All people experience mixed feelings when they look into the starry sky on a clear night. All the problems of an ordinary person begin to seem insignificant, and everyone begins to think about the meaning of their existence. The night sky seems overwhelmingly huge, but in reality we can only see the immediate surroundings.
This is Earth. This is where we live. 
And this is where we are in our solar system. 
Scaled distance between the Earth and the Moon. Doesn't look too big, right? 
It's worth thinking again though. Within this distance you can place
all the planets of our solar system, beautiful and neat.
But the size of the Earth (well, six Earths) compared to Saturn. 
If our planet had rings like Saturn, they would look like this. 
There are tons of comets between our planets.
This is what one of them looks like compared to Los Angeles.
But this is still nothing compared to our Sun. Just take a look. 
This is what we look like from Mars. 
Looking out from behind the rings of Saturn. 
This is what our planet looks like from the edge of the solar system. 
Comparison of the scales of the Earth and the Sun. It's scary, isn't it? 
And here is the same Sun from the surface of Mars. 
But that's nothing. They say there are more stars in space than there are grains of sand on all the beaches on Earth. 
And there are stars much larger than our little Sun. Just look how tiny it is compared to the star in the constellation Canis Major. 
But none of them can compare with the size of the galaxy.
If you reduce the Sun to the size of a white blood cell and reduce
in the same ratio, the Milky Way Galaxy would be the size of the United States.
The Milky Way is huge. We are somewhere here. 
But that's all we can see. 
However, even our galaxy is short compared to some others. Here's the Milky Way compared to IC 1011. 
Just think about everything that could be inside there.
Go ahead. There are thousands upon thousands of galaxies in this Hubble image, each containing millions of stars, each with its own planets.
Just keep in mind - an illustration of a very small part of the universe.
A small part of the night sky. 
And it is quite possible to assume that there are black holes there.
Here's the size of the black hole compared to Earth's orbit, just for fun
So if you're ever upset that you missed out
your favorite TV show... just remember...
This is your home
This is your home on the scale of the solar system 
And this is what happens if you zoom out. 
Let's continue... 
And a bit more... 
Almost... 
And here it is. That's all there is in the observable Universe.
And this is our place in it. Just a tiny ant in a giant jar 
Throughout the history of science, the interests of geoscience have included developing ideas about the world around humans - planet Earth, the solar system, the Universe. The first mathematically substantiated model of the universe was the geocentric system of C. Ptolemy (165-87 BC), which correctly for that time reflected the part of the world accessible to direct observation. Only 1500 years later, the heliocentric model of the solar system of N. Copernicus (1473-1543) was established.
Advances in physical theory and astronomy at the end of the 19th century. and the advent of the first optical telescopes led to the creation of ideas about an unchanging Universe. The development of the theory of relativity and its application to the solution of cosmological paradoxes (gravitational, photometric) created a relativistic theory of the Universe, which was initially presented by A. Einstein as a static model. In 1922-1924 gt. A.A. Friedman obtained solutions to the equations of the general theory of relativity for matter uniformly filling all space (model of a homogeneous isotropic Universe), which showed the non-stationary nature of the Universe - it must expand or contract. In 1929, E. Hubble discovered the expansion of the Universe, refuting the idea of its inviolability. The theoretical results of A.A. Friedman and E. Hubble made it possible to introduce the concept of “beginning” into the evolution of the Universe and explain its structure.
In 1946-1948. G. Gamow developed the theory of the “hot” Universe, according to which at the beginning of evolution the matter of the Universe had a temperature and density that were unattainable experimentally. In 1965, relict microwave background radiation was discovered, which initially had a very high temperature, which experimentally confirmed G. Gamow’s theory.
This is how our ideas about the world expanded in spatial and temporal terms. If for a long time the Universe was considered as an environment that included celestial bodies of various ranks, then according to modern ideas, the Universe is an ordered system developing unidirectionally. Along with this, the assumption arose that the Universe does not necessarily exhaust the concept of the material world and perhaps there are other Universes where the known laws of the universe do not necessarily apply.
Universe
Universe- this is the material world around us, limitless in time and space. The boundaries of the Universe will most likely expand as new opportunities for direct observation emerge, i.e. they are relative for each moment in time.
The Universe is one of the concrete scientific objects of experimental research. The fundamental laws of natural science are assumed to be true throughout the universe.
State of the Universe. The Universe is a non-stationary object, the state of which depends on time. According to the prevailing theory, the Universe is currently expanding: most galaxies (with the exception of those closest to ours) are moving away from us and relative to each other. The farther away the galaxy - the source of radiation - is located, the greater the speed of retreat (scattering). This dependence is described by the Hubble equation:
Where v- removal speed, km/s; R- distance to the galaxy, St. year; N - proportionality coefficient, or Hubble constant, H = 15×10 -6 km/(s×sa. year). It has been established that the acceleration speed increases.
One of the proofs of the expansion of the Universe is the “red shift of spectral lines” (Doppler effect): spectral absorption lines in objects moving away from the observer are always shifted towards long (red) waves of the spectrum, and approaching ones - towards short (blue).
Spectral absorption lines from all galaxies are inherently redshifted, which means expansion occurs.
Density of matter in the Universe. The distribution of matter density in individual parts of the Universe differs by more than 30 orders of magnitude. The highest density, if you do not take into account the microcosm (for example, the atomic nucleus), is inherent in neutron stars (about 10 14 g/cm 3), the lowest (10 -24 g/cm 3) - in the Galaxy as a whole. According to F.Yu. Siegel, the normal density of interstellar matter in terms of hydrogen atoms is one molecule (2 atoms) per 10 cm 3, in dense clouds - nebulae it reaches several thousand molecules. If the concentration exceeds 20 hydrogen atoms per 1 cm 3, then the process of convergence begins, developing into accretion (sticking together).
Material composition. Of the total mass of matter in the Universe, only about 1/10 is visible (luminous), the remaining 9/10 is invisible (non-luminous) matter. Visible matter, the composition of which can be confidently judged by the nature of the emission spectrum, is represented mainly by hydrogen (80-70%) and helium (20-30%). There are so few other chemical elements in the luminous mass of matter that they can be neglected. There is no significant amount of antimatter found in the Universe, with the exception of a small fraction of antiprotons in cosmic rays.
The universe is filled with electromagnetic radiation, which is called relict, those. left over from the early stages of the evolution of the Universe.
Homogeneity, isotropy and structure. On a global scale, the Universe is considered isotropic And homogeneous. A sign of isotropy, i.e. The independence of the properties of objects from the direction in space is the uniformity of the distribution of relict radiation. The most accurate modern measurements have not detected deviations in the intensity of this radiation in different directions and depending on the time of day, which at the same time indicates the great homogeneity of the Universe.
Another feature of the Universe is heterogeneity And structure(discreteness) on a small scale. On a global scale of hundreds of megaparsecs, the matter of the Universe can be considered as a homogeneous continuous medium, the particles of which are galaxies and even clusters of galaxies. A more detailed examination reveals the structured nature of the Universe. The structural elements of the Universe are cosmic bodies, primarily stars, forming stellar systems of different ranks: galaxy- galaxy cluster- Metagalaxy, They are characterized by localization in space, movement around a common center, a certain morphology and hierarchy.
The Milky Way Galaxy consists of 10 11 stars and the interstellar medium. It belongs to spiral systems that have a plane of symmetry (the plane of the disk) and an axis of symmetry (the axis of rotation). The oblateness of the Galaxy's disk, observed visually, indicates a significant speed of its rotation around its axis. The absolute linear speed of its objects is constant and equal to 220-250 km/s (it is possible that it increases for objects very distant from the center). The period of rotation of the Sun around the center of the Galaxy is 160-200 million years (on average 180 million years) and is called galactic year.
Evolution of the Universe. In accordance with the model of the expanding Universe, developed by A.A. Friedman on the basis of A. Einstein’s general theory of relativity, it has been established that:
1) at the beginning of evolution, the Universe experienced a state of cosmological singularity, when the density of its matter was equal to infinity and the temperature exceeded 10 28 K (with a density of over 10 93 g/cm 3 the matter has unexplored quantum properties of space-time and gravity);
2) a substance in a singular state underwent a sudden expansion, which can be compared to an explosion (“Big Bang”);
3) under conditions of nonstationarity of the expanding Universe, the density and temperature of matter decrease with time, i.e. in the process of evolution;
4) at a temperature of the order of 10 9 K, nucleosynthesis took place, as a result of which chemical differentiation of matter occurred and the chemical structure of the Universe arose;
5) based on this, the Universe could not exist forever and its age is determined from 13 to 18 billion years.
solar system
Solar system - this is the Sun and a set of celestial bodies: 9 planets and their satellites (as of 2002 their number was 100), many asteroids, comets and meteors that revolve around the Sun or enter (like comets) into the Solar System. Basic information about the objects of the Solar system is contained in Fig. 3.1 and table. 3.1.
