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Use online interactive scale of the universe: real dimensions of the Universe, comparison of space objects, planets, stars, clusters, galaxies.

We all think of dimensions in general terms, such as another reality, or our perception of the environment around us. However, this is only part of what measurements really are. And, above all, the existing understanding measurements of the scales of the universe is the best of what is described in physics.

Physicists assume that measurements are simply different facets of the perception of the scale of the universe. For example, the first four dimensions include length, width, height, and time. However, according to quantum physics, there are other dimensions that describe the nature of the universe and possibly all universes. Many scientists believe that there are currently about 10 dimensions.

Interactive Scale of the Universe

Measuring the scale of the universe

The first dimension, as already mentioned, is the length. A good example of a one-dimensional object is a straight line. This line only has a length dimension. The second dimension is the width. This dimension also includes length, a good example of a two-dimensional object would be an impossibly thin plane. Things in two dimensions can only be seen in cross section.

The third dimension includes height, and this is the dimension we are most familiar with. Combined with length and width, this is the most visible part of the universe in terms of dimensions. The best physical form to describe this dimension is a cube. The third dimension exists when length, width and height intersect.

Now things get a little more complicated, because the remaining 7 dimensions are associated with non-material concepts that we cannot directly observe, but we know that they exist. The fourth dimension is time. It is the difference between past, present and future. Thus, the best description of the fourth dimension would be chronology.

Other dimensions deal with probabilities. The fifth and sixth dimensions are related to the future. According to quantum physics, there can be any number of possible futures, but there is only one outcome, and the reason for this is choice. The fifth and sixth dimensions are associated with the bifurcation (change, branching) of each of these probabilities. In essence, if you could control the fifth and sixth dimensions, you could go back in time or visit various futures.

Dimensions 7 to 10 are related to the universe and its scale. They are based on the fact that there are several universes, and each has its own sequence of measurements of reality and possible outcomes. The tenth and final dimension is actually one of all possible outcomes of all universes.

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Neighborhood with a black hole is not the safest option for any space object. After all, these mysterious formations are so...

If you get out of the solar system, then find yourself among stellar neighbors living their own lives. But which star is closest? ...

which are on it. In the bulk, 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 they say - "born too late to explore the world and too early to explore space". It's even embarrassing. However, let's get started - just look so that your head does not spin.

1. This is the Earth.

This is the same planet that is currently the only home for humanity. The place where life magically appeared (or maybe not so magically) and where we appeared in the course of evolution.

2. Our place in the solar system.

The nearest large space objects that surround us, of course, are our neighbors in the solar system. Everyone remembers their names from childhood, and at the lessons of the world around them they sculpt 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, does it? And if we take into account modern speeds, then there is nothing at all.

4. In fact - far enough.

If you try, it is very accurate and comfortable - 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 the planets.

Before you is 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 discover new lands)

6. This is Earth compared to Jupiter.

Nuuu, or rather six Earths - for clarity.

7. Rings of Saturn, sir.

The rings of Saturn would have such a gorgeous view, with the condition that they revolve around the Earth. Look at Polynesia - looks a bit like an Opera icon, right?

8. Compare the Earth with the Sun?

It doesn't look that big in the sky...

9. This view opens up to the Earth, if you look at it from the moon.

It's 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 know if it's Earth.

11. This is a picture of the Earth just outside the rings of Saturn

12. But behind Neptune.

Only 4.5 billion kilometers. How long would you search?

13. So, let's go back to the star called the Sun.

An exciting sight, isn't it?

14. Here is the Sun from the surface of Mars.

15. And here is its comparison with the Scales of the star VY Canis Major.

How are you? More than impressive. Can you imagine what kind of energy is concentrated there?

16. But this is all garbage, if we compare our native star with the size of the Milky Way galaxy.

To make it clearer, 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, the stars are huge

Everything that is placed in this yellow circle is everything that you can see at night from Earth. The rest is not visible to the naked eye.

18. But there are also other galaxies.

Here is the Milky Way compared to the galaxy IC 1011, located 350 million light years from Earth.

Let's go one more time, shall we?

So this is Earth, our home.

Let's zoom out to the size of the solar system...

Let's take a little more...

And now to the size of the Milky Way ...

Let's keep decreasing...

And further…

Almost done, don't worry...

Ready! The 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 do not even fit in the head. But someone declares with confidence that we are alone in the universe, although they themselves are not really sure whether the Americans were on the moon or not.

Hold on guys... hold on.

If professional astronomers constantly and tangibly imagined the monstrous magnitude of cosmic distances and time intervals in the evolution of celestial bodies, they could hardly successfully develop the science to which they devoted their lives. The spatio-temporal scales familiar to us from childhood are so insignificant compared to the cosmic scales that when it comes to consciousness, it literally takes your breath away. Dealing with some problem of 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 methods of observation, or builds in his imagination, consciously or unconsciously, some small model investigated space system. In this case, a correct understanding of the relative dimensions of the system under study (for example, the ratio of the dimensions of the details of a given space system, the ratio of the dimensions of this system and others similar or unlike it, etc.) and time intervals (for example, the ratio of the flow velocity of a given process to the rate of some other).

One of the authors of this article has done quite a lot of work, for example, on the solar corona and the Galaxy. And they always seemed to him of irregular shape as spheroidal bodies of approximately the same size - something about 10 cm ... Why 10 cm? This image arose subconsciously, simply because too often, thinking about this or that issue of solar or galactic physics, the author drew in an ordinary notebook (in a box) the outlines of the subjects of his thoughts. He drew, trying to adhere to the scale of phenomena. On one very curious 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 one. But he quietly forgot about it. And if, in a number of cases, the large dimensions of the galactic corona acquired some fundamental significance (it did happen), this was taken into account formally and mathematically. And all the same, visually both "crowns" seemed equally small ...

If the author, in the process of this work, indulged in philosophical reflections on the enormity of the size of the Galaxy, on the unimaginable rarefaction of the gas that makes up the galactic crown, on the insignificance of our little planet and our own existence, and on other other equally correct subjects, work on the problems of the solar and galactic Corona would stop automatically...

