Around which the sun revolves. The speed of the sun and galaxy in the universe. Characteristics of the Milky Way Galaxy
Any person, even lying on the couch or sitting near the computer, is in constant motion. This continuous movement in outer space has a variety of directions and tremendous speeds. First of all, the Earth moves around its axis. In addition, the planet revolves around the sun. But that's not all. Much more impressive distances we overcome together with the solar system.
The sun is one of the stars in the plane of the Milky Way, or simply the Galaxy. It is 8 kpc away from the center, and the distance from the plane of the Galaxy is 25 pc. The stellar density in our region of the Galaxy is approximately 0.12 stars per 1 pc3. Position solar system is not constant: it is in constant motion relative to nearby stars, interstellar gas, and finally, around the center of the Milky Way. The movement of the solar system in the galaxy was first noticed by William Herschel.
Movement relative to nearby stars
The speed of movement of the Sun to the border of the constellations Hercules and Lyra is 4 a.s. per year, or 20 km/s. The velocity vector is directed towards the so-called apex - a point to which the movement of other nearby stars is also directed. Directions of velocities of stars, incl. The suns intersect at the point opposite to the apex, called the anti-apex.
Moving relative to visible stars
Separately, the movement of the Sun in relation to bright stars that can be seen without a telescope is measured. This is an indicator of the standard movement of the Sun. The speed of such movement is 3 AU. per year or 15 km/s.
Movement relative to interstellar space
In relation to interstellar space, the solar system is already moving faster, the speed is 22-25 km / s. At the same time, under the influence of the "interstellar wind", which "blowing" from the southern region of the Galaxy, the apex shifts to the constellation Ophiuchus. The shift is estimated at about 50.
Moving around the center of the Milky Way
The solar system is in motion relative to the center of our Galaxy. It moves towards the constellation Cygnus. The speed is about 40 AU. per year, or 200 km/s. It takes 220 million years for a complete revolution. It is impossible to determine the exact speed, because the apex (the center of the Galaxy) is hidden from us behind dense clouds of interstellar dust. The apex shifts 1.5° every million years, and completes a full circle in 250 million years, or 1 "galactic year.
Journey to the edge of the Milky Way
Movement of the Galaxy in outer space
Our Galaxy also does not stand still, but approaches the Andromeda galaxy at a speed of 100-150 km/s. A group of galaxies, which includes the Milky Way, is moving towards the large cluster of Virgo at a speed of 400 km/s. It is difficult to imagine, and even more difficult to calculate, how far we move every second. These distances are huge, and the errors in such calculations are still quite large.
You are sitting, standing or lying down reading this article, and you do not feel that the Earth is rotating around its axis at a breakneck speed - about 1,700 km / h at the equator. However, the rotation speed doesn't seem all that fast when converted to km/s. It turns out 0.5 km / s - a barely noticeable flash on the radar, in comparison with other speeds around us.
Just like other planets in the solar system, the Earth revolves around the Sun. And in order to stay in its orbit, it moves at a speed of 30 km / s. Venus and Mercury, which are closer to the Sun, move faster, Mars, whose orbit passes the orbit of the Earth, moves much more slowly.
But even the Sun does not stand in one place. Our Milky Way galaxy is huge, massive and also mobile! All stars, planets, gas clouds, dust particles, black holes, dark matter - all this moves relative to a common center of mass.
According to scientists, the Sun is located at a distance of 25,000 light years from the center of our galaxy and moves in an elliptical orbit, making a complete revolution every 220-250 million years. It turns out that the speed of the Sun is about 200-220 km / s, which is hundreds of times higher than the speed of the Earth around its axis and tens of times higher than the speed of its movement around the Sun. This is what the movement of our solar system looks like.
Is the galaxy stationary? Again no. Giant space objects have a large mass, and therefore create strong gravitational fields. Give the Universe a little time (and we had it - about 13.8 billion years), and everything will start moving in the direction of the greatest attraction. That is why the Universe is not homogeneous, but consists of galaxies and groups of galaxies.
What does this mean for us?