Table 3.1. Some physical parameters of the planets of the solar system
| Solar System Object | Distance from the Sun | radius, km | number of earth radii | weight, 10 23 kg | mass relative to Earth | average density, g/cm 3 | orbital period, number of Earth days | period of rotation around its axis | number of satellites (moons) | albedo | acceleration of gravity at the equator, m/s 2 | speed of separation from the planet's gravity, m/s | presence and composition of the atmosphere, % | average surface temperature, °C | |
| million km | a.e. | ||||||||||||||
| Sun | - | 695 400 | 1.989×10 7 | 332,80 | 1,41 | 25-36 | 9 | - | 618,0 | Absent | |||||
| Mercury | 57,9 | 0,39 | 0,38 | 3,30 | 0,05 | 5,43 | 59 days | 0,11 | 3,70 | 4,4 | Absent | ||||
| Venus | 108,2 | 0,72 | 0,95 | 48,68 | 0,89 | 5,25 | 243 days | 0,65 | 8,87 | 10,4 | CO 2, N 2, H 2 O | ||||
| Earth | 149,6 | 1,0 | 1,0 | 59,74 | 1,0 | 5,52 | 365,26 | 23 h 56 min 4s | 0,37 | 9,78 | 11,2 | N 2, O 2, CO 2, Ar, H 2 O | |||
| Moon | 1,0 | 0,27 | 0,74 | 0,0123 | 3,34 | 29,5 | 27 h 32 min | - | 0,12 | 1,63 | 2,4 | Very dressed up | -20 | ||
| Mars | 227,9 | 1,5 | 0,53 | 6,42 | 0,11 | 3,95 | 24 h 37 min 23 s | 0,15 | 3,69 | 5,0 | CO 2 (95.3), N 2 (2.7), Ar (1.6), O 2 (0.15), H 2 O (0.03) | -53 | |||
| Jupiter | 778,3 | 5,2 | 18986,0 | 1,33 | 11.86 years | 9 h 30 min 30 s | 0,52 | 23,12 | 59,5 | N (77), Not (23) | -128 | ||||
| Saturn | 1429,4 | 9,5 | 5684,6 | 0,69 | 29.46 years | 10 hours 14 minutes | 0,47 | 8,96 | 35,5 | N, Not | -170 | ||||
| Uranus | 2871,0 | 19,2 | 25 362 | 868,3 | 1,29 | 84.07 years | 11 h3 | 0,51 | 8,69 | 21,3 | N (83), He (15), CH 4 (2) | -143 | |||
| Neptune | 4504,3 | 30,1 | 24 624 | 1024,3 | 1,64 | 164.8 years | 16h | 0,41 | 11,00 | 23,5 | N, He, CH 4 | -155 | |||
| Pluto | 5913,5 | 39,5 | 0,18 | 0,15 | 0,002 | 2,03 | 247,7 | 6.4 days | 0,30 | 0,66 | 1,3 | N2, CO, NH4 | -210 |
Sun is a hot gas ball, in which about 60 chemical elements were found (Table 3.2). The Sun rotates around its axis in a plane inclined at an angle of 7°15" to the plane of the Earth's orbit. The speed of rotation of the surface layers of the Sun is different: at the equator the period of revolution is 25.05 days, at a latitude of 30° - 26.41 days, in the polar regions - 36 days. The source of the Sun's energy is nuclear reactions that convert hydrogen into helium. The amount of hydrogen will ensure the preservation of its luminosity for tens of billions of years. Only one two-billionth of the solar energy reaches the Earth.
The sun has a shell structure (Fig. 3.2). In the center they highlight core with a radius of approximately 1/3 of the sun, a pressure of 250 billion atm, a temperature of more than 15 million K and a density of 1.5 × 10 5 kg/m 3 (150 times the density of water). Almost all of the sun's energy is generated in the core, which is transmitted through radiation zone, where light is repeatedly absorbed by a substance and re-emitted. Above is located convection zone(mixing), in which a substance begins to move due to uneven heat transfer (a process similar to the transfer of energy in a boiling kettle). The visible surface of the Sun is formed by its atmosphere. Its lower part with a thickness of about 300 km, emitting the bulk of the radiation, is called photosphere. This is the "coldest" place on the Sun with temperatures decreasing from 6000 to 4500 K in the upper layers. The photosphere is formed by granules with a diameter of 1000-2000 km, the distance between which is from 300 to 600 km. The granules create a general background for various solar formations - prominences, faculae, spots. Above the photosphere to an altitude of 14 thousand km is located chromosphere. During total lunar eclipses, it is visible as a pink halo surrounding a dark disk. The temperature in the chromosphere increases and in the upper layers reaches several tens of thousands of degrees. The outermost and thinnest part of the solar atmosphere is solar corona- extends over distances of several tens of solar radii. The temperature here exceeds 1 million degrees.
Table 3.2. Chemical composition of the Sun and terrestrial planets, % (according to A. A. Marakushev, 1999)
| Element | Sun | Mercury | Venus | Earth | Mars |
| Si | 34,70 | 16,45 | 33,03 | 31,26 | 36,44 |
| Fe | 30,90 | 63,07 | 30,93 | 34,50 | 24,78 |
| Mg | 27,40 | 15,65 | 31,21 | 29,43 | 34,33 |
| Na | 2,19 | - | - | - | - |
| Al | 1,74 | 0,97 | 2,03 | 1,90 | 2,29 |
| Ca | 1,56 | 0,88 | 1,62 | 1,53 | 1,73 |
| Ni | 0,90 | 2,98 | 1,18 | 1,38 | 0,43 |
Rice. 3.2. Structure of the Sun
Planets The solar system is divided into two groups: internal, or terrestrial planets - Mercury, Venus, Earth, Mars, and external, or giant planets - Jupiter, Saturn, Uranus, Neptune and Pluto. The estimated material composition of the planets is shown in Fig. 3.3.
Terrestrial planets. The inner planets have relatively small sizes, high density and internal differentiation of matter. They are distinguished by an increased concentration of carbon, nitrogen and oxygen, and a lack of hydrogen and helium. Terrestrial planets are characterized by tectonic asymmetry: the structure of the crust of the northern hemispheres of the planets differs from the southern ones.
Mercury - the planet closest to the Sun. Among the planets of the Solar System, it is distinguished by the most elongated elliptical orbit. The temperature on the illuminated side is 325-437°C, on the night side - from -123 to -185°C. The American spacecraft Mariner 10 in 1974 discovered a rarefied atmosphere on Mercury (pressure 10 -11 atm), consisting of helium and hydrogen in a ratio of 50:1. Mercury's magnetic field is 100 times weaker than Earth's, which is largely due to the planet's slow rotation around its axis. The surface of Mercury has much in common with the surface of the Moon, but the continental topography predominates. Along with lunar-like craters of various sizes, scarps that are absent on the Moon are noted - cliffs, 2-3 km high and hundreds and thousands of kilometers long.
Rice. 3.3. The structure and estimated material composition of the planets (according to G.V. Voitkevich): A - earth group: 1, 2, 3 - silicate, metal, metal sulfide substances, respectively; b- giants: 1 - molecular hydrogen; 2 - metallic hydrogen; 3 - water ice; 4 - core composed of stone or iron-stone material
The mass of Mercury is 1/18 of the mass of the Earth. Despite its small size, Mercury has an unusually high density (5.42 g/cm3), close to the density of the Earth. The high density indicates a hot, and likely molten, metallic core, which accounts for about 62% of the planet's mass. The core is surrounded by a silicate shell about 600 km thick. The chemical composition of the surface rocks and subsoil of Mercury can be judged only from indirect data. The reflectivity of the Mercury regolith indicates that it consists of the same rocks that make up the lunar soil.
Venus rotates around its axis even slower (in 244 Earth days) than Mercury, and in the opposite direction, so the Sun on Venus rises in the west and sets in the east. The mass of Venus is 81% of the earth's mass. The weight of objects on Venus is only 10% less than their weight on Earth. It is believed that the planet’s crust is thin (15-20 km) and its main part is represented by silicates, which are replaced at a depth of 3224 km by an iron core. The planet's topography is dissected - mountain ranges up to 8 km high alternate with craters with a diameter of tens of kilometers (maximum up to 160 km) and a depth of up to 0.5 km. Vast leveled spaces are covered with rocky scatterings of sharp-angled debris. A giant linear depression up to 1500 km long and 150 km wide with a depth of up to 2 km was discovered near the equator. Venus does not have a dipole magnetic field, which is explained by its high temperature. On the surface of the planet the temperature is (468+7)°C, and at depth, obviously, 700-800°C.
Venus has a very dense atmosphere. On the surface, the atmospheric pressure is at least 90-100 atm, which corresponds to the pressure of the earth’s seas at a depth of 1000 m. The chemical composition of the atmosphere consists mainly of carbon dioxide with an admixture of nitrogen, water vapor, oxygen, sulfuric acid, hydrogen chloride and hydrogen fluoride. It is believed that the atmosphere of Venus roughly corresponds to the earth’s in the early stages of its formation (3.8-3.3 billion years ago). The cloud layer of the atmosphere extends from a height of 35 km to 70 km. The lower layer of clouds consists of 75-80% sulfuric acid, in addition, hydrofluoric and hydrochloric acids are present. Being 50 million km closer than the Earth to the Sun, Venus receives twice as much heat as our planet - 3.6 cal/(cm 2 × min). This energy is accumulated by the carbon dioxide atmosphere, which causes a huge greenhouse effect and high temperatures of the Venusian surface - hot and, apparently, dry. Cosmic information indicates a peculiar glow of Venus, which is probably explained by the high temperatures of surface rocks.
Venus is characterized by complex cloud dynamics. There are probably powerful polar vortexes and strong winds at an altitude of about 40 km. Near the surface of the planet, the winds are weaker - about 3 m/s (obviously due to the absence of significant differences in surface temperature), which is confirmed by the absence of dust in the landing sites of the Venus station's descent modules. For a long time, the dense atmosphere did not allow us to judge the rocks of the Venusian surface. Analysis of the natural radioactivity of uranium, thorium and potassium isotopes in soils showed results close to those of terrestrial basalts and partially granites. Surface rocks are magnetized.