Let the reader forgive me this "lyrical digression". I have no doubt that other astronomers had the same thoughts when they worked on their problems. It seems to me that sometimes it is useful to get acquainted with the "kitchen" of scientific work...

Until relatively recently, the globe seemed huge to man. It took the brave companions of Magellan over three years to make the first round-the-world trip almost half a thousand years ago at the cost of incredible hardships. A little over 100 years have passed since the time when the resourceful hero of a science fiction novel by Jules Verne made, using the latest technological advances of that time, a journey around the world in 80 days. And just a little less than 50 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 the thoughts of people 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 at this angle, a one-kopeck coin is visible from a distance of 3 km.

None of the stars - the nearest neighbors of the solar system - is closer to us than 1 pc. For example, the mentioned Proxima Centauri is removed from us at a distance of about 1.3 pc. On the scale at which we depicted the solar system, this corresponds to 2 thousand km. All this well illustrates the great isolation of our solar system from the surrounding star systems, some of these systems may have many similarities with it.

But the stars surrounding the Sun and the Sun itself constitute only a negligible part of the gigantic collective of stars and nebulae, which is called the "Galaxy". We see this cluster of stars on clear moonless nights as a strip 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 that make up it fill a volume that has the shape of a highly compressed ellipsoid of revolution. Often in popular literature the shape of the Galaxy is compared to a biconvex lens. In fact, everything is much more complicated, and the picture drawn is too rough. In fact, it turns out that different types of stars are concentrated to the center of the Galaxy and to its "equatorial plane" in completely different ways. 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 intermediate cases. Nevertheless, it turns out that the main part of the stars in the Galaxy is located in a giant disk, the diameter of which is about 100 thousand light years, and the thickness is about 1500 light years. In this disk, there are slightly more than 150 billion stars of various types. Our Sun is one of these stars, located on the periphery of the Galaxy near 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 nucleus of the Galaxy (or its center) is about 30 thousand light years. The 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 greater than the average stellar density in the vicinity of the Sun. In addition, stars tend to form separate groups or clusters. A good example of such a cluster is the Pleiades, which are visible in our winter skies.

The Galaxy also contains structural details on a much larger scale. Studies have shown that nebulae, as well as hot massive stars, are distributed along the branches of the spiral. The spiral structure is especially well seen in other star systems - galaxies (with a small letter, in contrast to our star system - the Galaxy). Establishing the spiral structure of the Galaxy in which we ourselves find ourselves has proved extremely difficult.

The stars and nebulae within the Galaxy move in a rather complex way. 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 regions of the Galaxy have different periods of rotation. Thus, the Sun and the stars surrounding it in a huge area of several hundred light-years in size make a complete revolution in about 200 million years. Since the Sun, together with the family of planets, has apparently existed for about 5 billion years, during its evolution (from its birth from a gaseous nebula to its current state) it has made about 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 - a blooming age...

The speed of the movement of the Sun and its neighboring stars along their almost circular galactic orbits reaches 250 km/s. This regular movement around the galactic core is superimposed by the chaotic, erratic movements of the stars. The velocities of such movements are much lower - about 10-50 km/s, and they are different for objects of different types. Hot massive stars have the least speed (6-8 km/s), solar-type stars have about 20 km/s. The lower these velocities, the more "flat" is the distribution of this type of stars.

On the scale that we used to visualize the solar system, the dimensions of the Galaxy would be 60 million km - a value that is already quite close to the distance from the Earth to the Sun. From this it is clear that as one penetrates into more and more remote regions of the Universe, this scale is no longer suitable, since it loses visibility. 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. 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 - 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 is a unit of length equal to 10 -8 cm).

We have already emphasized that the stars are separated from each other by great distances, and thus practically isolated. In particular, this means that the stars almost never collide with each other, although the movement of each of them is determined by the gravitational force field created by all the stars in the Galaxy. If we consider the Galaxy as a certain region filled with gas, with stars playing the role of gaseous molecules and atoms, then we must consider this gas to be extremely rarefied. In the vicinity of the Sun, the average distance between stars is about 10 million times greater than the average diameter of the stars. Meanwhile, under normal conditions in ordinary air, the average distance between molecules is only a few tens of times greater than the dimensions 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 the stellar density is relatively high, collisions between stars will occur from time to time. Here, approximately one collision should be expected every million years, while in the "normal" regions of the Galaxy during the entire history of the evolution of our star system, which is at least 10 billion years, there were practically no collisions between stars.

For several decades, astronomers have been persistently studying other star systems that are more or less similar to ours. This area of research has been called "extragalactic astronomy". It now plays almost a leading role in astronomy. Over the past three decades, extragalactic astronomy has made astonishing progress. Gradually, the grandiose contours of the Metagalaxy began to emerge, in which our star system is included as a small particle. We still do not 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 deep theoretical research. Yet the overall structure of the Metagalaxy has largely become clear in recent years.

We can define the Metagalaxy as a collection of star systems - galaxies moving in the vast expanses of the part of the Universe that 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 with the total length of our Galaxy. Another galaxy "close" to us is a nebula in the constellation Andromeda. It is visible to the naked eye as a faint spot of light of the 5th magnitude.

In fact, this is a huge stellar world, in terms of the number of stars and the total mass of three times the size of 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 under No. 31), is about 1800 thousand light years, which is about 20 times the size of the Galaxy. The M 31 nebula has a pronounced 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 denoted by the symbols Sa, Sb and Sc, depending on the nature of the development of the spiral structure; in the presence of a “bar” passing through the core, the letter B is placed after the letter S) there are spheroidal and ellipsoidal, devoid of any traces of the spiral structure, as well as "wrong" galaxies, a good example of which is the Magellanic Clouds.