This means that the Milky Way is pulled towards itself by other galaxies and groups of galaxies located nearby. This means that massive objects dominate this process. And this means that not only our galaxy, but also all those around us are influenced by these "tractors". We are getting closer to understanding what happens to us in outer space, but we still lack facts, for example:
- what were the initial conditions under which the universe was born;
- how the various masses in the galaxy move and change over time;
- how the Milky Way and surrounding galaxies and clusters formed;
- and how it is happening now.
However, there is a trick that will help us figure it out.
The universe is filled with cosmic microwave background radiation with a temperature of 2.725 K, which has been preserved since the time of the Big Bang. In some places there are tiny deviations - about 100 μK, but the general temperature background is constant.
This is because the universe was formed in the Big Bang 13.8 billion years ago and is still expanding and cooling.
380,000 years after the Big Bang, the universe cooled to such a temperature that it became possible to form hydrogen atoms. Prior to this, photons constantly interacted with the rest of the plasma particles: they collided with them and exchanged energy. As the universe cools, there are fewer charged particles, and more space between them. Photons were able to move freely in space. Relic radiation is photons that were emitted by the plasma towards the future location of the Earth, but avoided scattering, since recombination has already begun. They reach the Earth through the space of the Universe, which continues to expand.
You can "see" this radiation yourself. The interference that occurs on an empty TV channel if you use a simple bunny-ear antenna is 1% due to CMB.
And yet the temperature of the background background is not the same in all directions. According to the results of the Planck mission research, the temperature differs somewhat in the opposite hemispheres of the celestial sphere: it is slightly higher in the areas of the sky south of the ecliptic - about 2.728 K, and lower in the other half - about 2.722 K.
Microwave background map made with the Planck telescope. This difference is almost 100 times greater than the rest of the observed CMB temperature fluctuations, and this is misleading. Why is this happening? The answer is obvious - this difference is not due to fluctuations in the background radiation, it appears because there is movement!
When you approach a light source or it approaches you, the spectral lines in the spectrum of the source shift towards short waves (violet shift), when you move away from it or it moves away from you, the spectral lines shift towards long waves (red shift).
The relic radiation cannot be more or less energetic, which means we are moving through space. The Doppler effect helps to determine that our solar system is moving relative to the CMB at a speed of 368 ± 2 km/s, and the local group of galaxies, including the Milky Way, the Andromeda Galaxy and the Triangulum Galaxy, is moving at a speed of 627 ± 22 km/s relative to the CMB. These are the so-called peculiar velocities of galaxies, which are several hundred km/s. In addition to them, there are also cosmological velocities due to the expansion of the Universe and calculated according to the Hubble law.
Thanks to the residual radiation from the Big Bang, we can observe that everything in the universe is constantly moving and changing. And our galaxy is only a part of this process.
We all know that the Earth revolves around the Sun. Based on this, a natural question arises: does the Sun itself rotate? And if so, around what? Astronomers received an answer to this question only in the 20th century.
Our star is really moving, and if the Earth has two circles of rotation (around the Sun and around its axis), then the Sun has three of them. Moreover, the entire solar system, together with the planets and other cosmic bodies, is gradually moving away from the center of the galaxy, moving several million kilometers with each revolution.
What does the sun move around?
What does the sun revolve around? It is known that our star is located, the diameter of which is about 30,000 parsecs. , equal to 3.26 light years.
In the central part of the Milky Way there is a relatively small Galactic center with a radius of about 1000 parsecs. Star formation is still taking place in it and the core is located, thanks to which our star system once arose.
The distance of the Sun from the Galactic center is 26 thousand light years, that is, it is located closer to the edges of the galaxy. Together with the rest of the stars that make up the Milky Way, the Sun revolves around this center. The average speed of its movement varies from 220 to 240 km per second.
One revolution around the central part of the galaxy takes an average of 200 million years. Over the entire period of its existence, our planet, together with the Sun, flew around the Galactic core only about 30 times.
Why does the sun revolve around the galaxy?
As with the Earth's rotation, the exact cause of the Sun's motion has not been established. According to one version, in the Galactic center there is some kind of dark matter (a supermassive black hole), which affects both the rotation of stars and their speed. Around this hole is another hole of smaller mass.