Mars is located 75 million km farther from the Sun than the Earth, so the Martian day is longer than the Earth's, and the amount of solar energy it receives is 2.3 times less compared to the Earth. The period of rotation around its axis is almost the same as that of the Earth. The inclination of the axis to the orbital plane ensures the change of seasons and the presence of “climatic” zones - a hot equatorial one, two temperate ones and two polar ones. Due to the small amount of incoming solar energy, the contrasts of thermal zones and seasons of the year are less pronounced than on Earth.
The density of the atmosphere of Mars is 130 times less than that of Earth and is only 0.01 atm. The atmosphere contains carbon dioxide, nitrogen, argon, oxygen, and water vapor. Daily temperature fluctuations exceed 100°C: at the equator during the day - about 10-20°C, and at the poles - below -100°C. Large temperature differences are observed between the day and night sides of the planet: from 10-30 to -120°C. At an altitude of about 40 km, Mars is surrounded by an ozone layer. A weak dipole magnetic field has been noted for Mars (at the equator it is 500 times weaker than the Earth's).
The surface of the planet is pitted with numerous craters of volcanic and meteorite origin. The average height difference is 12-14 km, but the huge caldera of the Nix Olympics volcano (Snows of Olympus) rises to 24 km. The diameter of its base is 500 km, and the diameter of the crater is 65 km. Some volcanoes are active. A peculiarity of the planet is the presence of huge tectonic cracks (for example, the Marineris Canyon, 4000 km long and 2000 km wide with a depth of up to 6 km), reminiscent of terrestrial grabens and morphosculptures corresponding to river valleys.
Images of Mars show areas that are light in color (“continental” areas, apparently composed of granites), yellow in color (“marine” areas, apparently composed of basalts) and snow-white in appearance (glacial polar caps). Observations of the polar regions of the planet have established variability in the outlines of ice massifs. According to scientists, the glacial polar caps are composed of frozen carbon dioxide and, possibly, water ice. The reddish color of the surface of Mars is probably due to hematitization and limonitization (iron oxidation) of rocks, which are possible in the presence of water and oxygen. Obviously, they come from the inside when the surface warms up during the day or with gas exhalations that melt the permafrost.
A study of rocks showed the following ratio of chemical elements (%): silica - 13-15, iron oxides - 12-16, calcium - 3-8, aluminum - 2-7, magnesium - 5, sulfur - 3, as well as potassium, titanium , phosphorus, chromium, nickel, vanadium. The composition of the soil on Mars is similar to some terrestrial volcanic rocks, but is enriched in iron compounds and depleted in silica. No organic formations were found on the surface. In the near-surface layers of the planet (from a depth of 50 cm), the soils are bound by permafrost, extending up to 1 km deep. In the depths of the planet, the temperature reaches 800-1500°C. It is assumed that at shallow depths the temperature should be 15-25 ° C, and the water may be in a liquid state. Under these conditions, the simplest living organisms can exist, traces of whose vital activity have not yet been found.
Mars has two satellites - Phobos (27x21x19 km) and Deimos (15x12x11 km), which are obviously fragments of asteroids. The orbit of the first is 5,000 km from the planet, the second is 20,000 km.
In table Figure 3.2 shows the chemical composition of the terrestrial planets. The table shows that Mercury is characterized by the highest concentrations of iron and nickel and the lowest silicon and magnesium.
Giant planets. Jupiter, Saturn, Uranus and Neptune are noticeably different from the terrestrial planets. In the giant planets, especially those closest to the Sun, the total angular momentum of the Solar system (in Earth units) is concentrated: Neptune - 95, Uranus - 64, Saturn - 294, Jupiter - 725. The distance of these planets from the Sun allowed them to retain a significant amount primary hydrogen and helium lost by the terrestrial planets under the influence of the “solar wind” and due to the insufficiency of their own gravitational forces. Although the density of the substance of the outer planets is small (0.7-1.8 g/cm 3), their volumes and masses are enormous.
The largest planet is Jupiter, which is 1300 times larger in volume and more than 318 times larger in mass than Earth. It is followed by Saturn, whose mass is 95 times the mass of the Earth. These planets contain 92.5% of the mass of all planets in the Solar System (71.2% for Jupiter and 21.3% for Saturn). The group of outer planets is completed by two twin giants - Uranus and Neptune. An important feature is the presence of rocky satellites on these planets, which probably indicates their external cosmic origin and is not associated with the differentiation of the substance of the planets themselves, formed by condensations primarily in the gaseous state. Many researchers believe that the central parts of these planets are rocky.
Jupiter with characteristic spots and stripes on the surface that are parallel to the equator and have variable outlines, it is the most accessible planet for exploration. The mass of Jupiter is only two orders of magnitude less than the Sun. The axis is almost perpendicular to the orbital plane.
Jupiter has a powerful atmosphere and a strong magnetic field (10 times stronger than the Earth’s), which determines the presence around the planet of powerful radiation belts of protons and electrons captured by Jupiter’s magnetic field from the “solar wind”. The atmosphere of Jupiter, in addition to molecular hydrogen and helium, contains various impurities (methane, ammonia, carbon monoxide, water vapor, phosphine molecules, hydrogen cyanide, etc.). The presence of these substances may be a consequence of the assimilation of heterogeneous material from Space. The layered hydrogen-helium mass reaches a thickness of 4000 km and, due to the uneven distribution of impurities, forms stripes and spots.
The huge mass of Jupiter suggests the presence of a powerful liquid or semi-liquid core of the asthenospheric type, which can be a source of volcanism. The latter, in all likelihood, explains the existence of the Great Red Spot, which has been observed since the 17th century. If there is a semi-liquid or solid core on the planet, there must be a strong greenhouse effect.
According to some scientists, Jupiter plays the role of a kind of “vacuum cleaner” in the solar system - its powerful magnetic-gravitational field intercepts comets, asteroids and other bodies wandering in the Universe. A clear example was the capture and fall of the comet Shoemaker-Levy 9 onto Jupiter in 1994. The force of gravity turned out to be so strong that the comet split into separate fragments, which crashed into the atmosphere of Jupiter at a speed of over 200 thousand km/h. Each explosion reached millions of megatons of power, and observers from Earth saw explosion stains and diverging waves of excited atmosphere.
At the beginning of 2003, the number of Jupiter's satellites reached 48, a third of which have their own names. Many of them are characterized by reverse rotation and small sizes - from 2 to 4 km. The four largest satellites - Ganymede, Callisto, Io, Europa - are called Galileans. The satellites are composed of hard stone material, apparently of silicate composition. Active volcanoes, traces of ice and, possibly, liquids, including water, were found on them.
Saturn, The “ringed” planet is no less interesting. Its average density, calculated from the apparent radius, is very low - 0.69 g/cm 3 (without atmosphere - about 5.85 g/cm 3). The thickness of the atmospheric layer is estimated at 37-40 thousand km. A distinctive feature of Saturn is its ring located above the cloud layer of the atmosphere. Its diameter is 274 thousand km, which is almost twice the diameter of the planet, and its thickness is about 2 km. Based on observations from space stations, it has been established that the ring consists of a number of small rings located at different distances from each other. The substance of the rings is represented by solid fragments, apparently silicate rocks and ice blocks ranging in size from a speck of dust to several meters. Atmospheric pressure on Saturn is 1.5 times higher than on Earth, and the average surface temperature is about -180°C. The planet's magnetic field is almost half as strong as the Earth's, and its polarity is opposite to the polarity of the Earth's field.
30 satellites have been discovered near Saturn (as of 2002). The most distant of them, Phoebe (diameter about km) is located 13 million km from the planet and revolves around it in 550 days. The closest one is Mimas (diameter 195 km) located at 185.4 thousand km and makes a full revolution in 2266 hours. The mystery is the presence of hydrocarbons on the satellites of Saturn, and possibly on the planet itself.
Uranus. The axis of rotation of Uranus is located almost in the plane of its orbit. The planet has a magnetic field, the polarity of which is opposite to that of the Earth, and the intensity is less than that of the Earth.
In the dense atmosphere of Uranus, whose thickness is 8500 km, ring formations, spots, vortices, and jet streams have been discovered, which indicates a restless circulation of air masses. The wind directions generally coincide with the rotation of the planet, but at high latitudes their speed increases. The greenish-blue color of the cold atmosphere of Uranus may be due to the presence of [OH - ] radicals. The helium content in the atmosphere reaches 15%; methane clouds have been found in the lower layers.
Around the planet, 10 rings ranging in width from several hundred meters to several kilometers, consisting of particles about 1 m in diameter, were discovered. Moving inside the rings are stone blocks of irregular shape and a diameter of 16-24 km, called “shepherd” satellites (probably asteroids).
Among the 20 satellites of Uranus, five stand out for their significant sizes (from 1580 to 470 km in diameter), the rest are less than 100 km. They all look like asteroids captured by the gravitational field of Uranus. On the spherical surface of some of them, giant linear stripes were noticed - cracks, possibly traces of glancing impacts of meteorites.
Neptune- the most distant planet from the Sun. Atmospheric clouds are formed mainly by methane. In the upper layers of the atmosphere there are wind currents rushing at supersonic speeds. This means the existence of temperature and pressure gradients in the atmosphere, apparently caused by the internal heating of the planet.
Neptune has 8 rocky satellites, three of which are of significant size: Triton (diameter 2700 km), Nerida (340 km) and Proteus (400 km), the rest are smaller - from 50 to 190 km.
Pluto- the most distant of the planets, discovered in 1930, does not belong to the giant planets. Its mass is 10 times less than the earth's.