Large telescopes observe a huge number of galaxies. If there are about 250 galaxies brighter than the visible 12th magnitude, then there are already about 50 thousand brighter than the 16th magnitude. The faintest objects that a reflecting telescope with a mirror diameter of 5 m can photograph at the limit have a 24.5th magnitude, for orbiting telescope "Hubble" this limit - objects of 30 magnitude. It turns out that among the billions of such weakest objects, the majority are galaxies. Many of them are distant from us at distances that light travels in 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!

The spectra of most galaxies resemble the sun; in both cases, separate dark absorption lines are observed against a rather bright background. There is nothing unexpected in this, since the radiation of galaxies is the radiation of billions of their constituent stars, more or less similar to the Sun. Careful study of the spectra of galaxies many years ago led to one discovery of fundamental importance. The fact is that by the nature of the shift of the wavelength of any spectral line with respect to the laboratory standard, one can determine the speed of the radiating source along the line of sight. In other words, it is possible to establish with what speed the source is approaching or receding.

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 in galaxies (with the exception of a few closest to us) the spectral lines are always shifted to the long-wavelength part of the spectrum (the "redshift" of the lines), and the magnitude of this shift is the greater, the further 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 receding velocity of the Cygnus A radio galaxy found from the redshift is close to 17,000 km/s. For a long time, the record belonged to the very weak (in optical rays of magnitude 20) radio galaxy ZC 295. In 1960, its spectrum was obtained. It turned out that the 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! The radio galaxy 3C 295 is at a distance from us that light travels in 5 billion years. Thus, astronomers have studied the light that was emitted when the Sun and planets formed, and maybe even "a little" earlier ... Since then, much more distant objects have been discovered.

Superimposed on the general expansion of the system of galaxies are the erratic speeds of individual galaxies, usually equal to several hundred kilometers per second. That is why the galaxies closest to us do not exhibit a systematic redshift. After all, the velocities of random (so-called "peculiar") motions for these galaxies are greater than the regular redshift velocity. The latter increases as the galaxies move away by about 50 km/s, for every million parsecs. Therefore, for galaxies whose distances do not exceed a few 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 the 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 included in a large cluster of galaxies, the center of which is located in that part of the sky on which the constellation Virgo is projected. This cluster has several thousand members and is one of the largest. In the space between clusters, the density of galaxies is ten times less than inside clusters.

Attention is drawn to the difference between clusters of stars that form galaxies and clusters of galaxies. In the first case, the distances between cluster members are huge compared to the sizes of stars, while the average distances between galaxies in galaxy clusters are only several times greater than the sizes of galaxies. On the other hand, the number of galaxies in clusters cannot be compared with the number of stars in galaxies. If we consider the totality 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 the Bohr atom? On this scale, the distance to the Andromeda nebula will be somewhat more than 6 m, the distance to the central part of the Virgo galaxy cluster, which includes our local system of galaxies, 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 3C 295 will reach 25 km ...

We got acquainted in the most general form with the main structural features and with the scales of the Universe. It is like a frozen frame of its development. It has not always been the way we see it now. Everything in the Universe changes: stars and nebulae appear, develop and "die", the Galaxy develops in a natural way, the very structure and scales of the Metagalaxy change.

Stairway to infinity

How to determine the distance to the stars? How do you know that Alpha Centauri is about 4 light years away? Indeed, by the brightness of a star, as such, you can hardly determine anything - the brilliance of a dim close and bright distant stars can be the same. And yet there are many fairly reliable ways to determine the distance from the Earth to the farthest corners of the universe. Astrometric satellite "Hipparchus" for 4 years of work determined the distances to 118 thousand SPL stars

Whatever physicists say about the three-dimensionality, six-dimensionality or even eleven-dimensionality of space, for the astronomer the observable Universe is always two-dimensional. What is happening in the Cosmos is seen by us as a projection onto the celestial sphere, just as in a movie the whole complexity of life is projected onto a flat screen. On the screen, we can easily distinguish the far from the near thanks to 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. How can one distinguish a nearby dim star from a distant but bright quasar without them? Only knowing the distance to an object, one can evaluate its energy, and from here a direct road 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 come to Earth about once a day from various directions. Initial estimates of their remoteness ranged from hundreds of astronomical units (tens of light hours) to hundreds of millions of light years. Accordingly, the scatter in the models was also impressive - from the annihilation of comets from antimatter 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 different explanations for the nature of gamma-ray bursts had been proposed. Now, when we were able to estimate the distances to their sources, there are only two models left.

But how to measure the distance if neither the ruler nor the locator beam can reach the object? The triangulation method, which is widely used in ordinary terrestrial geodesy, comes to the rescue. We select a segment of known length - the base, measure from its ends the angles under which a point is visible inaccessible for one reason or another, and then simple trigonometric formulas give the required distance. When we move from one end of the base to the other, the apparent direction to the point changes, it shifts against the background of distant objects. This is called parallax shift, or parallax. Its value is the smaller, the farther the object is, and the larger, the longer the base.

To measure the distances to the 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) came to be called the annual parallax. Tycho Brahe tried to measure it, who did not like the Copernican idea about the rotation of the Earth around the Sun, and he decided to check it - after all, parallaxes also prove the orbital motion of the Earth. The measurements carried out had an accuracy that was impressive for the 16th century - about one minute of arc, but this was completely insufficient for measuring parallaxes, which Brahe himself had no idea about 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, the future director of the Greenwich Observatory. At first, it seemed that luck smiled at him: the star Gamma Draco, chosen for observations, indeed fluctuated around its average position with a span of 20 seconds of arc during the year. However, the direction of this shift was different from that 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. Similarly, raindrops leave sloping paths on the windows of a bus. This phenomenon, called annual aberration, was the first direct evidence of the Earth moving around the Sun, but had nothing to do with parallaxes.