Together, both matter exert a gravitational influence on the stars in the galaxy and force them to move along different trajectories. Other scientists are of the opinion that the movement is due to gravitational forces emanating from the core of the Milky Way.
Like any object, the Sun moves by inertia along a straight path, but the gravity of the Galactic center attracts it to itself and thereby makes it rotate in a circle.
Does the sun rotate on its axis?
The rotation of the Sun around its axis is the second circle of its motion. Since it consists of gases, its movement is differentiated. 
In other words, the star rotates faster at its equator and slower at its poles. Tracking the rotation of the Sun around its axis is quite difficult, so scientists have to navigate by sunspots.
On average, a spot in the region of the solar equator rotates around the axis of the Sun and returns to its original position in 24.47 days. Regions in the region of the poles move around the solar axis in 38 days.
In order to calculate a specific value, scientists decided to focus on a position of 26 ° from the equator, since around this place there is the largest number sun spots. As a result, astronomers came to a single figure, according to which the speed of rotation of the Sun around its own axis is 25.38 days.
What is rotation around a balanced center?
As mentioned above, unlike the Earth, the Sun has three planes of rotation. The first is around the center of the galaxy, the second is around its axis, and the third is the so-called gravitational balanced center. If you explain in simple words, then all the planets revolving around the Sun, although they have a much smaller mass, but attract it a little towards themselves.
As a result of these processes, the Sun's own axis also rotates in space. During rotation, it describes the radius of the center balancing, within which it rotates. In this case, the Sun itself also describes its radius. The general picture of this movement is quite clear to astronomers, but its practical component has not been fully studied. 
In general, our star is a very complex and multifaceted system, so in the future, scientists will have to uncover many more of its secrets and mysteries.
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This article discusses the speed of the Sun and the Galaxy relative to different systems reference:
The speed of the Sun in the Galaxy relative to the nearest stars, visible stars and the center of the Milky Way;
Velocity of the Galaxy relative to the local group of galaxies, distant star clusters and cosmic background radiation.
Brief description of the Milky Way Galaxy.
Description of the Galaxy.
Before proceeding to the study of the speed of the Sun and the Galaxy in the Universe, let's get to know our Galaxy better.
We live, as it were, in a gigantic "star city". Or rather, our Sun “lives” in it. The population of this "city" is a variety of stars, and more than two hundred billion of them "live" in it. A myriad of suns are born in it, going through their youth, middle age and old age - they go through a long and difficult life path lasting billions of years.
The dimensions of this "star city" - the Galaxy are enormous. The distances between neighboring stars are, on average, thousands of billions of kilometers (6*1013 km). And there are more than 200 billion such neighbors.
If we raced from one end of the Galaxy to the other at the speed of light (300,000 km/sec), it would take about 100,000 years.
Our entire star system slowly rotates like a giant wheel made up of billions of suns.
Orbit of the Sun
At the center of the Galaxy, apparently, there is a supermassive black hole(Sagittarius A *) (about 4.3 million solar masses) around which, presumably, a black hole of average mass from 1,000 to 10,000 solar masses rotates with an orbital period of about 100 years and several thousand relatively small ones. Their combined gravitational action on neighboring stars causes the latter to move along unusual trajectories. There is an assumption that most galaxies have supermassive black holes in their core.
The central regions of the Galaxy are characterized by a strong concentration of stars: each cubic parsec near the center contains many thousands of them. Distances between stars are tens and hundreds of times less than in the vicinity of the Sun.
The core of the Galaxy with great force attracts all other stars. But a huge number of stars are settled throughout the "star city". And they also attract each other in different directions, and this has a complex effect on the movement of each star. Therefore, the Sun and billions of other stars mostly move in circular paths or ellipses around the center of the Galaxy. But that's just "basically" - if we look closely, we'd see them moving in more complex curved, meandering paths among the surrounding stars.
Feature of the Milky Way Galaxy:
Location of the Sun in the Galaxy.
Where in the Galaxy is the Sun and does it move (and with it the Earth, and you and me)? Are we in the "city center" or at least somewhere close to it? Studies have shown that the Sun and the solar system are located at a great distance from the center of the Galaxy, closer to the "urban outskirts" (26,000 ± 1,400 light years).
