The size of our world is amazing, but it is absolutely nothing compared to the Universe. As the saying goes - "born too late to explore the world, and too early to explore space". It's even insulting. However, let's get started - just be careful not to get dizzy.
1. This is Earth.
This is the same planet that this moment is the only home for humanity. The place where life magically appeared (or maybe not so magically) and in the course of evolution you and I appeared.
2. Our place in the solar system.
The closest large space objects that surround us, of course, are our neighbors in the solar system. Everyone remembers their names from childhood, and during lessons about the world around them they make models. It so happened that even among them we are not the biggest...
3. The distance between our Earth and the Moon.
It doesn't seem that far, right? And if we also take into account modern speeds, then it’s “nothing at all.”
4. In fact, it’s quite far away.
If you try, then very accurately and comfortably - between the planet and the satellite you can easily place the rest of the planets of the solar system.
5. However, let's continue talking about planets.
In front of you North America, as if it were placed on Jupiter. Yes, this small green speck is North America. Can you imagine how huge our Earth would be if we moved it to the scale of Jupiter? People would probably still be discovering new lands)
6. This is Earth compared to Jupiter.
Well, more precisely six Earths - for clarity.
7. Rings of Saturn, sir.
The rings of Saturn would have such a gorgeous appearance, provided they revolved around the Earth. Look at Polynesia - a bit like the Opera icon, right?
8. Let's compare the Earth with the Sun?
It doesn't look that big in the sky...
9. This is the view of the Earth when looking at it from the Moon.
Beautiful, right? So lonely against the backdrop of empty space. Or not empty? Let's continue...
10. And so from Mars
I bet you wouldn't even be able to tell if it was Earth.
11. This is a shot of Earth just beyond the rings of Saturn
12. But beyond Neptune.
A total of 4.5 billion kilometers. How long would it take to search?
13. So, let's go back to the star called the Sun.
A breathtaking sight, isn't it?
14. Here is the Sun from the surface of Mars.
15. And here is its comparison with the Scale of the star VY Canis Majoris.
How do you like it? More than impressive. Can you imagine the energy concentrated there?
16. But this is all bullshit, if you compare ours native star the size of the Milky Way galaxy.
To make it more clear, imagine that we have compressed our Sun to the size of a white blood cell. In this case, the size of the Milky Way is quite comparable to the size of Russia, for example. This is the Milky Way.
17. In general, stars are huge
Everything that is placed in this yellow circle is everything that you can see at night from Earth. The rest is inaccessible to the naked eye.
18. But there are other galaxies.
Here is the Milky Way compared to the galaxy IC 1011, which is located 350 million light years from Earth.
Let's go over it again?
So, this Earth is our home.
Let's zoom out to the size of the solar system...
Let's zoom out a little more...
And now to the size of the Milky Way...
Let's continue to reduce...
And further…
Almost ready, don't worry...
Ready! Finish!
This is all that humanity can now observe using modern technology. It’s not even an ant... Judge for yourself, just don’t go crazy...
Such scales are hard to even comprehend. But someone confidently declares that we are alone in the Universe, although they themselves are not really sure whether the Americans were on the Moon or not.
Hang in there guys... hang in there.
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