Only a century later, the accuracy of goniometric instruments reached the required level. In the late 30s of the XIX century, in the words of John Herschel, "the wall that prevented penetration into the stellar Universe was broken almost simultaneously in three places." In 1837, Vasily Yakovlevich Struve (at that time the director of the Derpt Observatory, and later of the Pulkovo Observatory) published the parallax of Vega measured by him - 0.12 arc seconds. The following year, Friedrich Wilhelm Bessel reported that the parallax of the star of the 61st Cygni is 0.3". And a year later, the Scottish astronomer Thomas Henderson, who worked in the Southern Hemisphere at the Cape of Good Hope, measured the parallax in the Alpha Centauri system - 1.16 " . True, later it 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 second of arc.

For distances measured by the parallactic method, a special unit of length was introduced - 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, one must 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 270,000 astronomical units. A thousand parsecs is called a kiloparsec (kpc), a million parsecs is called a megaparsec (Mpc), and a billion is called a gigaparsec (Gpc).

The measurement of extremely small angles required technical sophistication and great diligence (Bessel, for example, processed more than 400 individual observations of Cygnus 61), but after the first breakthrough, things got easier. By 1890, the parallaxes of already three dozen stars had been measured, and when photography began to be widely used in astronomy, the accurate measurement of parallaxes was completely put on stream. Parallax measurements are the only method for directly determining the distances to individual stars. However, during ground-based observations, atmospheric interference does not allow the parallax method to measure distances above 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 published more and more often. Their radiation falls on 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 masers with the rotation speed of this star system. A year later, Ye Xu (China) and colleagues applied the classical parallax method to "local" maser sources to measure the distance (2 kpc) to one of the spiral arms of our Galaxy. Perhaps, in 1999, J. Hernstin (USA) and colleagues managed to advance the farthest. Tracking the movement of masers in the accretion disk around the black hole at the core of the active galaxy NGC 4258, astronomers have determined that this system is 7.2 Mpc away from us. To date, this is an absolute record of geometric methods.

Astronomers standard candles

The farther away from us is the source of radiation, the dimmer it is. If you know the true luminosity of an object, then by comparing it with the visible brightness, you can find the distance. Probably the first to apply this idea to the measurement of distances to stars was Huygens. At night, he observed Sirius, and during the day he compared its brilliance to 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 from photographic plates. Particular attention was paid to variable stars, whose brightness 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 of 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 Levitt Cepheids were in the same star system - the Small Magellanic Cloud - it could be considered that they were removed from us at the same (albeit unknown) distance. 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 by a geometric method in order to calibrate the entire dependence and to be able, by measuring the period, to determine the true luminosity of any Cepheid, and from it the distance to the star and the star system containing it.

But, unfortunately, there are no Cepheids in the vicinity of the Earth. The nearest of them, the Polar Star, is, as we now know, 130 pc from the Sun, that is, it is beyond the reach of ground-based parallax measurements. This did not allow to throw a bridge directly from parallaxes to Cepheids, and astronomers had to build a structure, which is now figuratively called the distance ladder.

An intermediate step on it was open star clusters, including from several tens to hundreds of stars, connected by a common time and place of birth. If you plot the temperature and luminosity of all the stars in the cluster, most of the points will fall on one inclined line (more precisely, a strip), which is called the main sequence. The temperature is determined with high accuracy from the spectrum of the star, and the luminosity is determined from the apparent brightness and distance. If the distance is unknown, the fact again comes to the rescue that all the stars in the cluster are almost the same distance from us, so that within the cluster, the 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 due only to the fact that they are at different distances. If we determine the distance to one of the clusters by a geometric method, then we will find out what the “real” main sequence looks like, and then, by comparing data from other clusters with it, we will determine the distances to them. This technique is called "main sequence fitting". For a long time, the Pleiades and Hyades served as a standard for it, the distances to which were determined by the method of group parallaxes.

Fortunately for astrophysics, Cepheids have been found in about two dozen open clusters. Therefore, by measuring the distances to these clusters by fitting the main sequence, one can "reach the ladder" to the Cepheids, which are on its third step.

As an indicator of distances, Cepheids are very convenient: 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 high-profile epithets, such as "beacons of the universe" or "mileposts of astrophysics." The Cepheid "ruler" stretches up to 20 Mpc - this is about a hundred times the size of our Galaxy. Further, they can no longer be distinguished even with the most powerful modern instruments, and in order to climb the fourth rung of the distance ladder, you need something brighter.

METHODS FOR MEASURING SPACE DISTANCES

To the ends of the universe

One of the most powerful extragalactic methods for measuring distances is based on a pattern known as the Tully-Fisher relation: the brighter a spiral galaxy, the faster it rotates. When a galaxy is viewed edge-on or at a significant inclination, half of its matter is moving towards us due to rotation, and half is receding, which leads to broadening of the spectral lines due to the Doppler effect. This expansion determines the speed of rotation, according to it - the luminosity, and then from a comparison with the apparent brightness - the distance to the galaxy. And, of course, to calibrate this method, galaxies are needed, the distances to which have already been measured using Cepheids. The Tully-Fisher method is very long-range and covers galaxies that are hundreds of megaparsecs away from us, but it also has a limit, since it is not possible to obtain enough high-quality spectra for too distant and faint galaxies.

In a somewhat larger range of distances, another “standard candle” operates - type Ia supernovae. Flashes of such supernovae are "same type" thermonuclear explosions of white dwarfs with a mass slightly higher than the critical one (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 from us, but you never know the distance to which galaxy you can measure, because it is not known in advance exactly where the next supernova will break out.

So far, only one method allows moving even further - redshifts. Its history, like the history of Cepheids, begins simultaneously with the 20th century. In 1915, the American Westo Slifer, studying the spectra of galaxies, noticed that in most of them the lines are redshifted relative to the "laboratory" position. In 1924, the German Karl Wirtz noticed that this shift is the stronger, the smaller the angular size of the galaxy. However, only Edwin Hubble in 1929 managed to bring these data into a single picture. According to the Doppler effect, the redshift of the lines in the spectrum means that the object is moving away from us. Comparing the spectra of galaxies with the distances to them, determined by the Cepheids, Hubble formulated the law: the speed of the removal of a galaxy is proportional to the distance to it. The coefficient of proportionality in this ratio is called the Hubble constant.

