On March 13, 1781, English astronomer William Herschel discovered the seventh planet 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 is 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 XX and beginning of XXI centuries, many objects have been 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 as plutoids all objects whose absolute asteroid magnitude (brilliance from a distance of one astronomical unit) brighter +1. 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
From the school astronomy course, which is included in the geography lesson program, we all know about the existence of the solar system and its 8 planets. They “circle” around the Sun, but not everyone knows that there are celestial bodies with retrograde rotation. Which planet rotates in the opposite direction? In fact, there are several of them. These are Venus, Uranus and a recently discovered planet located on the far side of Neptune.
Retrograde rotation
The movement of each planet obeys the same order, and the solar wind, meteorites and asteroids, colliding with it, force it to rotate around its axis. However, gravity plays the main role in the movement of celestial bodies. Each of them has its own inclination of the axis and orbit, the change of which affects its rotation. Planets move counterclockwise with an orbital inclination angle of -90° to 90°, and celestial bodies with an angle of 90° to 180° are classified as bodies with retrograde rotation.
Axis tilt
As for the axis tilt, retrograde given value is 90°-270°. For example, the axis tilt angle of Venus is 177.36°, which does not allow it to move counterclockwise, and the recently discovered space object Nika has an inclination angle of 110°. It should be noted that the effect of the mass of a celestial body on its rotation has not been fully studied.
Fixed Mercury
Along with retrograde ones, there is a planet in the solar system that practically does not rotate - this is Mercury, which has no satellites. Reverse rotation of planets is not such a rare phenomenon, but it is most often found outside the solar system. Today there is no generally accepted model of retrograde rotation, which makes it possible for young astronomers to make amazing discoveries.
Causes of retrograde rotation
There are several reasons why planets change their course of motion:
- collision with larger space objects
- change in orbital inclination angle
- change in axis tilt
- changes in the gravitational field (interference of asteroids, meteorites, space debris, etc.)
Also, the cause of retrograde rotation may be the orbit of another cosmic body. There is an opinion that the reason reverse movement Venus could have been hit by solar tides that slowed down its rotation.
Formation of planets
Almost every planet during its formation was subjected to many asteroid impacts, as a result of which its shape and orbital radius changed. An important role is also played by the fact that a group of planets and a large accumulation of space debris are formed nearby, resulting in a minimum distance between them, which, in turn, leads to a disruption of the gravitational field.
Our home in space is the Solar System - a star system consisting of eight planets and part of the galaxy Milky Way. In the center is a star called the Sun. The solar system is four and a half billion years old. We live on the third planet from the sun. Do you know about other planets in the solar system?! Now we will tell you a little about them.
Mercury- the smallest planet in the solar system. Its radius is 2440 km. The period of revolution around the Sun is 88 Earth days. During this time, Mercury manages to rotate around its own axis only one and a half times. A day on Mercury lasts approximately 59 Earth days. The orbit of Mercury is one of the most unstable: not only the speed of movement and its distance from the Sun, but also the position itself changes there. There are no satellites.
Neptune- the eighth planet of the solar system. It is located quite close to Uranus. The radius of the planet is 24547 km. A year on Neptune is 60,190 days, that is, about 164 Earth years. Has 14 satellites. It has an atmosphere in which the strongest winds have been recorded - up to 260 m/s.
By the way, Neptune was discovered not through observations, but through mathematical calculations.
Uranus- the seventh planet in the solar system. Radius - 25267 km. The coldest planet has a surface temperature of -224 degrees. A year on Uranus is equal to 30,685 Earth days, that is, approximately 84 years. Day - 17 hours. Has 27 satellites.
Saturn- the sixth planet of the solar system. The radius of the planet is 57350 km. It is second in size after Jupiter. A year on Saturn is 10,759 days, which is almost 30 Earth years. A day on Saturn is almost equal to a day on Jupiter - 10.5 Earth hours. It is most similar to the Sun in the composition of chemical elements.
Has 62 satellites.
The main feature of Saturn is its rings. Their origin has not yet been established.
Jupiter- the fifth planet from the Sun. It is the largest planet in the solar system. The radius of Jupiter is 69912 km. This is already 19 times more than Earth. A year there lasts as many as 4333 Earth days, that is, almost less than 12 years. A day is about 10 Earth hours long.
Jupiter has as many as 67 satellites. The largest of them are Callisto, Ganymede, Io and Europa. Moreover, Ganymede is 8% larger than Mercury, the smallest planet in our system, and has an atmosphere.
Mars- the fourth planet of the solar system. Its radius is 3390 km, which is almost half the size of the Earth. A year on Mars is 687 Earth days. It has 2 satellites - Phobos and Deimos.
The planet's atmosphere is thin. Water found on some areas of the surface suggests that some kind of primitive life on Mars was once before or even exists now.
Venus- the second planet of the solar system. It is similar in mass and radius to the Earth. There are no satellites.