The Sun is located in the plane of our Galaxy and is removed from its center by 8 kpc and from the plane of the Galaxy by about 25 pc (1 pc (parsec) = 3.2616 light years). In the region of the Galaxy where the Sun is located, the stellar density is 0.12 stars per pc3.
model of our galaxy
The speed of the Sun in the Galaxy.
The speed of the Sun in the Galaxy is usually considered relative to different frames of reference:
relative to nearby stars.
Relative to all bright stars visible to the naked eye.
Regarding interstellar gas.
Relative to the center of the Galaxy.
1. The speed of the Sun in the Galaxy relative to the nearest stars.
Just as the speed of a flying aircraft is considered in relation to the Earth, not taking into account the flight of the Earth itself, so the speed of the Sun can be determined relative to the stars closest to it. Such as the stars of the Sirius system, Alpha Centauri, etc.
This velocity of the Sun in the Galaxy is relatively small: only 20 km/sec or 4 AU. (1 astronomical unit is equal to the average distance from the Earth to the Sun - 149.6 million km.)
The Sun, relative to the nearest stars, moves towards a point (apex) lying on the border of the constellations Hercules and Lyra, approximately at an angle of 25 ° to the plane of the Galaxy. Equatorial coordinates of the apex = 270°, = 30°.
2. The speed of the Sun in the Galaxy relative to the visible stars.
If we consider the movement of the Sun in the Milky Way Galaxy relative to all the stars visible without a telescope, then its speed is even less.
The speed of the Sun in the Galaxy relative to the visible stars is 15 km/sec or 3 AU.
The apex of the motion of the Sun in this case also lies in the constellation Hercules and has the following equatorial coordinates: = 265°, = 21°.
The speed of the Sun relative to nearby stars and interstellar gas
3. The speed of the Sun in the Galaxy relative to the interstellar gas.
The next object of the Galaxy, with respect to which we will consider the speed of the Sun, is interstellar gas.
The expanses of the universe are far from being as desolate as it was thought for a long time. Although in small quantities, but everywhere there is interstellar gas, filling all corners of the universe. The interstellar gas, with the apparent emptiness of the unfilled space of the Universe, accounts for almost 99% of the total mass of all space objects. Dense and cold forms of interstellar gas containing hydrogen, helium and minimal volumes heavy elements(iron, aluminum, nickel, titanium, calcium) are in a molecular state, connecting into vast cloud fields. Usually, in the composition of the interstellar gas, the elements are distributed as follows: hydrogen - 89%, helium - 9%, carbon, oxygen, nitrogen - about 0.2-0.3%.
A tadpole-like cloud of interstellar gas and dust IRAS 20324+4057 that hides a growing star
Clouds of interstellar gas can not only rotate in an orderly manner around galactic centers, but also have unstable acceleration. Over the course of several tens of millions of years, they catch up with each other and collide, forming complexes of dust and gas.
In our Galaxy, the main volume of interstellar gas is concentrated in spiral arms, one of the corridors of which is located near the solar system.
The speed of the Sun in the Galaxy relative to the interstellar gas: 22-25 km/sec.
Interstellar gas in the immediate vicinity of the Sun has a significant intrinsic velocity (20-25 km/s) relative to the nearest stars. Under its influence, the apex of the Sun's motion shifts towards the constellation Ophiuchus (= 258°, = -17°). The difference in direction of movement is about 45°.
4. The speed of the Sun in the Galaxy relative to the center of the Galaxy.
In the three points discussed above, we are talking about the so-called peculiar, relative speed of the Sun. In other words, peculiar speed is the speed relative to the cosmic frame of reference.
But the Sun, the stars closest to it, and the local interstellar cloud are all involved in a larger movement - movement around the center of the Galaxy.
And here is the speech goes already about very different speeds.
The speed of the Sun around the center of the Galaxy is huge by earthly standards - 200-220 km / s (about 850,000 km / h) or more than 40 AU. / year.
It is impossible to determine the exact speed of the Sun around the center of the Galaxy, because the center of the Galaxy is hidden from us behind dense clouds of interstellar dust. However, more and more new discoveries in this area are decreasing the estimated speed of our sun. More recently, they talked about 230-240 km / s.