Thus, the expansion of the Universe was discovered, and with it the possibility of determining the distances to galaxies from their spectra, of course, provided that the Hubble constant is tied to some other “rulers”. Hubble himself performed this binding 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” ratios. The calibration was performed anew based on "classical" Cepheids, and only then did the value of the Hubble constant become close to modern estimates: 50–100 km/s for every megaparsec of distance to the galaxy.

Now, redshifts are used to determine distances to galaxies that are 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 time of its reception on Earth, or the distance traveled by light on the way from the starting point to the end point. Therefore, astronomers prefer to indicate for distant objects only the directly observed redshift value, without converting it to megaparsecs.

Redshifts are currently the only method for estimating "cosmological" distances comparable to the "size of the Universe", and at the same time, this is perhaps the most widespread technique. In July 2007, a catalog of redshifts of 77,418,767 galaxies was published. However, when creating it, a somewhat simplified automatic technique for analyzing spectra was used, and therefore errors could creep into some values.

Team play

Geometric methods for measuring distances are not limited to 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 motion of the Sun and stars relative to each other. 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 to one point - the radiant. Its position indicates the angle at which the cluster flies to the line of sight. Knowing this angle, one can decompose the motion of the stars in the cluster 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 by the Doppler effect and, taking into account the proportion found, the projection of the velocity onto the sky is calculated - also in kilometers per second. It remains to compare these linear velocities of the stars with the angular velocities 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

Building our ladder 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 reference 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 determine the remoteness of the Sun was Aristarchus of Samos, who proposed the heliocentric system of the world one and a half thousand years before Copernicus. It turned out that the Sun is 20 times farther from us than the Moon. This estimate, as we now know, 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 all other astronomers followed him) 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 stars simultaneously from Paris (Cassini) and Cayenne (Richet). The distance from France to French Guiana served as the base of the parallactic triangle, from which they determined the distance to Mars, and then calculated the astronomical unit from the equations of celestial mechanics, deriving a value of 140 million kilometers.

Over the next two centuries, the transits of Venus across the solar disk became the main tool for determining the scale of the solar system. By observing them simultaneously from different parts of the globe, it is possible to calculate the distance from the Earth to Venus, and hence all other distances in the solar system. In the XVIII-XIX centuries, this phenomenon was observed four times: in 1761, 1769, 1874 and 1882. These observations became one of 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 at the end of the 18th 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 have already taken an active part in the research. Unfortunately, the extreme complexity of observations has led to considerable discrepancy in the estimates of the astronomical unit - from about 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 the knowledge of the length of the base, in the role of which, when measuring the astronomical unit, the radius of the Earth acted. So in the end, the foundation of the ladder of cosmic distances was laid by surveyors.

Only in the second half of the 20th century did fundamentally new methods for determining cosmic distances appear at the disposal of scientists - laser and radar. They made it possible to increase the accuracy of measurements in the solar system hundreds of thousands of times. The error of radar for Mars and Venus is several meters, and the distance to the corner reflectors installed on the Moon is measured to within centimeters. The currently accepted value of the astronomical unit is 149,597,870,691 meters.

The difficult fate of "Hipparchus"

Such a radical progress in the measurement of the astronomical unit raised the question of the distances to stars in a new way. The accuracy of determining parallaxes is limited by the Earth's atmosphere. Therefore, back in the 1960s, the idea arose to bring a goniometric instrument into space. It was realized in 1989 with the launch of the European astrometric satellite Hipparchus. This name is a well-established, although formally not quite correct translation of the 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 directory.

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 out” to 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 the 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 trouble. Due to a failure in the upper stage, the Hipparchus did not enter the calculated geostationary orbit and remained on an intermediate highly elongated trajectory. The specialists of the European Space Agency nevertheless managed to cope with the situation, and the orbital astrometric telescope successfully operated for 4 years. The processing of results lasted the same amount of time, and in 1997 a stellar catalog was published with parallaxes and proper motions of 118,218 luminaries, including about two hundred Cepheids.

Unfortunately, in a number of issues the desired clarity has not yet come. The result for the Pleiades turned out to be the most incomprehensible - 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, getting a value of only 118 parsecs. Acceptance of the new value would require adjustments to both the theory of stellar evolution and the scale of intergalactic distances. This would be a serious problem for astrophysics, and the distance to the Pleiades began to be carefully checked. By 2004, several groups had independently obtained estimates of the distance to the cluster in the range from 132 to 139 pc. Offensive voices began to be heard with suggestions that the consequences of putting the satellite into the wrong orbit still could not be completely eliminated. Thus, in general, all parallaxes measured by him were called into question.

The Hipparchus team was forced to admit that the measurements were generally accurate, but might need to be re-processed. The point is that parallaxes are not measured directly in space astrometry. Instead, Hipparchus measured the angles between numerous pairs of stars over and over again for four years. These angles change both due to the parallactic displacement and due to the proper motions of the stars in space. To "pull out" exactly the values of parallaxes from observations, a rather complicated 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 of an improvement this has made.

But the problems of Hipparchus do not end there. The Cepheid parallaxes determined by him turned out to be insufficiently accurate for a confident calibration of the "period-luminosity" ratio. Thus, the satellite failed to solve the second task facing it. Therefore, several new projects of space astrometry are currently being considered in the world. The European Gaia project, which is scheduled to launch in 2012, is the closest to implementation. Its principle of operation is the same as that of the Hipparchus - repeated measurements of the angles between pairs of stars. However, thanks to powerful optics, it will be able to observe much dimmer objects, and the use of the interferometry method will increase the accuracy of angle measurements to tens of microseconds of arc. 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 work. Thus, a three-dimensional map of a significant part of the Galaxy will be constructed.

Aristotle's universe ended at nine distances from the Earth to the Sun. Copernicus believed that the stars were 1,000 times further away than the sun. Parallaxes pushed even the nearest stars away by light years. At the very beginning of the 20th century, the 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 final are they?