Rotating rapidly around its axis, Pluto has a highly elongated elliptical orbit, and therefore from 1969 to 2009 it will be closer to the Sun than Neptune. This fact may be additional evidence of its “non-planetary” nature. It is likely that Pluto belongs to bodies from the Kuiper belt, discovered in the 90s of the 20th century, which is an analogue of the asteroid belt, but beyond the orbit of Neptune. Currently, about 40 such bodies with a diameter of 100 to 500 km, very dim and almost black, with an albedo of 0.01 - 0.02 (the Moon's albedo is 0.05) have been discovered. Pluto may be one of them. The surface of the planet is obviously icy. Pluto has a single satellite, Charon, with a diameter of 1190 km, with an orbit passing 19 thousand km from it and an orbital period of 6.4 Earth days.
Based on the nature of the movement of the planet Pluto, researchers suggest the presence of another extremely distant and small (tenth) planet. At the end of 1996, it was reported that astronomers from the Hawaiian Observatory had discovered a celestial body consisting of ice blocks that rotates in a near-solar orbit beyond Pluto. This minor planet does not yet have a name and is registered under the number 1996TL66.
Moon- a satellite of the Earth, rotating from it at a distance of 384 thousand km, whose size and structure bring it closer to the planets. The periods of axial and sidereal rotation around the Earth are almost equal (see Table 3.1), which is why the Moon always faces us with one side. The appearance of the Moon for an earthly observer is constantly changing in accordance with its phases - new moon, first quarter, full moon, last quarter. The period of complete change of lunar phases is called synodic month, which on average is equal to 29.53 Earth days. It doesn't match sidereal(to the stars) month constituting 27.32 days, during which the Moon makes a full revolution around the Earth and at the same time - a revolution around its axis in relation to the Sun. During the new moon, the Moon is between the Earth and the Sun and is not visible from the Earth. During a full moon, the Earth is between the Moon and the Sun and the Moon is visible as a full disk. Associated with the positions of the Sun, Earth and Moon solar And lunar eclipses- positions of the luminaries at which the shadow cast by the Moon falls on the surface of the Earth (solar eclipse), or the shadow cast by the Earth falls on the surface of the Moon (lunar eclipse).
The lunar surface is an alternation of dark areas - “seas”, corresponding to flat plains, and light areas - “continents”, formed by hills. The height differences reach 12-13 km, the highest peaks (up to 8 km) are located near the South Pole. Numerous craters ranging in size from several meters to hundreds of kilometers are of meteorite or volcanic origin (in the Alphonse crater, the glow of the central mountain and the release of carbon were discovered in 1958). Intense volcanic processes characteristic of the Moon in the early stages of development are now weakened.
Samples of the upper layer of lunar soil - regolith, taken by Soviet spacecraft and American astronauts, showed that igneous rocks of basic composition - basalts and anorthosites - emerge on the surface of the Moon. The former are characteristic of “seas”, the latter - of “continents”. The low density of regolith (0.8-1.5 g/cm3) is explained by its high porosity (up to 50%). The average density of the darker “marine” basalts is 3.9 g/cm3, and the lighter “continental” anorthosites is 2.9 g/cm3, which is higher than the average density of crustal rocks (2.67 g/cm3) . The average density of the Moon's rocks (3.34 g/cm3) is lower than the average density of the Earth's rocks (5.52 g/cm3). They assume a homogeneous structure of its interior and, apparently, the absence of a significant metallic core. Up to a depth of 60 km, the lunar crust is composed of the same rocks as the surface. The Moon has not detected its own dipole magnetic field.
In terms of chemical composition, lunar rocks are close to those on Earth and are characterized by the following indicators (%): SiO 2 - 49.1 - 46.1; MgO - 6.6-7.0; FeO - 12.1-2.5; A1 2 O 3 - 14.7-22.3; CaO -12.9-18.3; Na 2 O - 0.6-0.7; TiO 2 - 3.5-0.1 (the first numbers are for the soil of the lunar “seas”, the second - for continental soil). The close similarity of the rocks of the Earth and the Moon may indicate that both celestial bodies were formed at a relatively short distance from each other. The Moon formed in a near-Earth “satellite swarm” approximately 4.66 billion years ago. The bulk of iron and fusible elements at this time had already been captured by the Earth, which probably determined the absence of an iron core on the Moon.
Its small mass allows the Moon to retain only a very rarefied atmosphere consisting of helium and argon. Atmospheric pressure on the Moon is 10 -7 atm during the day and ~10 -9 atm at night. The absence of an atmosphere determines large daily fluctuations in surface temperature - from -130 to 180C.
Exploration of the Moon began on January 2, 1959, when the first Soviet automatic station, Luna-1, launched towards the Moon. The first humans were American astronauts Neil Armstrong and Edwin Aldrin, who landed on the moon on July 21, 1969 on the Apollo 11 spacecraft.
Earth as a planet Earth's place in the Universe The Earth is part of the Universe, it experiences a powerful cosmic influence. The Universe is the entire world, limitless in time and space, which consists of many cosmic bodies that form systems of varying complexity - from giant galaxies, including billions of stars, to planets with satellites. The solar system is located in one of many billions of galaxies - our Galaxy. The Galaxy includes more than 100 billion stars, interstellar matter and diffuse nebulae. She owns all the stars that we observe.
Our Galaxy is strongly flattened and, edge-on, should be visible in the shape of a biconvex lens with spiral branches extending from the center. In the plane of greatest extension and rotation* of the Galaxy, the maximum number of stars is crowded together, which, due to their distance, are indistinguishable individually and merge in the sky into a light stripe called the Milky Way. The age of the Galaxy is estimated at approximately 12 billion years. Our eye distinguishes other galaxies in the starry sky in the form of light, foggy spots - nebulae. In addition to galaxy nebulae, other nebulae are visible in the starry sky - accumulations of luminous gas or dust. Dust nebulae glow from the reflected light of nearby large stars. * The galaxy makes a complete revolution in ≈200 million years (galactic year)
The closest giant spiral star system to us is the Andromeda Nebula. It is similar in type and structure to our Galaxy, but is 1.5 times larger in size and consists of tens of billions of stars. This galaxy can be observed with the naked eye at mid-latitudes in the northern hemisphere. In the constellation Andromeda, it is visible as a tiny, oval, faintly luminous cloud. We see the Andromeda nebula as it was more than two million years ago: for so long a ray of light has been coming to us from this closest star system. Galaxy in the constellation Andromeda
About 98% of cosmic matter is contained in stars. Stars are red-hot luminous rotating gas (plasma) balls. They consist of hydrogen and helium and differ in temperature, size, mass, density, radiation power, color, brightness, luminosity, etc. Light rays passing through the atmosphere are weakened due to absorption, refracted, and change color. The atmosphere is never calm, so the celestial bodies seem to flicker to us, and in color photographs they turn out to be of different colors, which do not depend on the actual radiation of the star itself. The location of stars in the Universe changes extremely slowly, so the configuration of the constellations is relatively stable. For thousands of years, the relative position of the stars has hardly been disturbed and they are easy to find in the sky using star maps, which show 88 constellations (by decision of the General Assembly of the International Astronomical Union, held in Rome in 1922).
Starry sky map In the center is the North Pole of the World. The main lines are drawn on the celestial coordinate grid: the celestial equator, celestial meridians, daily parallels, the ecliptic, by which the coordinates of the luminaries are determined - the declination and right ascension of the stars and the Sun
a(alpha) – right ascension of the luminary: the arc of the celestial equator, which is measured from the point of the vernal equinox (- gamma) to the circle of declination of the luminary (RM) in the direction opposite to the rotation of the celestial sphere; (delta) – declination of the luminary: arc of the circle of declination from the equator to the luminary
A landmark of the starry sky of the northern hemisphere is the North Star, the closest bright luminary to the North Pole of the world. Its diameter is 120 times the solar diameter. It is a double star with a companion slightly larger than the Sun. It pulsates, changing its volume and brilliance. The North Star in our era is close to the North Pole of the world. Its declination is 89 17΄. In aviation, navigation, and astronautics, the location and course of an airplane, ship, or spacecraft is determined using the so-called navigation stars. Their location in the sky has been determined extremely accurately, and tables of their altitudes and azimuths have been compiled. Of more than 6,000 stars visible to the naked eye, there are only 26 such stars. In the northern hemisphere these are the Polar Star Arcturus, Vega, Capella, etc., in the southern hemisphere - Canopus, Peacock, Mimosa, etc. In the Southern Hemisphere, the navigation constellation is the Southern Cross. Its long crossbar almost exactly points to the South Pole of the world - the barely visible star Sigma (σ) in the constellation Octant, whose declination is 89 34΄. The navigators who pave the way for ships know all the navigation stars by heart.
In our time, the northern side of the horizon is determined by the Polar Star, as well as in the northern hemisphere the geographic latitude of a place, which is approximately equal to the height of the celestial pole above the horizon. The special role of the guiding North Star is still temporary. Due to the very slow cone-shaped movement of the earth's axis (a full revolution in ≈ 26,000 years), the North Pole of the world continuously wanders among the stars. About 3 thousand years ago, the star closest to the pole was Kohab (from Arabic - “Star of the North”) in the same constellation Ursa Minor. In 13 thousand years, the place of the North Star will be replaced by the star Vega in the constellation Lyra. The distance from the Earth to the North Star is such that a ray of light leaving it reaches our planet after 472 years. This means that we see the North Star as it was shortly after Magellan's circumnavigation of the world. If something happens to her now, we will find out about it in 472 years. Maybe it no longer exists, but it still shines in our sky.