The solar system in the galaxy is moving towards the constellation Cygnus.
The motion of the Sun in the Galaxy occurs perpendicular to the direction to the center of the Galaxy. Hence the galactic coordinates of the apex: l = 90°, b = 0° or in more familiar equatorial coordinates - = 318°, = 48°. Since this is a reversal motion, the apex shifts and completes a full circle in a "galactic year", approximately 250 million years; its angular velocity is ~5" / 1000 years, i.e. the coordinates of the apex shift by one and a half degrees per million years.
Our Earth is about 30 such "galactic years" old.
The speed of the Sun in the Galaxy relative to the center of the Galaxy
By the way, an interesting fact about the speed of the Sun in the Galaxy:
The speed of rotation of the Sun around the center of the Galaxy almost coincides with the speed of the compression wave that forms the spiral arm. Such a situation is atypical for the Galaxy as a whole: the spiral arms rotate at a constant angular velocity, like spokes in wheels, and the movement of stars occurs with a different pattern, so almost the entire stellar population of the disk either gets inside the spiral arms or falls out of them. The only place where the speeds of stars and spiral arms coincide is the so-called corotation circle, and it is on it that the Sun is located.
For the Earth, this circumstance is extremely important, since violent processes occur in the spiral arms, which form powerful radiation that is destructive to all living things. And no atmosphere could protect him from it. But our planet exists in a relatively quiet place in the Galaxy and has not been affected by these cosmic cataclysms for hundreds of millions (or even billions) of years. Perhaps that is why life was able to originate and survive on Earth.
The speed of movement of the Galaxy in the Universe.
The speed of movement of the Galaxy in the Universe is usually considered relative to different frames of reference:
Relative to the Local Group of galaxies (speed of approach to the Andromeda galaxy).
Relative to distant galaxies and clusters of galaxies (the speed of movement of the Galaxy as part of the local group of galaxies to the constellation Virgo).
Regarding the relic radiation (the speed of movement of all galaxies in the part of the Universe closest to us to the Great Attractor - a cluster of huge supergalaxies).
Let's take a closer look at each of the points.
1. Velocity of movement of the Milky Way Galaxy towards Andromeda.
Our Milky Way Galaxy also does not stand still, but is gravitationally attracted and approaches the Andromeda galaxy at a speed of 100-150 km/s. The main component of the speed of approach of galaxies belongs to the Milky Way.
The lateral component of the motion is not precisely known, and it is premature to worry about a collision. An additional contribution to this motion is made by the massive galaxy M33, located approximately in the same direction as the Andromeda galaxy. In general, the speed of our Galaxy relative to the barycenter of the Local Group of galaxies is about 100 km / s approximately in the Andromeda/Lizard direction (l = 100, b = -4, = 333, = 52), however, these data are still very approximate. This is a very modest relative speed: the Galaxy is displaced by its own diameter in two or three hundred million years, or, very approximately, in a galactic year.
2. Velocity of movement of the Milky Way Galaxy towards the Virgo cluster.
In turn, the group of galaxies, which includes our Milky Way, as a whole, is moving towards the large cluster of Virgo at a speed of 400 km/s. This movement is also due to gravitational forces and is carried out relative to distant clusters of galaxies.
Velocity of the Milky Way Galaxy towards the Virgo Cluster
3. Speed of movement of the Galaxy in the Universe. To the Great Attractor!
Relic radiation.
According to the Big Bang theory, the early Universe was a hot plasma consisting of electrons, baryons, and constantly emitted, absorbed, and re-emitted photons.
As the Universe expanded, the plasma cooled down and at a certain stage, slowed down electrons got the opportunity to combine with slowed down protons (hydrogen nuclei) and alpha particles (helium nuclei), forming atoms (this process is called recombination).
This happened at a plasma temperature of about 3,000 K and an approximate age of the universe of 400,000 years. There is more free space between particles, there are fewer charged particles, photons no longer scatter so often and can now move freely in space, practically without interacting with matter.