Of course, each rung of the distance ladder has its own, larger or smaller errors, but in general, the scales of the Universe are well defined, verified by various methods that are independent of each other, and add up to a single consistent picture. So the current 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 Wiebe. Earth (Sol III).

Based on materials: www.vokrugsveta.ru, galspace.spb.ru,Shklovsky I.S. "Universe, life, mind" / Ed. N.S. Kardashev and V.I. Moroza. - 6th ed.

The scale of the universe and its structure

The author of this book has done a lot of work, for example, on the solar corona and the Galaxy. And they always seemed to him of irregular shape, spheroidal bodies of approximately the same size - something about 10 cm ... Why 10 cm? This image arose subconsciously, simply because too often, thinking about this or that issue of solar or galactic physics, the author drew in an ordinary notebook (in a box) the outlines of the subjects of his thoughts. He drew, trying to adhere to the scale of phenomena. On one very curious 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 one. But he quietly forgot about it. And if, in a number of cases, the large dimensions of the galactic corona acquired some fundamental significance (it did happen), this was taken into account formally and mathematically. And all the same, visually both crowns seemed equally small ...

Let the reader forgive me this lyrical digression. I have no doubt that other astronomers had the same thoughts when they worked on their problems. It seems to me that sometimes it is useful to get to know the kitchen of scientific work better ...

If we want to discuss the exciting questions about the possibility of intelligent life in the Universe on the pages of this book, then, first of all, it will be necessary to form a correct idea of its space-time scales. Until relatively recently, the globe seemed huge to man. It took the brave companions of Magellan over three years to make the first round-the-world trip 465 years ago at the cost of incredible hardships. A little over 100 years have passed since the time when the resourceful hero of a science fiction novel by Jules Verne made, using the latest technological advances of that time, a journey 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 in 89 minutes on the legendary Vostok spacecraft. And the thoughts of people 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 most distant planet in the solar system, is 40 times the average distance from the Earth to the Sun. It is currently unknown whether there are planets in the solar system even more distant from the Sun than Pluto. It can only be argued that if such planets exist, they are relatively small. Conventionally, the size of the solar system can be taken equal to 50-100 astronomical units *, or about 10 billion km.

On our earthly scale, this is a very large value, about 1 million larger than the diameter of the Earth.

We can more visually represent the relative scales of the solar system as follows. Let the Sun be represented by a billiard ball with a diameter of 7 cm. Then the closest planet to the Sun - Mercury is at a distance of 280 cm from it on this scale. in many ways, the still mysterious Pluto is about 300m away. 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 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 with him, interplanetary distances within the solar system seem to be mere trifles. Readers, of course, know that such a unit of length as a kilometer is never used to measure interstellar distances**).

This unit of measurement (as well as 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 science, to estimate interstellar and intergalactic distances, the light year is used as a unit of measurement. 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 9.46 x 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;

But the stars surrounding the Sun and the Sun itself constitute only a negligible part of the gigantic collective of stars and nebulae, which is called the Galaxy. We see this cluster of stars on clear moonless nights as a strip 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 that make up it fill a volume that has the shape of a highly compressed ellipsoid of revolution. Often in popular literature the shape of the Galaxy is compared to a biconvex lens. In fact, everything is much more complicated, and the picture drawn is too rough. In fact, it turns out that different types of stars are concentrated 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 intermediate cases. Nevertheless, it turns out that the main part of the stars in the Galaxy is located in a giant disk, the diameter of which is about 100 thousand light years, and the thickness is about 1500 light years. In this disk, there are slightly more than 150 billion stars of various types. Our Sun is one of these stars, located on the periphery of the Galaxy near 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 nucleus of the Galaxy (or its center) is about 30 thousand light years. The 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 greater than the average stellar density in the vicinity of the Sun ***. In addition, stars tend to form separate groups or clusters. A good example of such a cluster is the Pleiades, which are visible in our winter sky (Figure 3).

The Galaxy also contains structural details on a much larger scale. Recent studies have shown that nebulae, as well as hot massive stars, are distributed along the branches of the spiral. The spiral structure is especially well seen in other star systems - galaxies (with a small letter, in contrast to our star system - the Galaxy). One of these galaxies is shown in Fig. 4. Establishing the spiral structure of the Galaxy in which we ourselves find ourselves has proved extremely difficult.

The stars and nebulae within the Galaxy move in a rather complex way. 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 regions of the Galaxy have different periods of rotation. Thus, the Sun and the stars surrounding it in a huge area of several hundred light-years in size make a complete revolution in about 200 million years. Since the Sun, together with the family of planets, has apparently existed for about 5 billion years, during its evolution (from its birth from a gaseous nebula to its current state) it has made about 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, the age is blooming ...

The speed of the movement of the Sun and its neighboring stars along their almost circular galactic orbits reaches 250 km/s****. This regular movement around the galactic core is superimposed by the chaotic, erratic movements of the stars. The velocities of such movements are much less - about 10-50 km / s, and they are different for objects of different types. Hot massive stars have the least speed (6-8 km/s), solar-type stars have about 20 km/s. The lower these velocities, the flatter the distribution of this type of stars.

On the scale that we used to visualize the solar system, the dimensions of the Galaxy would be 60 million km - a value already quite close to the distance from the Earth to the Sun. From this it is clear that as one penetrates into more and more remote regions of the Universe, this scale is no longer suitable, since it loses visibility. 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. Recall that the radius of this orbit is 0.53 × 10 microscopic dimensions: 0.0046 A (angstrom is a unit of length equal to 10-8 cm).