The North Star is easy to find in the sky using the well-known constellation Ursa Major. Through the two outermost stars in his bucket you need to draw a straight line upward, on which you need to mark five times the distance between these stars. This is how we find the Ursa Minor ladle and find ourselves on the outermost star of the handle of its small ladle. This is the North Star.
One of the stars of our Galaxy is the Sun. This is a star belonging to the group of yellow dwarfs. Its diameter is 1,391,980 km, mass is 1.989 x 1030 kg (99.87% of the total mass of the entire Solar System), the sidereal (stellar) period of axial rotation (solar day) at the equator is 25.38 Earth days, at the poles ≈ 20 days, surface temperature – 5,807 K, age – about 5 billion years. The sun illuminates and warms the Earth, provides energy for processes occurring on its surface, and supports the “unquenchable fire” of life. One of the many conditions for the existence of life on our planet is the fact that the Sun is a relatively calm star, its radiation does not experience sharp fluctuations, although on average, after 11 years, periods of “active” Sun are observed, alternating with periods of “quiet” Sun.
People have long noticed that changes in the Sun (the appearance of so-called sunspots) affect nature and well-being. The brilliant Soviet natural scientist A.L. Chizhevsky (1897 -1964) devoted his life to the study of solar-terrestrial connections, who laid the foundations of heliobiology - the science of the influence of the Sun on living organisms. He wrote: “People and all earthly creatures are truly “children of the Sun.” He authored a large number of works on this topic, based on experiments and observations. The most famous of them is “The Terrestrial Echo of Solar Storms,” written in an interesting and understandable way for a wide range of readers and containing a huge amount of factual material, generalizations, theoretical conclusions and practical recommendations. Chizhevsky is called the “Leonardo of the twentieth century”, highly appreciating the breadth of his scientific thinking and contribution to world science. Shortly before his death, wonderful words were spoken to him: “. . . Modern dialectics teaches that any phenomenon can be understood only in its connection with the surrounding world. In the age of space, science must understand more and more deeply the mechanisms of connections between the Sun and living nature.”
The Sun is the evolutionary, dynamic and physical center of the Solar System. Possessing enormous mass and powerful gravity, it controls the movement of planets and other bodies of the system, except for the satellites of the planets. They revolve around their planets, since their attraction, due to their proximity, turns out to be stronger than the solar one. The solar system is a “family” of celestial bodies connected by forces of mutual attraction. Its center is a star called the Sun. The Solar System also undoubtedly includes 8 classical planets (Mercury, Venus, Earth, Mars (terrestrial planets), Jupiter, Saturn, Uranus, Neptune (giant planets), satellites of planets (there are more than 60 of them), small planets - asteroids, (over 5 thousand), hundreds of comets and many meteoroids. Until recently, the orbit of Pluto, the most “extreme” in the system (5.9 billion km or 39.5 AU), was taken as the boundary of the solar system.
1. astronomical unit is equal to the average distance of the Earth from the Sun - 149.6 million km 2. light year is equal to the distance that light travels in a vacuum, without being influenced by gravitational fields, in one Julian year 3. parsec - the distance corresponding to the reciprocal of the annual parallax (the apparent displacement of luminaries on the celestial sphere associated with the movement of the observer along with the Earth in orbit around the Sun); parallax 0.1 ״ corresponds to 10 parsecs (206265 AU or 30.857 x 10,000,000 km;
However, there has been constant debate about the status of Pluto for a long time: in size and properties it more closely resembles the satellites of planets, its orbit in shape and parameters differs from other planets. Recently, the General Assembly of Division III of the International Astronomical Union (IAU) decided to deprive Pluto of its “full-fledged planet” status on the grounds that otherwise it would have to assign such status to several more celestial bodies that deserve it no less than Pluto. This would upset many ideas about the solar system. It is easier to reduce the number of planets per object than to add several new ones. Accordingly, the boundary of the solar system shifts.
The great planetographic discovery of the late twentieth century - the discovery of the outer asteroid belt beyond the orbit of Neptune - significantly changed the understanding of the Solar System. A new look has emerged at the structure of the planetary system, which previously seemed not entirely harmonious, since it contained a “strange” planet - Pluto. . . So Pluto would have been an “outcast” of the solar system if in recent years (since 1992) it had not found worthy company: a completely new third type of planetary body - icy planets. . The “shock five-year period” was the period from 1999 to 2003, during which ≈ 800 previously unknown bodies were discovered. As a result, Pluto became just one of the objects in the outer asteroid belt, the so-called Kuiper belt. About 1,000 asteroids from this belt are now known, with the ten largest having a diameter exceeding 1,000 km. Here are the names of some of them: 2003 UB 313 (diameter 2800 km), Pluto (2390 km), 2005 FY 9 (1600 km), etc. The farthest object was Sedna (1500 km), which is 90 times farther from the Sun, than the Earth. The largest planetoid has not yet been given a name. A group of American astronomers, led by Michael Brown, proposed naming the “asteroid giant” Persephone, the name of Pluto’s wife in Greek mythology. Georgy Burba. Icy satellites of the Sun. J. Around the World, 2006 No. 12
The planets move slowly against the background of the zodiacal constellations as the Earth moves through its orbit. Over the course of a year, they travel from one constellation to another, so they can be visually distinguished from stars. The planet itself received its name precisely because of this feature (translated from Greek αstër ρlanëtës - wandering star). The movement of the planets in their orbits occurs from west to east, but the apparent movement across the sky occurs from east to west due to the rapid axial rotation of the Earth. As a result of the combination of the annual movement of the Earth and the planets in their orbits, all the planets describe loops against the background of the starry sky, performing either forward or backward movement. This phenomenon was noticed and correctly explained by N. Copernicus. The fact that the planets do not simply move back and forth, but describe loops, occurs because the planes of their orbits do not coincide with the plane of the Earth’s orbit.
Planets and their satellites (if, of course, they are visible from Earth) seem to us, just like stars, as more or less bright points. They shine with light reflected from the Sun. However, the Earth's satellite, the Moon, is 10,000 times brighter than the brightest star in the sky, Sirius, since it is immeasurably closer to the Earth. Since the position of the planets in the sky is constantly changing, they are not shown on the star map. To determine which planet we are observing, it is necessary to have special information, which is sometimes placed in calendars. There is another way to distinguish a planet from a star in the sky: you need to look at the star through binoculars. The planet is visible as a tiny disk, the star as a bright twinkling point. People with keen eyesight can get the same effect by viewing a light through a narrow hole, such as a loosely clenched fist. On a clear, dark night, against the backdrop of stars moving slowly across the sky without changing their relative positions, you can see with the naked eye bright, fairly quickly moving points - these are artificial satellites of the Earth. The brightest artificial object in low-Earth orbit was the Soviet automatic station Mir. It made 75,000 revolutions around the Earth during the 13 years of its existence. Her “splashdown” in the Pacific Ocean occurred on March 2, 1999.
The Earth has 6 celestial brothers (Mercury, Mars, Jupiter, Saturn, Uranus, Neptune) and one sister - Venus (goddess of love and beauty). They have many common features that arose in the process of similar formation and further evolution. All planets in the solar system are spherical in shape. They all revolve around the Sun in the same direction - counterclockwise for an observer looking from the North Pole. This direction is usually called direct. Almost all the satellites of the planets move in the same direction. The axial rotation of most planets occurs in the same direction. The exceptions are Venus and Uranus, which also rotates as if “lying down”: its axis lies almost in the orbital plane. The orbits of the planets are ellipses close to a circle, with the exception of Mercury. Because of this, the planets do not come close to each other and their gravitational interaction is small. The orbits of all planets are approximately in the same plane, close to the plane of the solar equator. The gaps between the orbits of planets naturally increase with distance from the Sun: each subsequent planet is 2 times further from the Sun than the previous one (the so-called law of planetary distances). All planets and their satellites have a shell structure, that is, they consist of concentric spheres that differ in the composition and structure of matter. They all move against the background of constellations. All planets shine by reflected sunlight. All planets are divided into two groups: small ones like Earth and giants like Jupiter. These differences are due to a large extent to different distances from the Sun, which affected both their physicochemical properties and dynamic features.
Each planet can “boast” of some kind of record. Mercury is the closest to the Sun, the smallest and hottest, almost devoid of an atmosphere, with the highest orbital speed (≈48 km/s) and the shortest year of 0.24 Earth years. Venus is the slowest rotating around its axis (≈ 243 days) in the direction opposite to its movement around the Sun. Earth is a double Earth-Moon planet, and only it has life. Mars has the highest mountains (the Olympus volcanic cone is higher than 25 km). Jupiter is the largest in mass and volume and the fastest rotating (9 hours 55 m) with the largest satellite (Ganymede). Saturn is the most oblate with a large polar compression (1/10), has the most magnificent rings and the largest number of satellites (according to the latest data - 22). Uranus - moves in orbit “lying on its side,” even slightly “upside down” (the inclination of the rotation axis is 98). Neptune - has the longest period of revolution around the Sun, has broken rings in the form of arcs (arches). Many planets have satellites. The largest satellite of Jupiter in the Solar System is Ganymede (one of its 16 “moons”). Its radius is 2631 km (larger than Mercury and Pluto), and its weight is more than two times that of the Moon. It is located at a distance of 1.07 million km from Jupiter and has a mixed silicate-ice composition. From above, the surface of Ganymede is covered with a layer of rock-ice dust several meters thick. There are many meteorite craters on the surface. Large satellites also include Saturn's Titan (radius ≈ 2580 km); Callisto (≈ 2350 km), Io (≈ 1815 km), Europa (≈ 1569 km) of Jupiter. The last three satellites and Ganymede were discovered by G. Galileo.