The atmosphere of Venus consists almost entirely of carbon dioxide. The percentage of carbon dioxide in the atmosphere is 96%, nitrogen - approximately 4%. Water vapor and oxygen are also present, but in very small quantities. Due to the fact that such an atmosphere creates a greenhouse effect, the temperature on the surface of the planet reaches 475 °C. A day on Venus is 243 earthly days. A year on Venus is 255 days.
Pluto is a dwarf planet at the edges of the solar system, which is the dominant object in a distant system of 6 small ones cosmic bodies. The radius of the planet is 1195 km. Pluto's orbital period around the Sun is approximately 248 Earth years. A day on Pluto is 152 hours long. The mass of the planet is approximately 0.0025 the mass of the Earth.
It is noteworthy that Pluto was excluded from the category of planets in 2006 due to the fact that in the Kuiper belt there are objects that are larger or equal in size to Pluto, which is why, even if it is accepted as a full-fledged planet, then in this case it is necessary add Eris to this category - which has almost same size with Pluto.
Quick answer: 8 planets.
The solar system is a planetary system that includes the central star, which is the Sun, as well as all other natural space objects, which in turn revolve around the Sun.
Interestingly, most of the total mass of the solar system is accounted for by itself, while the rest is accounted for by 8 planets. Yes, yes, there are 8 planets in the solar system, and not 9, as some people believe. Why do they think so? One reason is that they mistake the Sun for another planet, but in fact it is the only star included in the solar system. But in reality everything is simpler - Pluto was previously considered a planet, but is now considered a dwarf planet.
Let's begin the review of the planets, starting with the one closest to the Sun.
Mercury
This planet was named after the ancient Roman god of trade - the fleet-footed Mercury. The fact is that it moves much faster than other planets.
Mercury completely revolves around the Sun in 88 Earth days, while the duration of one sidereal day on Mercury is 58.65 Earth days.
Relatively little is known about the planet, and one of the reasons is that Mercury is too close to the Sun.
Venus
Venus is the second so-called inner planet of the solar system, which was named after the goddess of love, Venus. It is worth noting that this is the only planet that received its name in honor of a female deity, rather than a male one.
Venus is very similar to Earth, not only in size, but also in composition and even gravity.
It is believed that Venus once had many oceans, similar topics what we have. However, some time ago the planet heated up so much that all the water evaporated, leaving behind only rocks. Water vapor was carried into outer space.
Earth
The third planet is Earth. It is the largest planet among the terrestrial planets.
It was formed approximately 4.5 billion years ago, after which it was almost immediately joined by its only satellite, which is the Moon. It is believed that life on Earth appeared about 3.9 billion years ago and over time its biosphere began to change into better side, which made it possible to form ozone layer, increase the growth of aerobic organisms, etc. All this, among other things, allows us to exist now.
Mars
Mars closes the four terrestrial planets. The planet is named after the ancient Roman god of war, Mars. This planet is also called red because its surface has a reddish tint due to iron oxide.
Mars has surface pressure 160 times less than Earth's. On the surface there are craters similar to those that can be seen on the Moon. There are also volcanoes, deserts, valleys and even ice caps.
Mars has two satellites: Deimos and Phobos.
Jupiter
It is the fifth planet from the Sun and the first among the giant planets. By the way, it is the largest in the solar system, which received its name in honor of the ancient Roman supreme god of thunder.
Jupiter has been known for a long time, which is reflected in ancient myths and legends. Has very a large number of satellites - 67 to be exact. Interestingly, some of them were discovered several centuries ago. Thus, Galileo Galilei himself discovered 4 satellites in 1610.
Sometimes Jupiter can be seen with the naked eye, as was the case in 2010.
Saturn
Saturn is the second largest planet in the solar system. It was named after the Roman god of agriculture.
It is known that Saturn consists of hydrogen with signs of water, helium, ammonia, methane and others heavy elements. An unusual wind speed was observed on the planet - about 1800 kilometers per hour.
Saturn has prominent rings that are mostly made of ice, dust, and other elements. Saturn also has 63 satellites, one of which, Titan, is larger than even Mercury.
Uranus
The seventh planet in terms of distance from the Sun. It was discovered relatively recently (in 1781) by William Herschel and was named after the god of the sky.
Uranus is the first planet to be discovered using a telescope, between the Middle Ages and modern times. Interestingly, although the planet can sometimes be seen with the naked eye, before its discovery it was generally believed that it was a dim star.
Uranus has a lot of ice but no metallic hydrogen. The planet's atmosphere is composed of helium and hydrogen, as well as methane.
At Uranus a complex system rings, there are also 27 satellites at once.
Neptune
Finally, we have reached the eighth and last planet of the solar system. The planet is named after the Roman god of the seas.
Neptune was discovered in 1846, and, interestingly, not through observations, but thanks to mathematical calculations. Initially, only one of its satellites was discovered, although the remaining 13 were not known until the 20th century.
Neptune's atmosphere consists of hydrogen, helium and possibly nitrogen. The strongest winds rage here, the speed of which reaches a fantastic 2100 km/h. IN upper layers The atmosphere temperature is about 220°C.
Neptune has a poorly developed ring system.