We have already emphasized that the stars are separated from each other by great distances, and thus practically isolated. In particular, this means that the stars almost never collide with each other, although the movement of each of them is determined by the gravitational force field created by all the stars in the Galaxy. If we consider the Galaxy as a certain region filled with gas, with stars playing the role of gaseous molecules and atoms, then we must consider this gas to be extremely rarefied. In the vicinity of the Sun, the average distance between stars is about 10 million times greater than the average diameter of the stars. Meanwhile, under normal conditions in ordinary air, the average distance between molecules is only a few tens of times greater than the dimensions 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 the stellar density is relatively high, collisions between stars will occur from time to time. Here, approximately one collision should be expected every million years, while in the normal regions of the Galaxy during the entire history of the evolution of our stellar system, which is at least 10 billion years, there were practically no collisions between stars (see Chapter 9).

We have briefly outlined the scale and the most general structure of the stellar system to which our Sun belongs. At the same time, those methods were not considered at all, with the help of which for many years several generations of astronomers, step by step, recreated the majestic picture of the structure of the Galaxy. 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. Such a picture is essential to the understanding of this book.

For several decades, astronomers have been persistently studying other star systems that are more or less similar to ours. This area of research is called extragalactic astronomy. It now plays almost a leading role in astronomy. Over the past three decades, extragalactic astronomy has made astonishing progress. Little by little, the grandiose contours of the Metagalaxy began to emerge, in which our star system is included as a small particle. We still do not 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 deep theoretical research. Yet the overall structure of the Metagalaxy has largely become clear in recent years.

We can define the Metagalaxy as a collection of star systems - galaxies moving in the vast expanses of the part of the Universe that 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 with the total length 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 spot of light of the 5th magnitude *****.

In fact, this is a huge stellar world, in terms of the number of stars and the total mass of three times the size of our Galaxy, which in turn is a giant among galaxies. The distance to the Andromeda Nebula, or, as astronomers call it, M 31 (which means that in the well-known catalog of Messier nebulae it is listed under No. 31), is about 1800 thousand light years, which is about 20 times the size of the Galaxy. The M 31 nebula has a pronounced spiral structure and, in many of its characteristics, is very similar to our Galaxy. Near it are its small ellipsoidal satellites (Fig. 5). On fig. Figure 6 shows photographs of several galaxies relatively close to us. The great variety of their forms attracts attention. Along with spiral systems (such galaxies are denoted by the symbols Sa, Sb and Sc, depending on the nature of the development of the spiral structure; in the presence of a bridge passing through the nucleus (Fig. 6a), the letter B is placed after the letter S) there are spheroidal and ellipsoidal, devoid of any traces of the spiral structure , as well as irregular galaxies, a good example of which is the Magellanic Clouds.

Large telescopes observe a huge number of galaxies. If there are about 250 galaxies brighter than the visible 12th magnitude, then there are already about 50 thousand brighter than the 16th magnitude. The faintest objects that a reflecting telescope with a mirror diameter of 5 m can photograph at the limit are 24.5 magnitude. It turns out that among the billions of such weakest objects, the majority are galaxies. Many of them are distant from us at distances that light travels in 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 amazing objects come across among galaxies, for example, radio galaxies. These are star systems that radiate a huge amount of energy in the radio range. In some radio galaxies, the radio flux is several times greater than the optical flux, although in the optical range their luminosity is very high - several times greater than the total luminosity of our Galaxy. 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 light spots 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 removed from us at a great distance - 600 million light years. However, the flux of radio emission from Cygnus A at meter wavelengths is so great that it exceeds even the flux of radio emission from the Sun (during periods when there are no spots 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 you know, are inversely proportional to the squares of distances!

The spectra of most galaxies resemble the sun; in both cases, separate dark absorption lines are observed against a rather bright background. This is not surprising, since the radiation of galaxies is the radiation of billions of stars that are part of them, more or less similar to the Sun. Careful study of the spectra of galaxies many years ago led to one discovery of fundamental importance. The fact is that by the nature of the shift of the wavelength of any spectral line with respect to the laboratory standard, one can determine the speed of the radiating source along the line of sight. In other words, it is possible to establish with what speed the source is approaching or receding.

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 in galaxies (with the exception of a few closest to us) the spectral lines are always shifted to the long-wavelength part of the spectrum (redshift of the lines), and the magnitude of this shift is the greater, the further the galaxy is from us.

This means that all galaxies are moving away from us, and the expansion rate increases as the galaxies move away. It reaches enormous values. For example, the receding velocity of the Cygnus A radio galaxy found from the redshift is close to 17,000 km/s. Twenty-five years ago, the record belonged to the very faint (in optical rays of magnitude 20) radio galaxy ZC 295. In 1960, its spectrum was obtained. It turned out that the 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! The radio galaxy 3C 295 is at a distance from us that light travels in 5 billion years. Thus, astronomers studied the light that was emitted when the Sun and planets formed, and maybe even a little earlier ... Since then, even more distant objects have been discovered (ch. 6).

The reasons for the expansion of a system consisting of a huge number of galaxies, we will not touch 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 the analysis of the development of life in it (Chapter 7).

Superimposed on the general expansion of the system of galaxies are the erratic speeds of individual galaxies, usually equal to several hundred kilometers per second. That is why the galaxies closest to us do not exhibit a systematic redshift. After all, the velocities of random (so-called peculiar) motions for these galaxies are greater than the regular redshift velocity. The latter increases as the galaxies move away by about 50 km/s, for every million parsecs. Therefore, for galaxies whose distances do not exceed a few 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 the 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 included in a large cluster of galaxies, the center of which is located in that part of the sky on which the constellation Virgo is projected. This cluster has several thousand members and is one of the largest. On fig. Figure 8 shows a photograph of the famous cluster of galaxies in the constellation of the Northern Crown, numbering hundreds of galaxies. In the space between clusters, the density of galaxies is ten times less than inside clusters.

We think we study the stars
but it turned out that we are studying the atom.
R. Feynman

What is meant by the universe? What is the microcosm, macrocosm and megaworld and what are their scales? How are our possibilities limited when studying the large scales of the mega world and the smallest scales of the micro world?