This is how the science fiction writers, the Strugatsky brothers (one of them is an astronomer), imagine the view of the sky on one of Jupiter’s satellites. The story takes place in the distant future at a scientific station located on one of the satellites of Jupiter." . . Amalthea, the fifth and closest satellite of Jupiter, completes a revolution on its axis in approximately thirty-five hours. In addition, in twelve hours it makes a complete revolution around Jupiter. Therefore, Jupiter creeps out from behind the close horizon every thirteen and a half hours. Jupiter rising is very beautiful. You just need to take the elevator in advance to the top floor under a transparent spectrolite cap. The sky is black, and there are many bright, unblinking stars on it. From the glare of the stars, vague reflections lie on the plain, and the rocky ridge appears as a deep black shadow in the starry sky. If you look closely, you can even make out the outlines of individual jagged peaks. It happens that the spotted sickle of Ganymede, or the silver disk of Callisto, or both, hangs low over the ridge, although this is quite rare. Then, from the peaks, smooth gray shadows stretch across the shimmering ice across the entire plain. And when the Sun is a round speck of blinding flame above the horizon, the plain turns blue, the shadows become black and every crack in the ice is visible. The coal blots on the rocket launch site look like huge puddles covered in ice. This evokes warm, half-forgotten associations, and you want to run to the field and walk on the thin ice crust to watch how it crunches under the magnetic shoe and wrinkles run along it, similar to foam in hot milk, only dark. But all this can be seen not only on Amalthea. For some reason, it is believed that brown color is ugly. This is what someone who has never seen a brown glow across half the sky and a clear red disk on it thinks so. Then the disk disappears. Only Jupiter remains, huge, brown, shaggy, it takes a long time to emerge from the horizon, as if swelling, and occupies a quarter of the sky. It is crossed obliquely by black and green stripes of ammonia clouds, and sometimes tiny white dots appear and immediately disappear on it - this is what exospheric prominences look like from Amalthea. . The director took one last look at the brown, blurry dome of Jupiter and thought that it would be nice to catch the moment when all four large satellites hang above the horizon - reddish Io, Europa, Ganymede and Callisto, and Jupiter itself in the first quarter is half orange, half brown. Then he thought that he had never seen the sunset. This should also be beautiful: the glow of the exosphere slowly fades, and one after another the stars flash in the blackening sky, like diamond needles on velvet. But usually the time of entry is the height of the working day.” . . Arkady Strugatsky, Boris Strugatsky. The path to Amalthea.
The only natural satellite of the Earth and another luminary on the celestial sphere is the Moon (in Greek mythology, the goddess of the Moon is Selene). It is located only 384,000 km from the Earth, its radius is only ≈ 4 times less than the Earth's (1738 km), and its mass is 81.5 times less than the mass of the Earth. In relation to its planet, until recently the Moon was considered the most massive satellite in the Solar System, therefore having the greatest influence on the main planet. In 1978, Pluto's satellite Charon was discovered, and now it holds this championship. Although Pluto itself is now considered a dwarf planet, it is still the planet with the most massive satellite. The Earth and the Moon are connected by a powerful mutual attraction and rotate as a single whole around a common center of gravity (barycenter) from west to east. The barycenter is located inside the Earth at a distance of 4750 km from its center, which is 0.73 Earth radii. Earth is often called a double planet. The Earth-Moon system completes a full revolution in 27.3 days. This is the so-called sidereal (from Latin sidus, gender sideris, that is, sidereal) month. It is the barycenter that moves in orbit around the Sun. The Earth and the Moon can also be called a double planet from another position. Of all the hypotheses for the formation of the Moon, many selenologists currently consider the model proposed by the Russian researcher E. L. Ruskol to be the most acceptable. She developed a theory of the joint formation of the Earth and the Moon as a double planet from a cloud of preplanetary bodies surrounding the Sun.
The Moon completes a full revolution around the Earth in 27.3 days relative to the stars (this is a sidereal, i.e., sidereal month) with an angular velocity of 13.2 per day. During the same time, it makes one revolution around its imaginary axis with the same angular velocity. Therefore, the Moon always faces the Earth with the same hemisphere. But it was not always so. Billions of years ago, the Moon was closer to the Earth and rotated around its axis faster than it orbited the Earth. Gradually, under the influence of the Earth's gravity, the Moon's rotation slowed down until both movements became synchronous. However, we now see ≈59% of the surface of our satellite due to the so-called libration (apparent wobble) for a number of reasons. Firstly, the Moon, according to Kepler’s second law, moves unevenly along its elliptical orbit - near the apogee (far point) slower than near perigee (near point), and “looks” at the center of the ellipse, and the Earth is at one of its foci. Therefore, we look beyond the sides of the lunar disk, sometimes from the west, sometimes from the east (optical libration along longitude). Secondly, due to the fact that the orbital planes of the Earth and the Moon do not coincide (the angle between them is > 5) and the axis of rotation of the Moon is inclined to the plane of its orbit by ≈ 83, it periodically turns towards us either the southern or the northern side. In this case, the circumpolar regions open slightly (optical libration in latitude). Thanks to the flights towards our satellite of the Soviet automatic interplanetary stations “Luna”, people from the Earth were able to look at the far side of the Moon. The Luna-9 station (1966) transmitted to Earth a circular panorama of the lunar landscape and, having successfully made a soft landing on the surface of the Moon, confirmed assumptions about its fairly solid soil and the absence of dust. This became an extremely important and reliable circumstance in the future for Soviet lunar rovers and American astronauts.
A remarkable feature of the surface not only of the Moon, but also of all the terrestrial planets is ring structures. Such structures on the Moon - craters, clearly visible from Earth, have different sizes: from small (less than a meter in diameter) to large (more than 200 km in diameter). Most of them have a more or less flat bottom and raised edges, and sometimes a hill-like elevation is visible in the center. Craters often form long chains stretching for hundreds of kilometers. Lunar craters have two origins. Some of the large craters are apparently volcanic, formed in the past when tectonic processes on the Moon were active. It should be taken into account that internal forces on the Moon worked with greater effect than on Earth due to the lower (6 times) gravity there. Now the Moon is a tectonically lifeless body, moonquakes are rare and weak. Most of the craters, according to the generally accepted opinion of selenologists, (Selena is the Moon) are of meteorite origin, that is, formed by the fall of large meteorites, asteroids, and comet nuclei. In the absence of an atmosphere slowing down their fall, they have a large shock-explosive force, as a result of which the main large craters are created, and secondary smaller ones in their vicinity could arise from the fall of stones scattered from the impact.
The pristine relief of the Moon is, as it were, “preserved”, not destroyed due to the absence of an atmosphere and hydrosphere, as well as due to the action of the “solar wind” - corpuscular flows (elementary particles flying from the Sun), which cause sintering of the surface layer and its transformation into a relatively strong spongy crust (rigolith). This also inhibits slope landslide processes. On Earth, the primary cratered relief is greatly destroyed by all slope and other relief-forming processes and is therefore veiled, although it can be traced both in a buried form and on the surface of the planet. There are approximately 300,000 craters on the visible side of the Moon with a diameter of more than a kilometer. Some of them have names: Copernicus, Kepler, Tycho, etc. In addition to craters on the Moon, there are vast dark, flat areas - the so-called “seas”, but without water (Ocean of Storms, Sea of Rains, etc.), and light mountainous areas - so called "continents". Many seas are bordered by long mountain ranges named after the earth's mountains - the Alps, the Caucasus, the Pyrenees, etc.
Asteroids are small bodies of the Solar System. The main asteroid belt lies between the orbits of Mars and Jupiter. According to the law of planetary distances, astronomers in the 18th century. They hoped to find an Earth-type planet here, but they discovered it at the beginning of the 19th century. a number of small planets: Ceres (diameter 1003 km), Pallas, Juno, etc. About 6000 asteroids are now known. Almost all of them move in a forward direction around the Sun at a speed of ≈ 20 km/s in elliptical orbits, with most of their orbits lying in the ecliptic plane. Some of them cross the Earth's orbit. Asteroids vary in size. About 30 have a diameter >200 km. The shape is irregular, multifaceted, angular and smoothed with numerous craters. The composition is different. They come in stone and metal. Asteroids are the main source of meteorites. In 1989, an asteroid ≈ 300 m in size flew at a distance of ≈ 650 thousand km from Earth. At the beginning of June 2006, an asteroid up to 900 m long flew at the closest possible distance from the Earth, slightly further than the Moon. An encounter with such a “pebble” would instantly change the climate and, in general, all life on Earth. If it fell into the ocean, waves tens of meters high would arise, which would wash away many coastal countries. Billions of tons of water vapor would be released into the atmosphere. . . If it fell on land, a huge amount of dust and smoke from the resulting fires would enter the air, which would cause a global climatic aerosol catastrophe: a rapid, sharp and prolonged drop in temperature to negative values. There is an assumption that the fall of a large asteroid in the Gulf of Mexico region ≈ 65 million years ago caused the death of ≈ 95% of all living organisms on the planet, including dinosaurs. The last “killer asteroid” (2006) missed, the danger has passed for a while, but another “space terrorist” is expected to visit, so astronomers carefully monitor the trajectories of asteroids. At the same time, scientific research is being conducted and methods are being developed to destroy dangerous “visitors” on the closest approaches to the Earth.
