On March 13, 1781, English astronomer William Herschel discovered the seventh planet of the solar system - Uranus. And on March 13, 1930, American astronomer Clyde Tombaugh discovered the ninth planet of the solar system - Pluto. By the beginning of the 21st century, it was believed that the solar system included nine planets. However, in 2006, the International Astronomical Union decided to strip Pluto of this status.
There are already 60 known natural satellites of Saturn, most of which were discovered using spacecraft. Most of the satellites consist of rocks and ice. The largest satellite, Titan, discovered in 1655 by Christiaan Huygens, is larger than the planet Mercury. The diameter of Titan is about 5200 km. Titan orbits Saturn every 16 days. Titan is the only moon to have a very dense atmosphere, 1.5 times larger than Earth's, consisting primarily of 90% nitrogen, with moderate methane content.
The International Astronomical Union officially recognized Pluto as a planet in May 1930. At that moment, it was assumed that its mass was comparable to the mass of the Earth, but later it was found that Pluto’s mass was almost 500 times less than the Earth’s, even less than the mass of the Moon. Pluto's mass is 1.2 x 10.22 kg (0.22 Earth's mass). Pluto's average distance from the Sun is 39.44 AU. (5.9 to 10 to 12 degrees km), radius is about 1.65 thousand km. The period of revolution around the Sun is 248.6 years, the period of rotation around its axis is 6.4 days. Pluto's composition is believed to include rock and ice; the planet has a thin atmosphere consisting of nitrogen, methane and carbon monoxide. Pluto has three moons: Charon, Hydra and Nix.
At the end of the 20th and beginning of the 21st centuries, many objects were discovered in the outer solar system. It has become obvious that Pluto is only one of the largest Kuiper Belt objects known to date. Moreover, at least one of the belt objects - Eris - is a larger body than Pluto and is 27% heavier. In this regard, the idea arose to no longer consider Pluto as a planet. On August 24, 2006, at the XXVI General Assembly of the International Astronomical Union (IAU), it was decided to henceforth call Pluto not a “planet”, but a “dwarf planet”.
At the conference, a new definition of a planet was developed, according to which planets are considered bodies that revolve around a star (and are not themselves a star), have a hydrostatically equilibrium shape and have “cleared” the area in the area of their orbit from other, smaller objects. Dwarf planets will be considered objects that orbit a star, have a hydrostatically equilibrium shape, but have not “cleared” the nearby space and are not satellites. Planets and dwarf planets are two different classes of objects in the Solar System. All other objects orbiting the Sun that are not satellites will be called small bodies of the Solar System.
Thus, since 2006, there have been eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The International Astronomical Union officially recognizes five dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris.
On June 11, 2008, the IAU announced the introduction of the concept of "plutoid". It was decided to call celestial bodies revolving around the Sun in an orbit whose radius is greater than the radius of Neptune’s orbit, whose mass is sufficient for gravitational forces to give them an almost spherical shape, and which do not clear the space around their orbit (that is, many small objects revolve around them) ).
Since it is still difficult to determine the shape and thus the relationship to the class of dwarf planets for such distant objects as plutoids, scientists recommended temporarily classifying all objects whose absolute asteroid magnitude (brilliance from a distance of one astronomical unit) is brighter than +1 as plutoids. If it later turns out that an object classified as a plutoid is not a dwarf planet, it will be deprived of this status, although the assigned name will be retained. The dwarf planets Pluto and Eris were classified as plutoids. In July 2008, Makemake was included in this category. On September 17, 2008, Haumea was added to the list.
The material was prepared based on information from open sources
The Earth, like all the planets in our Solar System, revolves around the Sun. And their moons revolve around the planets.
Since 2006, when it was transferred from the category of planets to dwarf planets, there are 8 planets in our system.
Planetary placement
All of them are located in almost circular orbits and rotate in the direction of rotation of the Sun itself, with the exception of Venus. Venus rotates in the opposite direction - from east to west, unlike Earth, which rotates from west to east, like most other planets.
However, the moving model of the solar system does not show so many small details. Among other oddities, it is worth noting that Uranus rotates almost lying on its side (the mobile model of the Solar System does not show this either), its rotation axis is tilted by approximately 90 degrees. This is associated with a cataclysm that occurred a long time ago and influenced the inclination of its axis. This could have been a collision with any large cosmic body that was unlucky enough to fly past the gas giant.