Those photons that were emitted at that time by the plasma towards the future location of the Earth still reach our planet through the space of the universe that continues to expand. These photons make up the relic radiation, which is thermal radiation that evenly fills the Universe.
The existence of relic radiation was predicted theoretically by G. Gamow within the framework of the theory big bang. Its existence was experimentally confirmed in 1965.
Velocity of movement of the Galaxy relative to the cosmic background radiation.
Later, the study of the speed of movement of galaxies relative to the cosmic background radiation began. This movement is determined by measuring the non-uniformity of the temperature of the relict radiation in different directions.
The radiation temperature has a maximum in the direction of motion and a minimum in the opposite direction. The degree of deviation of the temperature distribution from isotropic (2.7 K) depends on the magnitude of the velocity. It follows from the analysis of the observational data that the Sun moves relative to the cosmic microwave background at a speed of 400 km/s in the direction =11.6, =-12.
Such measurements also showed another important thing: all galaxies in the part of the Universe closest to us, including not only ours local group, but also the Virgo cluster and other clusters, move relative to the background cosmic microwave background at an unexpectedly high speed.
For the Local Group of galaxies, it is 600-650 km / s with an apex in the constellation Hydra (=166, =-27). It looks like that somewhere in the depths of the Universe there is a huge cluster of many superclusters that attract the matter of our part of the Universe. This cluster was named Great Attractor- from English word"attract" - to attract.
Since the galaxies that make up the Great Attractor are hidden by interstellar dust that is part of the Milky Way, mapping of the Attractor was only possible in last years using radio telescopes.
The Great Attractor is located at the intersection of several superclusters of galaxies. The average density of matter in this region is not much greater than the average density of the Universe. But due to its gigantic size, its mass turns out to be so great and the force of attraction is so huge that not only our star system, but also other galaxies and their clusters nearby move in the direction of the Great Attractor, forming a huge stream of galaxies.
The speed of movement of the Galaxy in the Universe. To the Great Attractor!
So, let's sum up.
The speed of the Sun in the Galaxy and the Galaxy in the Universe. Pivot table.
Hierarchy of movements in which our planet takes part:
The rotation of the Earth around the Sun;
Rotation together with the Sun around the center of our Galaxy;
Movement relative to the center of the Local Group of galaxies together with the entire Galaxy under the influence of the gravitational attraction of the constellation Andromeda (galaxy M31);
Movement towards a cluster of galaxies in the constellation Virgo;
Movement to the Great Attractor.
The speed of the Sun in the Galaxy and the speed of the Milky Way Galaxy in the Universe. Pivot table.
It is difficult to imagine, and even more difficult to calculate, how far we move every second. These distances are huge, and the errors in such calculations are still quite large. Here is what science has to date.
Before Nicolaus Copernicus (1473-1543), scientists believed that the Earth is in the center of the World, and all the planets, then there were five of them (Mercury, Venus, Mars, Jupiter and Saturn) and the Sun revolve around the Earth. I'm not talking about the hypotheses of finding the Earth on the back of an elephant, a turtle, or any other reptiles or mammals.
In the year of Copernicus's death (1543), his multi-volume work "On the Revolution of the Celestial Spheres" was published in Latin with a description new system of the universe, in the center of which was the Sun, and all the planets, already six in number (with the addition of the five known planets and the Earth) rotate in circular orbits around the center - the Sun.
The next step in the construction of the solar system was made in 1609 by Johannes Kepler (1571-1630), who proved, using accurate astrometric observations of the motion of the planets (mainly made by the Danish astronomer Tycho Brahe (1546-1601), that the planets do not move in circles, but in ellipses with the sun at their focus.
Experimental, i.e. observational, confirmation of the Copernican theory was obtained by Galileo Galilei (1564–1642), who observed the phases of Venus and Mercury through a telescope, which confirmed the Copernican (i.e., heliocentric) system of the universe.
And finally, Isaac Newton (1642-1727) brought differential equations celestial mechanics, which made it possible to calculate the coordinates of the planets of the solar system and explained why they move, in a first approximation, along ellipses. Later, the works of the great mechanics and mathematicians of the 18th and 19th centuries created a theory of perturbations, which made it possible to take into account the gravitational interaction of planets with each other. In this way, by comparing observations and calculations, the distant planets Neptune (Adams and Le Verrier, 1856) and Pluto (1932) were discovered, although last year Pluto was administratively deleted from the list of planets. Today, there are already six non-Neptunean planets the size of Pluto and even a little more.