Comets (from the Greek κοmëtës - long-haired) are small bodies of the Solar System with even less mass than asteroids. These are cold bodies that begin to glow only when approaching the Sun. The orbits of comets are highly elongated ellipses or even parabolas. The periods of revolution around the Sun vary greatly: from several years to thousands and even millions of years. If the comet moves in a parabola, it does not return to the solar system at all. Movement in orbits can be either forward or backward. The orbital planes lie at very different angles, forming a real tangled ball. The comet has a prominent head and tail. The head consists of a solid core and a gaseous environment - coma. The core is an ice conglomerate consisting of 80% water mixed with various gases: carbon dioxide, methane, ammonia, hydrogen, as well as rocky and ferrous particles. In these space icebergs with a temperature of 250 -260 C, organic substances, perhaps the first bricks from which life on Earth took shape, could have been preserved, just like in a refrigerator.
Comet nuclei are small: from several hundred meters to several kilometers (for example, the size of the famous Comet Halley in 1986 was 16 km x 8 km). When approaching the Sun, under the influence of heat, the ice sublimes and a gaseous environment is formed - a coma. As a result of the repulsive effect of light pressure and the solar wind, a luminous tail of the comet (sometimes more than one) appears from rarefied gases and the finest dust (“visible nothing”), rushing away from the comet in the direction opposite to the Sun at a speed of 500 -1000 km/s. The tails reach billions of kilometers in length and glow with a cold luminescent light. The core can lose 30-40 tons of matter every second! Each approach of a comet to the Sun is accompanied by an irreparable loss of mass. Therefore, in the end, the supply of gases and solid particles is exhausted, the core is destroyed, partially disintegrates, forming “space debris”, which can serve as a source of a stream of meteors and even meteor shower. In human memory, the Earth has not collided with comet nuclei (only with their fragments), but has repeatedly fallen into cometary tails (in 1910 it passed through the tail of Halley's comet). This does not pose any danger to people: although the tail contains poisonous gases (methane, cyanogen), they are very rarefied and their admixture in the atmosphere is imperceptible.
There is an assumption that the explosion in 1908 in the taiga in the Podkamennaya Tunguska basin, which we call the fall of the Tunguska meteorite (there was no meteorite there), was actually the result of a collision of the Earth with the nucleus of a small comet Encke with a diameter of about 30 m. When the nucleus fell almost everything evaporated due to heating in the dense layers of the atmosphere, and at an altitude of 5-10 km, due to enormous air pressure, an explosion occurred. A strong earthquake was noted, the centuries-old taiga was mowed down like a scythe over a huge area (40 km x 50 km). Within a radius of ≈ 30 km from the center of the explosion, trees were felled with their tops facing outward. The brilliance, visible from a distance of 500 km, exceeded the radiance of the Sun, and thunderclaps were heard a thousand kilometers from the crash site. At the moment the comet entered the Earth's atmosphere (this happened in the morning, when the Sun was in the eastern half of the sky), an unusual glow in the night sky was observed west of the explosion area throughout Western Siberia and Europe to the Atlantic. Perhaps it was the tail of a comet. In the following days, increased dust content was noticed in the Earth's atmosphere. The history of Comet Biela, named after the Czech Biela (Bely) who discovered it in 1826, is interesting. The orbital period of this comet was ≈ 7 years. It was observed twice, and the third time (in 1846), before the eyes of astronomers, it split into two parts. In 1852, both daughter comets appeared, but the distance between them increased. The next time conditions for observation appeared only in 1872, but the comet could not be detected. But on November 27, 1872, on the night when the Earth crossed the orbit of Biela, a heavy meteor shower was observed with a radiant from the Andromeda constellation, where, according to calculations, the comet should have been located. And even now, every year when the Earth crosses Biela’s orbit, an increased number of meteors is observed. Apparently the meteoric material of the comet was more or less evenly distributed throughout its orbit. This indicates that comets are short-lived celestial bodies.
In outer space, solid bodies of various sizes are present in abundance, from dust grains to blocks tens and hundreds of meters in size. Dust grains fall to the Earth every hour, and blocks - once every hundreds or thousands of years. Meteors are tiny solid particles weighing grams and fractions of a gram, invading the Earth's atmosphere at a speed of tens of kilometers per second. Due to friction with the air at an altitude of 80-100 km, they heat up to several thousand degrees Celsius, while glowing for 1-2 seconds, losing mass or spraying and disappearing before reaching the Earth's surface. Meteors leave behind ionized gases - a meteor trail, often visible to the naked eye. Meteors appear as "shooting stars" against the dark night sky. Meteors can be isolated, sporadic, or form meteor showers. Particularly abundant of them are called meteor showers. All particles of meteor showers move parallel to each other, but according to the laws of perspective, they seem to fly away from one point in the sky, called the radiant. Meteor showers are named after the constellations in which their radiants are located. There are 8 known flows. One of the most abundant is the “Persians” (according to the constellation Perseus). It lasts from August 5th to 18th with a peak around the 10th. At the end of the first ten days of October there are “draconids”, in the third ten days of October there are “Orionids”. Every 33 and a quarter years in mid-November a powerful stream returns to the Earth - the Leonids. So on the night of November 17, 1966, up to 2,300 meteors per minute were counted in the sky over Arizona. Meteor showers occur when a meteor swarm encounters the Earth - a cluster of meteor bodies that are products of the disintegration of comets, the crushing of asteroids, etc. Most large meteor bodies move like comets in elongated elliptical orbits. The orbits of the streams are carefully studied, because they can be dangerous for spacecraft.
Have you ever tried to indicate your universal address in letters? Its format could roughly follow the following template - house/street/city/country/planet Earth/Orion Arm/Milky Way Galaxy/Local Group of Galaxies/Virgo Supercluster/Universe.
In general, galaxies in our Universe are not evenly distributed - they form huge clusters, which in turn are part of even more gigantic superclusters, uniting hundreds of thousands of galaxies. Outwardly, these superclusters resemble some kind of gigantic networks, the threads of which are formed by clusters of galaxies. Like other galaxies in the Universe, our Milky Way must also be part of one of these megastructures.
But of course it's not that simple. Superclusters do not have any clear boundaries, which makes it quite difficult to determine their true sizes. But it is possible that thanks to the efforts of a group of astronomers, an article about which was published in today's issue of the journal Nature, our universal address can be clarified by adding one more position to it.
The Universe is expanding, which is manifested in the so-called. redshift. However, the gravity of galaxies located next to each other affects their speed and direction of movement. Using radio telescopes, researchers measured the location and speed of eight thousand galaxies. Thanks to this, they were able to create a map of “cosmic flows” - the peculiar “migration” paths of galaxies. As it turns out, the Milky Way is part of a huge supercluster, 520 million light years long, which includes over one hundred thousand galaxies. The newly discovered structure was named Laniakea - translated from Hawaiian - Vast skies.
The colors on the map indicate the distribution of galaxies. Red corresponds to areas with the highest density of galaxies, blue to relatively deserted areas. Of course, we must not forget that the galaxies we observe make up only a small percentage of the mass of the universe, while the bulk of it is dark matter, which we can detect only by indirect evidence.
The blue dot is the local cluster of galaxies located on the outskirts of Laniakea, where our Milky Way is located.
The white lines show the streams along which the Laniakea galaxies are moving towards the Great Attractor - a gravitational anomaly, located at a distance of 250 million light years from us. Unfortunately, we cannot observe the Great Attractor directly, since it is located in the “avoidance zone”, closed from observation by the plane of the Milky Way with a lot of dust. But we can measure the effect it has on the motion of galaxies. Apparently, the Attractor is a kind of core of Laniakea, towards which the galaxies that form it tend, like water flowing down a descending path into a valley.
The orange line shows the border of Laniakea. It can be roughly compared to a watershed - beyond its boundaries, cosmic flows change their direction and rush to the center of the neighboring superclusters Coma Berenices, Perseus-Pisces and Shapley.
In conclusion, I can only say that our Universe is truly huge and full of miracles, most of which we are not even aware of. I wonder how many even larger universal structures there are, of which Laniakea is an integral part?
Do you know that we are lucky to be born not only in the “life zone” of a star, but also in the entire galaxy?
What do other stars look like from the outside? We have already said, but how would an outside observer see our solar system and our Sun star?
Judging by the analysis of the surrounding space, the solar system is currently moving through the local, consisting mainly of hydrogen and some helium. It is assumed that this local interstellar cloud spreads over a distance of 30 light years, which in terms of kilometers is something like 180 million km.
In turn, “our” cloud is located inside an elongated gas cloud, the so-called local bubble, formed by particles of ancient supernovae. The bubble stretches over 300 light years and is located on the inner edge of one of the spiral arms.
However, as I said earlier, our exact position relative to the arms of the Milky Way is unknown to us - whatever one may say, we simply do not have the opportunity to look at it from the outside and assess the situation.
What to do: if almost anywhere on the planet you can determine your location with sufficient accuracy, then if you are dealing with galactic scales, this is impossible - our galaxy is 100 thousand light years across. Even when studying the outer space around us, much remains unclear.
If we use the intergalactic positioning system, we will probably find ourselves between the top and bottom of the Milky Way and halfway between the center and the outer edge of the galaxy. According to one hypothesis, we settled in a rather “prestigious area” of the galaxy.
There is an assumption that stars located at a certain distance from the center of the galaxy are in the so-called habitable zone, that is, where life is theoretically possible. And life is possible only in the right place with the right temperature - on a planet located at such a distance from the star that it has liquid water. Only then can life emerge and evolve. In general, the habitable zone extends 13 - 35 thousand years from the center of the Milky Way. Considering that our solar system is located 20 – 29 light years from the galactic core, we are right in the middle of the “life optimum”.