What groups of planets exist
The planetary model of the solar system in dynamics shows us 8 planets, which are divided into 2 types: terrestrial planets (these include: Mercury, Venus, Earth and Mars) and gas giant planets (Jupiter, Saturn, Uranus and Neptune).
This model does a good job of demonstrating the differences in planet sizes. Planets of the same group share similar characteristics, from structure to relative sizes; a detailed model of the Solar System in proportions clearly demonstrates this.
Belts of asteroids and icy comets
In addition to planets, our system contains hundreds of satellites (Jupiter alone has 62 of them), millions of asteroids and billions of comets. There is also an asteroid belt between the orbits of Mars and Jupiter, and the interactive Flash model of the Solar System clearly demonstrates it.
Kuiper Belt
The belt remains from the formation of the planetary system, and after the orbit of Neptune extends the Kuiper belt, which still hides dozens of icy bodies, some of which are even larger than Pluto.
And at a distance of 1-2 light years there is the Oort cloud, a truly gigantic sphere encircling the Sun and representing the remains of building material that was thrown out after the formation of the planetary system. The Oort cloud is so large that we are not able to show you its scale.
Regularly supplies us with long-period comets, which take about 100,000 years to reach the center of the system and delight us with their command. However, not all comets from the cloud survive their encounter with the Sun, and last year’s fiasco of comet ISON is clear evidence of this. It is a pity that this model of the flash system does not display such small objects as comets.
It would be wrong to ignore such an important group of celestial bodies, which were singled out into a separate taxonomy relatively recently, after the International Astronomical Union (MAC) held its famous session in 2006, in which the planet Pluto.
Background of the opening
And the prehistory began relatively recently, with the introduction of modern telescopes in the early 90s. In general, the beginning of the 90s was marked by a number of major technological breakthroughs.
Firstly, it was at this time that the Edwin Hubble Orbital Telescope was put into operation, which, with its 2.4 meter mirror placed outside the earth’s atmosphere, discovered an absolutely amazing world inaccessible to ground-based telescopes.
Secondly, the qualitative development of computer and various optical systems has allowed astronomers not only to build new telescopes, but also to significantly expand the capabilities of old ones. Through the use of digital cameras, which have completely replaced film. It became possible to accumulate light and keep track of almost every photon falling on the photodetector matrix with unattainable accuracy, and computer positioning and modern processing tools quickly moved such an advanced science as astronomy to a new stage of development.
Alarm bells
Thanks to these successes, it became possible to discover celestial bodies of quite large sizes beyond the orbit of Neptune. These were the first “bells”. The situation became greatly aggravated at the beginning of the 2000s; it was then that in 2003-2004 Sedna and Eris were discovered, which, according to preliminary calculations, had the same size as Pluto, and Eris was completely superior to it.
Astronomers have reached a dead end: either admit that they have discovered the 10th planet, or there is something wrong with Pluto. And new discoveries were not long in coming. In 2005, it was discovered that, together with Quaoar, discovered back in June 2002, Orcus and Varuna literally filled the trans-Neptunian space, which, beyond the orbit of Pluto, was previously considered almost empty.
International Astronomical Union
The International Astronomical Union, convened in 2006, decided that Pluto, Eris, Haumea and Ceres, which joined them, belong to. Objects that were in orbital resonance with Neptune in a ratio of 2:3 began to be called plutinos, and all other Kuiper Belt objects were called cubevanos. Since then, we have only 8 planets left.
The history of the formation of modern astronomical views
Schematic representation of the Solar system and spacecraft leaving its limits
Today, the heliocentric model of the solar system is an indisputable truth. But this was not always the case, until the Polish astronomer Nicolaus Copernicus proposed the idea (which was also expressed by Aristarchus) that it is not the Sun that revolves around the Earth, but vice versa. It should be remembered that some still think that Galileo created the first model of the solar system. But this is a fallacy; Galileo only spoke out in defense of Copernicus.
Copernicus' model of the solar system was not to everyone's taste, and many of his followers, such as the monk Giordano Bruno, were burned. But the model according to Ptolemy could not fully explain the observed celestial phenomena and the seeds of doubt in the minds of people had already been planted. For example, the geocentric model was not able to fully explain the uneven movement of celestial bodies, such as the retrograde movements of planets.
