Galaxy, also known as the Milky Way,It consists of a large number of stars - about 200 billion, but the exact number is impossible to calculate. Many of them form a planetary system like our solar.
So far, scientists have found about a thousand of these systems, but there is still a lot of discoveries.
Milky Way - the galaxy in which theThe solar system and the planet Earth. It has the shape of a spiral with a jumper from the center depart several branches, and all the stars are in the galaxy, orbiting its nucleus. Our sun is almost at the edge and makes a complete revolution in 200 million years. It forms the most famous humanity planetary system called Solar. It consists of eight planets and a variety of other space objects formed from gas and dust cloud about four and a half billion years ago. The solar system is relatively well understood, but the stars and other objects beyond are at great distances, despite belonging to the same galaxy.
All the stars that people can watchthe naked eye from Earth, located in the Milky Way. Do not confuse the galaxy under this name to the phenomenon that occurs in the night sky: a bright white stripe that crosses the sky. It is - part of our galaxy, a large cluster of stars that looks like this due to the fact that the Earth is located next to the plane of symmetry.
Planetary systems in the Galaxy
Only one planetary system is calledSolar - one in which the Earth is. But in our galaxy there are many systems that are open only a small part. Until 1980, the existence of such systems had only our hypothetical: surveillance methods did not allow to detect such a relatively small and dim objects. The first assumption of their existence did the astronomer Jacob of the Madras Observatory in 1855. Finally, the first planet outside the solar system was discovered in 1988 - it belonged to the orange giant Gamma Cephei A. This was followed by other discoveries, it became clear that they can be set. Such planets, do not belong to our system, called exoplanets.
Today, astronomers know more than a thousandplanetary systems, about half of them have more than one exoplanets. But there are still many candidates for the title, while the methods of investigation could not confirm these data. Scientists suggest that in our galaxy there are about a hundred billion exoplanets, which belong to several tens of billions of systems. Probably about 35% of all Sun-like stars of the Milky Way are not alone.
Some planetary systems found quitenot like the sunshine, others have more similarities. In some there are only gas giants (as long as the information about them, because they are easier to detect), in others - a planet similar to Earth.