By the middle of the 19th century, the astrometric accuracy of determining the coordinates of stars had reached hundredths of an arc second. Then for some bright stars it was noticed that their coordinates differ from those measured several centuries earlier. The first such antique catalog was that of Hipparchus and Ptolemy (190 BC) and, in a much later era of the early Renaissance, that of Ulugbek (1394–1449). The concept of “proper motion of stars” appeared, which before that, and even now, are traditionally called “fixed stars”.
Carefully studying these proper motions, William Herschel (1738–1822) drew attention to their systematic distribution and drew a correct and highly non-trivial conclusion from this: part of the proper motion of stars is not the motion of these stars, but a reflection of the motion of our Sun relatively close to the Sun stars. Similarly, we see the movement of nearby trees relative to distant trees when we drive a car (or, even better, a horse) along a forest road.
By increasing the number of stars with measured proper motions, it was possible to determine that our Sun flies in the direction of the constellation Hercules, to a point called the apex, with coordinates α= 270° and δ= 30°, at a speed of 19.2 km/s. This is the own "peculiar" motion of the Sun with all the planets, interplanetary dust, asteroids relative to about a hundred stars closest to us. The distances to these stars are small, something on the order of 100-300 light years. All these stars are participating in general movement around the center of our Galaxy at a speed of about 250 km/s. The center of the Galaxy itself is located in the constellation Sagittarius, at a distance of about 25 thousand light years from the Sun. The movement of the Sun among the stars resembles the movement of a midge in a cloud, while the entire cloud flies with much greater speed relative to the trees in the forest.
Of course, our entire giant Galaxy itself flies relative to other galaxies. The speeds of individual galaxies reach hundreds and thousands of km/s. Some galaxies are approaching us, such as the famous Andromeda Nebula, while others are moving away from us.
All galaxies and clusters of galaxies also participate in the general cosmological expansion, which is noticeable, however, only at scales of more than 10–30 million light years. The magnitude of this expansion velocity depends linearly on the distance between galaxies or their clusters and is, according to modern measurements, about 25 km/s at a distance between galaxies of a million light years.
It is possible, however, to single out a special reference system, namely, the field of the relic 3K submillimeter radiation. Where we fly, the temperature of this radiation is slightly higher, and where we fly - lower. The difference between these temperatures is 0.006706 K. This is the so-called "dipole component" of the CMB anisotropy. The velocity of the Sun relative to the cosmic background radiation is 627 ± 22 km/s, and without taking into account the motion of the Local Group of galaxies - 370 km/s in the direction of the Virgo constellation.
So the question of where our Sun is flying and at what speed is difficult to answer. It is necessary to immediately determine: with respect to what and in what coordinate system.
In 1961, our group from the State Astronomical Institute. P. K. Sternberg of Moscow State University carried out observations of scattered solar ultraviolet radiation in the lines of hydrogen (1215A) and oxygen (1300A) from high-altitude geophysical rockets that rose to a height of 500 km. At that time, thanks to the proposal of Academician S.P. Korolev, the Soviet Union began to systematically launch interplanetary stations, both flyby and landing, to Mars and Venus. Naturally, we also decided to try to detect the same extended hydrogen coronas near Venus and Mars as on Earth.
With these launches, we were able to trace traces of neutral atomic hydrogen up to 125,000 km from the Earth, i.e., up to 25 Earth radii. The density of hydrogen at such distances from the Earth was only about 1 atom per cm 3, which is 19 orders of magnitude less than the concentration of air at sea level! However, to our great surprise, it turned out that the intensity of the scattered radiation in the Lyman-alpha line with a wavelength of 1215 A does not drop to zero at even greater distances, but remains constant and rather high, and the intensity changes by a factor of 2, depending on whether where our little telescope was looking.