At different stages of history, there were many theories about the structure of our world. All of them were depicted in the form of drawings, diagrams, and models. However, time and the achievements of scientific and technological progress have put everything in its place. And the heliocentric mathematical model of the solar system is already an axiom.
The movement of the planets is now on the monitor screen
When immersed in astronomy as a science, it can be difficult for an unprepared person to imagine all aspects of the cosmic world order. Modeling is optimal for this. The online model of the Solar System appeared thanks to the development of computer technology.
Our planetary system has not been left without attention. Graphics specialists have developed a computer model of the Solar System with date entry, which is accessible to everyone. It is an interactive application that displays the movement of planets around the Sun. In addition, it shows how the largest satellites revolve around the planets. We can also see the zodiac constellations between Mars and Jupiter.
How to use the scheme
The movement of the planets and their satellites corresponds to their real daily and annual cycle. The model also takes into account relative angular velocities and initial conditions for the motion of space objects relative to each other. Therefore, at each moment of time their relative position corresponds to the real one.
An interactive model of the solar system allows you to navigate in time using a calendar, which is depicted as an outer circle. The arrow on it points to the current date. The speed of time can be changed by moving the slider in the upper left corner. It is also possible to enable the display of moon phases, in which the dynamics of the lunar phases will be displayed in the lower left corner.
Some assumptions
In recent years, something better than the parallactic method has been invented. Ways have been developed to send very short radio waves (microradio waves) of the type used in radars into outer space, where they are reflected from planets such as Venus, and then these reflected waves are received on Earth. The speed of propagation of radio waves is precisely known, and the time between the sending of the waves and their reception can also be measured very accurately. The distance covered by radio waves during a round trip, and therefore the distance to Venus at a given moment, can be determined with incomparably greater accuracy than the parallax method.
In 1961, it was studied how such microradio waves are reflected from Venus. Using the data obtained, it was calculated that the average distance from the Earth to the Sun is 149,573,000 km.
Using the Keplerian diagram of the structure of the solar system, it is possible to calculate the distances of all planets either from the Earth at a certain moment or from the Sun. It is more convenient to use the distance from the Sun, since it changes much less over time and not according to such complex laws as the distance from the Earth.
This distance can be expressed in one of the three most common units.
Firstly, it can be expressed in millions of kilometers. The kilometer is the most common unit for measuring long distances.
Secondly, to avoid numbers such as millions of kilometers, we can assume that the average distance from the Earth to the Sun is equal to one astronomical unit (abbreviated as “a, e.”) Then it will be possible to express the distances in a, e., with 1 a e. equal to 149,500,000 km. With quite sufficient accuracy we can assume that 1 a, e. is equal to 150,000,000 km.
Third, distance can be expressed in terms of the time it takes light (or any similar radiation, such as microradio waves) to travel. The speed of light in vacuum is 299,776 km/sec. For convenience, this number can be rounded to 300,000 km/sec.
Thus, a distance of approximately 300,000 km can be considered equal to one light second (for this is the distance covered by light in one second). A distance 60 times greater, or 18,000,000 km, is one light minute, and a distance another 60 times greater, i.e. 1,080,000,000 km is one light hour. We won't be too far wrong if we assume that a light hour is equal to one billion kilometers.
With this in mind, let us consider those planets that were known to the ancients and present a table of their average distances from the Sun, expressed in each of the three indicated units.
So, already since the time of Cassini, it has been known that the diameter of the solar system, limited by the orbit of Saturn, reaches almost 3 billion km. The diameter of the imaginary sphere that included the planets known to the ancient Greeks was not millions of kilometers, as the Greeks of Hipparchus believed, but thousands of millions.
But even this figure turned out to be an understatement. The diameter of the planetary system doubled at once in 1781, when the English astronomer, German by birth, William Herschel (1738-1822) discovered the planet Uranus. Then the diameter doubled again in two stages, when first the French astronomer Urban Joseph Le Verrier (1811-1877) discovered Neptune in 1846, then American astronomer Clyde William Tombaugh (born 1906) - Pluto in 1930.
The distances of these distant members of the solar system from the Sun are given below.
If we consider the orbit of Pluto, as we previously did the orbit of Saturn, we will see that the diameter of the solar system is not 3, but 12 billion kilometers. A ray of light that travels a distance equal to the circumference of the Earth in 1/7 sec and travels from the Earth to the Moon in 1 1/4 sec will take half a day to cross the solar system. Yes, since the times of the Greeks the sky has indeed moved into immeasurable distances.