Lesson-lecture

The image of the universe. The universe is understood as the totality of all objects that are somehow observed by man. Of these, only a few are accessible to observation with the help of the senses. This part of the world is called the macrocosm. The smallest objects (atoms, elementary particles) make up microworld. Objects that are gigantic and far away from us are called mega world.

Salvador Dali. nuclear cross

Make an assumption why S. Dali called his painting "Nuclear Cross".

world scales. The boundaries between these worlds are rather arbitrary. In order to visualize the objects of the macrocosm, microcosm and megaworld, we will mentally increase or decrease a certain sphere by a large number of times.

Let's start with a sphere with a radius of 10 cm. This is a typical size of a macroscopic object. In order to get to the boundaries of the known world quickly enough, we will have to increase and decrease the sphere many times over. Let's take a billion as such a large number.

1. Enlarging a sphere with a radius of 10 cm by a billion times, we get a sphere with a radius of 100,000 km. What are these dimensions? This is about a quarter of the distance from the Earth to the Moon. Such distances are quite accessible for human movement; Yes, astronauts have already landed on the moon. Everything that has dimensions of this order should be attributed to the macrocosm (Fig. 8).

Rice. 8 Scales of the macrocosm

2. Having made an increase by another billion times, we will get a sphere with a radius of 10 14 km. This. of course, astronomical dimensions. In astronomy, for the convenience of measuring distances, light units are used, which correspond to the time required for light to travel a certain distance.

What is a sphere with a radius of 10 St. years? The distance to the nearest star to us is approximately 4 sv. of the year. (The sun, of course, is also one of the stars, but in this case we do not consider it.) A sphere with a radius of 10 sv. years, the center of which is on the Sun, contains about a dozen stars. A distance of several light years is no longer available for human movement. At speeds achievable for humans (about 30 km / s), it takes about 40,000 years to get to the nearest star. Any other powerful engines, for example, those based on nuclear reactions, do not currently exist even in the project. So in the foreseeable future, humanity is forced to put up with the fact that moving to the stars is impossible.

Of course, a distance of 10 sv. years already belongs to the megaworld. Nevertheless, this is space closest to us. We know quite a lot about the stars closest to us: the distances to them, the temperature of their surface have been measured quite accurately, their composition, size and mass have been determined. Some stars have satellites - planets. This information was obtained by studying the emission spectra of these stars. We can say that a sphere with a radius of 10 sv. years of well-studied space.

3. Having made the next increase by a billion times, we will get a sphere with a radius of 10 billion sv. years. It is at this distance from us that the most distant objects that we can observe are located. Thus, we have obtained a sphere in which all the objects of the Universe that we observe lie. Note that objects at such a great distance from us are very bright luminaries; a star comparable to the Sun would not be visible even in the most powerful telescopes.

It is difficult to say what is outside this sphere. The generally accepted hypothesis says that we cannot observe objects that are more than 13 billion light years away from us at all. years. This fact is due to the fact that our Universe was born 13 billion years ago, so the light from more distant objects simply has not yet reached us. So, we have reached the borders of the mega world (Fig. 9).

Rice. 9. The scale of the mega world

The boundary of the Universe we observe is at a distance of approximately 10 billion light years. years.

We will now move into the depths of the microworld. Reducing the sphere with a radius of 10 cm by a billion times, we get a sphere with a radius of 10 -8 cm = 10 -10 m = 0.1 nm. It turns out that this is a characteristic scale for the microcosm. Atoms and the simplest molecules have sizes of this order. The microcosm of this scale is well studied. We know the laws that describe the interactions of atoms and molecules.

Objects of this size are inaccessible to observation with the naked eye and are not even visible in the most powerful microscopes, since the wavelength of visible light lies in the range of 300-700 nm, i.e., thousands of times greater than the size of objects. The structure of atoms and molecules is judged from indirect data, in particular, from the spectra of atoms and molecules. All pictures depicting atoms and molecules are the fruits of model images. Nevertheless, we can assume that the world of atoms and molecules - a world of about 0.1 nm in size - has already been studied quite well and no fundamentally new laws will appear in this world.

Of course, this world is not yet the limit of knowledge; for example, the dimensions of atomic nuclei are about 10,000 times smaller. By reducing the sphere with a radius of 0.1 nm by a billion times, we get a sphere with a radius of 10 -17 cm, or 10 -19 m. We have actually reached the limits of knowledge. The fact is that the sizes of the smallest particles of matter - electrons and quarks (we will talk about them in § 29) - are of the order of magnitude 10 -16 cm, i.e., slightly larger than our sphere. What is inside electrons and quarks, or, in other words, whether electrons and quarks are composite particles, is currently unknown. It is possible that the size of 10 -17 cm no longer corresponds to any real structural unit of the substance.

The laws that determine the motion and structure of matter on the scales of 10 -15 - 10 -16 cm have not yet been fully studied. Modern experimental possibilities do not allow even deeper penetration into the microworld.

What are the reasons for limiting our access to smaller scales? The fact is that the main method of studying the structure of microparticles is the observation of collisions between different particles. The laws of nature are such that at small distances particles repel each other. Therefore, the smaller scales scientists explore, the more energy must be imparted to the colliding particles. This energy is imparted during the acceleration of particles in accelerators, and the greater the energy to be imparted, the larger should be the dimensions of the accelerators. Modern accelerators are several kilometers in size. In order to advance even further into the depths of the microworld, accelerators the size of the globe are needed.

So, now you have to imagine what scale the microworld corresponds to (Fig. 10).

Microcosm 10. Scales of the microcosm

In the microcosm, in the macrocosm and in the megaworld, the laws of nature manifest themselves in different ways. Objects of the microcosm have both the properties of particles and the properties of waves; in the macrocosm and the megaworld such objects practically do not exist.

Why can't we look "beyond the horizon" of the Universe - to see objects that are more than 13 billion light years away from us? years?
What is common in the experimental methods of studying the mega-world and the micro-world?
Some microparticles live for 10 -18 s, after which they disintegrate. What is the corresponding light unit of length (the distance that light travels in this time) comparable to?

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