At first, we assumed that it was the shining of distant stars, but the calculation showed that such a glow should be many orders of magnitude lower. A negligible amount of cosmic dust in the interstellar medium would completely “eat up” this radiation. The extended solar corona, according to the theory, should have been almost completely ionized, and there should not have been any neutral atoms there.
All that remained was the interstellar medium, which near the Sun could be largely neutral, which explained the effect we discovered. Two years after our publication, J.-E. Blamont and J.-J. Berto from the Aeronomy Service of France from the American satellite OGO-V discovered the geometric parallax of the region of maximum glow in the Lyman-alpha line, which made it possible to immediately estimate the distances to it. This value turned out to be approximately 25 astronomical units. The coordinates of this maximum were also determined. The picture began to clear up. A decisive contribution to this problem was made by two German physicists, P. V. Bloom and H. J. Fahr, who pointed out the role of the motion of the Sun relative to the interstellar medium. In order to measure all the parameters of this movement, in 1975 we, together with the already mentioned French specialists, carried out two special experiments on the domestic satellites Prognoz-5 and Prognoz-6. These satellites made it possible to obtain a map of the entire sky in the Lyman-alpha line, as well as to measure the temperature of neutral hydrogen atoms in the interstellar medium. The density of these atoms was determined "at infinity", i.e., far from the Sun, the speed and direction of the Sun's motion relative to the local interstellar medium.
The density of atoms turned out to be 0.06 atoms/cm3, and the speed was 25 km/s. A theory was also developed for the penetration of atoms of the interstellar medium into the solar system. It turned out that neutral hydrogen atoms, flying near the Sun along hyperbolic trajectories, are ionized by two mechanisms. The first of them is photoionization by ultraviolet and X-ray radiation of the Sun with wavelengths shorter than 912 A, and the second mechanism is recharging (electron exchange) with solar wind protons that permeate the entire solar system. The second ionization mechanism turned out to be 2–3 times more efficient than the first one. Solar wind stops interstellar magnetic field approximately at a distance of 100 astronomical units, and the interstellar medium running into the solar system at a distance of 200 AU.
Between these two shock waves (probably supersonic) there is a region of very hot, fully ionized plasma with a temperature of 10 7 or even 10 8 K. The question of the interaction of incident neutral hydrogen atoms with hot plasma in this intermediate region is extremely interesting. When interstellar, relatively cold atoms of the interstellar medium are recharged with hot protons, neutral atoms are formed in this region with very high temperature and corresponding speed given above. They permeate the entire solar system and can be registered near the Earth. For this purpose, a special Earth satellite, IBEX, was launched in the United States two years ago, successfully working to solve these and related problems. The effect of the "running" of the interstellar medium discovered by us was called the "interstellar wind".
In order to get around this unclear question, our group carried out a cycle of observations with the Prognoz satellite in the neutral helium line with a wavelength of 584A. Helium does not participate in the process of charge exchange with solar wind protons and is almost not ionized by solar ultraviolet. It is due to this that the atoms of neutral helium, flying along the hyperbolas past the Sun, are focused behind it, forming a cone with an increased density, which we observed. The axis of this cone gives us the direction of motion of the Sun relative to the local interstellar medium, and its divergence makes it possible to determine the temperature of helium atoms in the interstellar medium far from the Sun.
Our results for helium agreed perfectly with those for atomic hydrogen. The density of atomic helium "at infinity" turned out to be equal to 0.018 atom/cm 3 , which made it possible to determine the degree of ionization of atomic hydrogen, assuming that the abundance of helium is equal to the standard for the interstellar medium. This corresponds to 10–30% of the degree of atomic hydrogen ionization. The density and temperature of atomic hydrogen found by us exactly correspond to the zone of neutral hydrogen with a slightly increased temperature - 12000 K.
In 2000, German astronomers led by H. Rosenbauer were able to directly detect neutral helium atoms flying into the solar system from the interstellar medium on the Ulysses extra-ecliptic spacecraft. They determined the parameters of the "interstellar wind" (the density of atomic helium, the speed and direction of the Sun relative to the local interstellar medium). The results of direct measurements of helium atoms are in excellent agreement with our optical measurements.
Such is the story of the discovery of another movement of our Sun.