Rice.
In addition, there is every reason to believe that it is not Pluto’s orbit that marks the border of the Sun’s domain. This does not mean that we should assume the existence of more distant planets that have not yet been discovered (although it is by no means impossible that such small and very distant planets actually exist). There are already known celestial bodies that are very easy to see from time to time and which, no doubt, move much further from the Sun than Pluto at the most distant point of its orbit. solar planet lunar eclipse
This fact was known even before the discovery of Uranus expanded the boundaries of the planetary part of the solar system itself. In 1684, the English scientist Isaac Newton (1642-1727) discovered the law of universal gravitation. This law strictly mathematically substantiated the Keplerian scheme of the structure of the solar system and made it possible to calculate the orbit of a body revolving around the Sun, even if the body was observed only in part of its orbit.
This, in turn, made it possible to tackle comets - “shaggy” luminous bodies that appeared in the sky from time to time. In ancient times and in the Middle Ages, astronomers believed that comets appear without any regularity and that their movement is not subject to any natural laws, while the broad masses were convinced that the only purpose of comets was to portend misfortune.
However, Newton's contemporary and friend, the English scientist Edmund Halley (1656-1742), tried to apply the law of gravity to comets. He noticed that some particularly bright comets appeared in the sky every 75-76 years. And in 1704, he suggested that all these comets were in fact the same celestial body, which moved around the Sun in a constant elliptical orbit, and an orbit so elongated that a significant part of it lay at a colossal distance from the Earth. When the comet was far from Earth, it was invisible. But every 75 or 76 years it would end up in the part of its orbit closest to the Sun (and Earth), and that's when it would become visible.
Halley calculated the orbit of this comet and predicted that it would return again in 1758. Indeed, the comet appeared that year (16 years after Halley's death) and has since been called Halley's Comet.
Rice.
At the point of its orbit closest to the Sun, Comet Halley is only about 90,000,000 km away from it, thus going slightly inside the orbit of Venus. At the most distant part of its orbit from the Sun, Comet Halley moves away from it approximately 3 1/2 times further than Saturn. At aphelion, the comet's distance from the Sun is 5,300,000,000 km; in other words, it goes far beyond the orbit of Neptune. Thus, by 1760, astronomers knew full well that the solar system was much larger than the Greeks thought, and they did not need to discover new planets to be convinced of this.
Moreover, Halley's comet is one of the comets relatively close to the Sun. There are comets that move around it in such incredibly elongated orbits that they return to it only once every few centuries, or even millennia. They move away from the Sun not by billions of kilometers, but most likely by hundreds of billions. Dutch astronomer Jan Hendrik Oort (born 1900) suggested in 1950 that there may be a whole huge cloud of comets that are so far from the Sun throughout their entire orbit that they are never visible.
It follows that the maximum diameter of the solar system can reach 1000 billion, that is, a trillion (1,000,000,000,000) kilometers or even more. It takes 40 days for a light beam to cover such a distance. Thus, we can say that the diameter of the solar system exceeds one light month.
The Earth is relatively small not only in comparison with these distances. The four outer planets - Jupiter, Saturn, Uranus and Neptune - are visible through a telescope as disks whose diameter can be measured. When the distance to these planets became known, this made it possible to calculate their true size from the apparent sizes of their disks. And each of these outer planets turned out to be a real giant compared to the Earth. And the size of the Sun makes it a giant compared to even the largest of these planets.
In addition, each of these giant planets has a satellite system that dwarfs our single-moon satellite system. The first of the satellites of the outer planets were discovered by the four largest satellites of Jupiter, which Galileo saw in 1610 with his first telescope. The last of the large satellites to be discovered was Neptune's satellite Triton, noticed in 1816 by the English astronomer William Lassell (1799-1880). Small satellites were also discovered; Neptune's second satellite, Nereid, was discovered only in 1949 by an American astronomer of Dutch origin, Gerard Peter Kuiper (born in 1905). In total, 31 satellites are now known in the solar system, together with our Moon. But it is very likely that some other small satellites will be discovered.
The following table can give an idea of the size of some satellite systems compared to the Earth satellite system.
