The house we live in is our solar system. It is still unknown whether we are alone in the universe. Celestial bodies are scattered throughout the Cosmos, and life may well exist in its other manifestations not only on Earth. Solar heat gives birth to life on our planet, because the Sun is our only star.
The celestial bodies of our system
The sun is the center of our system. The motion of celestial bodies is carried out around the sun in separate orbits. Thermonuclear reactions do not occur on planets. The sun, thanks to reactions, heats the planets that revolve around it. All planets are large and have a spherical shape, which they acquired as a result of evolution.
Astrologers used to assume that there are only seven planets in the solar system. These are the Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn.
A very long time ago, before the opening of the Solar System, people believed that the Earth is the center of everything and all cosmic celestial bodies, including the Sun, move around it. Such a system was called geocentric.
In the XVI century, Nicholas Copernicus proposed a new system for constructing the World, called heliocentric. Copernicus stated that in the center of the world is the sun, not the earth. The change of day and night occurs due to the rotation of our planet around its own axis.
Other solar systems
The invention of the telescope allowed people to see for the first time that comets are moving in the sky, which come closer to the Earth, and then leave it. After almost 20 centuries, scientists have determined that cosmic celestial bodies are able to rotate not only in orbit around the Earth or the Sun. This conclusion came when they discovered the existence of the moons of Jupiter.
Are there other planet systems for other stars? Absolutely precisely, this is not yet known, but there is no doubt in their existence.
In 1781, the discovery of the large and far-off planet Uranus followed, i.e. there were not seven planets, and the space hierarchy system was revised.
For a long time there was an opinion that the decay or formation of a planet between Mars and Jupiter gave rise to all asteroids. To date, scientists have more than 15,000 asteroids.
In recent years, they have discovered celestial bodies, which are difficult to attribute to any particular class, comets or planets. The orbits of these objects are very elongated, but there are no signs of tail and comet activity.
Two kinds of planets
The planets of our system are classified into giants and terrestrial groups. The difference between the planets of the earth group is a large average density and a solid surface. Mercury, in comparison with other planets, has a higher density due to an iron core, which makes up 60% of the mass of the entire planet. Similar to Earth in mass and density Venus.
The Earth differs from other planets in the rather complex structure of the mantle, the depth of which is 2900 km. Underneath is a core, presumably a metal one. Mars has a relatively low density, and its mass is no more than 20%.
Celestial bodies belonging to the group of giant planets have a low density and a complex atmospheric chemical composition. These planets are composed of gas and their chemical composition is close to that of the sun (hydrogen and helium).
Scientists agreed to consider the planet as celestial bodies orbiting a Sun-star, possessing strong gravitational attraction, spherical shape and occupying a separate orbit.