However, at present the Solar System is indeed a very quiet “region” of space. The planets of the system were formed long ago, the “wandering” planets either crashed into their neighbors or disappeared outside our stellar home, and the number of asteroids and meteorites has decreased significantly compared to the chaos that reigned around 4 billion years ago.
We believe that early stars formed only from hydrogen and helium. But since stars are a kind of star, heavier elements were formed over time. This is extremely important because when stars die and explode, . Their remains become building material for heavier elements and peculiar seeds of the galaxy. Where else would they come from, if not from the “smiths of chemical elements” located in the bowels of the stars?
For example, carbon in our cells, oxygen in our lungs, calcium in our bones, iron in our blood - all these are the same heavy elements.
The uninhabited zone apparently lacked the processes that made life possible on Earth. Closer to the edge of the galaxy, fewer massive stars exploded, meaning fewer heavy elements were ejected. Further in the galaxy you will not find atoms of such important elements for life as oxygen, carbon, nitrogen. The habitable zone is characterized by the presence of these heavier atoms, and beyond its boundaries life is simply impossible.
If the outermost part of the galaxy is a “bad area,” then its central part is even worse. And the closer to the galactic core, the more dangerous it is. In the time of Copernicus, we believed that we were at the center of the Universe. It seems that after everything we have learned about the heavens, we have decided that we are at the center of the galaxy. Now that we know even more, we understand how we can lucky be off center.
In the very center of the Milky Way there is an object of enormous mass - Sagittarius A, black hole about 14 million km across, its mass is 3700 times the mass of our Sun. The black hole at the center of the galaxy emits powerful radio emissions, enough to incinerate all known life forms. So it's impossible to get close to her. There are other regions of the galaxy that are uninhabitable. For example, due to the strongest radiation.
O-type stars- these are giants much hotter than the Sun, 10-15 times larger than it, and emitting colossal doses of ultraviolet radiation into space. Everything perishes under the rays of such a star. Such stars are capable of destroying planets before they even finish forming. The radiation from them is so great that it simply rips off matter from the forming planets and planetary systems, and literally rips planets out of orbit.
O-type stars are the real “death stars”. No life is possible within a radius of 10 or more light years from them.
So our corner of the galaxy is like a blooming garden between the desert and the ocean. We have all the elements necessary for life. In our area, the main barrier against cosmic rays is the magnetic field of the Sun, and the magnetic field of the Earth protects us against radiation from the Sun. The Sun's magnetic field is responsible for sunny wind, which is protection from the troubles that come to us from the edge of the solar system. The magnetic field of the Sun spins the solar wind, which is a charged stream of protons and electrons shooting out of the Sun at a speed of a million kilometers per hour.
The solar wind carries a magnetic field over a distance three times greater than the orbit of Neptune. But a billion kilometers later, in a place called heliopause, the solar wind dries up and almost disappears. Having slowed down, it ceases to be a barrier to cosmic rays from interstellar space. This place is the border heliosphere.
If there were no heliosphere, cosmic rays would penetrate our solar system unhindered. The heliosphere works like a cage for diving with sharks, only instead of sharks there is radiation, and instead of a scuba diver there is our planet.
Some of the cosmic rays do penetrate the barrier. But at the same time they lose most of their strength. We used to think that the heliosphere was an elegant barrier, something like a folded curtain of a magnetic field. Until data was received from Voyager 1 and Voyager 2, launched in 1997. At the beginning of the 21st century, data from the devices was processed. It turned out that the magnetic field at the boundary of the heliosphere is something like magnetic foam, each bubble of which is about 100 million km wide. We are used to thinking that the surface of the field is continuous, creating a reliable barrier. But, as it turned out, it consists of bubbles and patterns.
As we explore our galactic environs, dust and gas interfere with our ability to examine objects in more detail. Over a long history of observations, we have found out the following. When we examine the night sky with the naked eye or with a telescope, we see a lot in the visible part of the spectrum. But this is only part of what is actually there. Some telescopes can see through cosmic dust thanks to the infrared vision.
The stars are very hot, but are hidden in shells of dust. And we can observe them with an infrared telescope. Objects can be transparent or opaque, depending on the light waves, that is, the light that either can or cannot pass through them. If something like gas or cosmic dust gets between the object and the telescope, it can move to another part of the spectrum, where the light waves will have a different frequency. In this case, this obstacle may become visible.
Armed with infrared and other devices, we discovered many space neighbors around us whose existence we did not suspect. There are a number of instruments for observing cosmic bodies and stars in different parts of the spectrum.
Having discovered many new cosmic bodies around us, we wonder how they behave, how they influenced the Earth at the time of the origin of life on Earth. Some of them are “good neighbors,” that is, they behave predictably and move along a predictable trajectory. “Bad neighbors” are unpredictable. This could be an explosion of a dying star or a collision, the fragments of which will fly towards us.
Some of our neighbors in ancient times may have brought us a “gift” that changed everything. When our Earth finished forming and cooled, the surface was still very hot. And since the water simply evaporated, it could again be brought to Earth by numerous comets or asteroids. There are many theories about how we could get water.
According to one of them, water could have been brought by icy bodies that came into the solar system from outside or remained after the formation of the Sun and planets. According to one of the latest theories, about 4 million years ago, the gravity of the heavy gas giant Jupiter sent icy asteroids towards Mars, Earth and Venus. But only on Earth was ice able to penetrate into the mantle. Water softened the Earth and initiated the process of plate tectonics, resulting in the appearance of continents and oceans.
How did life originate in the oceans? Maybe the necessary organic compounds got into them from space? In some meteorites, which are called carbon dioxide melancholy, scientists have discovered organic compounds that could contribute to the development of life on Earth. These compounds are similar to those collected from Antarctic meteorites, interstellar dust samples and comet fragments obtained from stardust by NASA in 2005.
The origin of life is a long chain of reactions of organic compounds. All organic compounds contain carbon and it is possible that different circumstances led to the formation of different organic compounds. Some could form here on the planet, and others in space. It is quite possible that without these intergalactic gifts from our neighbors, life on Earth would never have appeared.
But there are also unpredictable neighbors. For example, the star is an orange dwarf Gliese 710. This star is 60% more massive than the Sun, is currently only 63 light-years from Earth and continues to approach the solar system.
The Oort Cloud is a huge sphere of frozen rocks and blocks of ice surrounding the Solar System (center). The source of comets and wandering meteorites “from outside” our system
Also at a distance of 1 light year from Earth there is the so-called Oort cloud. We can observe comets from the Oort cloud if they pass close enough to the Sun, but this is not usually the case and we do not see them.
There are also simply “strange neighbors”. One of them (or rather, a whole family) is the stars of the Centaurus constellation.
The star Alpha Centauri, the brightest star in the constellation Centaurus, is for us the third brightest star in the night sky. She is our closest neighbor, located 4 light years away from us. Until the 20th century, it was believed that this was a double star, but later it turned out that we are observing nothing more than a star system of three stars orbiting each other at once!
Alpha Centauri A is very similar to our Sun, and its mass is the same. Alpha Centauri B is slightly smaller, and the third star Proxima Centrauri is an M type star whose mass is about 12% of the mass of the Sun. It is so small that we cannot observe it with the naked eye.
It turns out that many of our other neighboring stars also have multiple systems. About 8.5 light years away, Sirius, known as one of the brightest stars in the sky, is also a double star. Most stars are smaller than our Sun and are often binaries. So our lone Sun is rather an exception to the rule.
Most of the stars around are red or brown dwarfs. Red dwarfs make up up to 70% of all stars not only in our galaxy, but also in the Universe. We are accustomed to our Sun, it seems to us a standard, but there are many more red dwarfs.
We weren't sure if there were brown dwarfs among our neighbors until 1990. These space objects are also unique - not quite stars, but not planets either, and their color is not brown at all.
Brown dwarfs are one of the most mysterious inhabitants of our solar system because they are indeed very cold and very dark. They emit little light, making them extremely difficult to observe. In 2011, one of NASA's Wide-Field Infrared Explorer telescopes, somewhere between 9 and 40 light-years from Earth, discovered many brown dwarfs with surface temperatures once thought impossible. Some of these brown dwarfs are so cool you can even touch them. Their surface temperature is only 26°C. Stars at room temperature—whatever you see in the universe!
However, outside our “local bubble” there are not only stars, but also planets, or rather exoplanets- that is, not revolving around the Sun. The discovery of such planets is an extremely difficult event. It's like watching one single light bulb in Las Vegas at night! In fact, we don’t even see these planets, but only guess about them when the Kepler Telescope, which monitors changes in the brightness of stars, records an insignificant change in the brightness of a star when one of the exoplanets passes across its disk.
As far as we know, our closest exoplanetary neighbor is literally “down the street” from us, “only” 10 light years away, orbiting the orange star Epsilon Eridani. However, the exoplanet is more like Jupiter than Earth, since it is a huge gas giant. However, considering that less than two decades have passed since the first discoveries of exoplanets, who knows what awaits us next.
In 2011, astronomers discovered a new type of planet in our area - homeless planets. It turns out that there are planets that do not orbit their parent star. They began their lives like all the other planets, but for one reason or another they were displaced from their orbit, left their solar systems and are now wandering aimlessly around the galaxy with no way to return home. This is surprising, but a new definition will be required to name this kind of planets, for planets that exist outside the gravitational pull of their parent stars.
However, there are a couple of events looming on the horizon that could become a real sensation even on a cosmic scale.