Modern view of the size of the solar system
The modern value of the astronomical unit, expressed in kilometers:
Average distance from Earth to Sun = 149,597,870 km.
This value was obtained from several measurements, among which was a radar measurement of the distance to Mars, and the Third Law was used.
As we have already noted, if the distance between the Earth and the Sun is known, then all other distances in the Solar System become certain. The table shows data on the orbits of planets, including Pluto, which lost its status as a major planet in 2006.
Several conclusions can be drawn from the table. Venus's orbit is close to a circle, and its distance from the Sun varies by only 1%. has a very elongated orbit (not to mention Pluto!). In addition, Mars' orbit is noticeably elliptical, which made it easier for Kepler to determine its shape. The table also shows that the distance of the Earth from the Sun varies by five million kilometers. The Earth comes closest to the Sun when it is winter in the Northern Hemisphere.
To visualize the proportions of the solar system, a miniature model can be used (following the early attempts of Christiaan Huygens). Let's place in the center a sphere the size of a large apple, for example with a diameter of 10 cm. This is the Sun. And the Earth is a grain of 1 mm, which revolves around an “apple” at a distance of 1 m. Saturn revolves at a distance of 103 m.
The Sun Pluto distance in this model should be 425 m, although it may vary. If we add nearby stars to this model, they will appear at a distance of 3000 km. To be precise, this would be the system a Centauri with its two main members: star A (possibly similar to a large grapefruit) and star B (small apple), which orbit each other at a distance of 300 m. At this time, small star C (Proxima), about the size of a blueberry, will move very slowly at a distance of about 100 km from the first two stars.
We've come a long way: from the Sun illuminating Stonehenge on the summer solstice to the nearest stars four light years away. Now is the time to go back a little and look at the secrets of our home called Earth. Along with Isaac Newton, we can ask the question: “What makes an apple fall and the Earth go around the Sun?”
This is a system of planets, in the center of which there is a bright star, a source of energy, heat and light - the Sun.
According to one theory, the Sun was formed along with the Solar System about 4.5 billion years ago as a result of the explosion of one or more supernovae. Initially, the Solar System was a cloud of gas and dust particles, which, in motion and under the influence of their mass, formed a disk in which a new star, the Sun, and our entire Solar System arose.
At the center of the solar system is the Sun, around which nine large planets revolve in orbit. Since the Sun is displaced from the center of planetary orbits, during the cycle of revolution around the Sun the planets either approach or move away in their orbits.
There are two groups of planets:
Terrestrial planets: And . These planets are small in size with a rocky surface and are closest to the Sun.
Giant planets: And . These are large planets, consisting mainly of gas and characterized by the presence of rings consisting of icy dust and many rocky chunks.
And here does not fall into any group, because, despite its location in the solar system, it is located too far from the Sun and has a very small diameter, only 2320 km, which is half the diameter of Mercury.
Planets of the Solar System
Let's begin a fascinating acquaintance with the planets of the Solar System in order of their location from the Sun, and also consider their main satellites and some other space objects (comets, asteroids, meteorites) in the gigantic expanses of our planetary system.
Rings and moons of Jupiter: Europa, Io, Ganymede, Callisto and others...
The planet Jupiter is surrounded by a whole family of 16 satellites, and each of them has its own unique features...
Rings and moons of Saturn: Titan, Enceladus and others...
Not only the planet Saturn has characteristic rings, but also other giant planets. Around Saturn, the rings are especially clearly visible, because they consist of billions of small particles that revolve around the planet, in addition to several rings, Saturn has 18 satellites, one of which is Titan, its diameter is 5000 km, which makes it the largest satellite in the solar system...
Rings and moons of Uranus: Titania, Oberon and others...
The planet Uranus has 17 satellites and, like other giant planets, there are thin rings surrounding the planet that have practically no ability to reflect light, so they were discovered not so long ago in 1977, completely by accident...
Neptune's rings and moons: 
Triton, Nereid and others...
Initially, before the exploration of Neptune by the Voyager 2 spacecraft, two satellites of the planet were known - Triton and Nerida. An interesting fact is that the Triton satellite has a reverse direction of orbital motion; strange volcanoes were also discovered on the satellite that erupted nitrogen gas like geysers, spreading a dark-colored mass (from liquid to vapor) many kilometers into the atmosphere. During its mission, Voyager 2 discovered six more moons of the planet Neptune...