distance from the Earth to the Sun, to put terrestrial units of length, approximately 150 million kilometers.In the definition of large astronomical distances such record is not very convenient because of the distance between the other planets and the objects of the solar system would have to express many-valued numbers.
developed during the history of the astronomical unit, it is unit of distance in astronomy - the science of the universe.It is mainly used to determine distances between the different objects of the solar system, but its value is also used in the study of extrasolar systems.In the 17th century, astronomers appeared rational to apply the idea of distance between the Sun and the Earth, as the determining unit in astronomy.Since it is assumed that 1 astronomical unit is equal to 149.6 million kilometers.
In the process of the formation of ideas about the heliocentric system of the world conditional distances in the solar system became well known with sufficient accuracy.The central body of our system is the sun, and as the Earth rotates in a circular orbit around it, the relative distance between the two celestial bodies does not change.Thus, the astronomical unit corresponds to the radius of Earth's orbit relative to the sun.However, in those days it did not exist a reliable way to reliably measure the relative value of earthly proportions.In the 17th century it was known only to the distance to the Moon, and these data were insufficient to determine the distance to the sun, because the ratio of the mass of the Earth and the sun, too, was still unknown.
In 1672, Italian astronomer Giovanni Cassini in collaboration with the French astronomer Jean Richer was able to measure the parallax of Mars.The orbits of Earth and Mars have been identified with high accuracy, and this allowed the scientists to determine the distance from the Earth to the sun.According to their calculations, the astronomical unit corresponds to 146 million kilometers.Further studies were carried out more precise measurements by measuring the orbit of Venus.And in 1901, after the asteroid Eros rendezvous with Earth, it was determined more accurate astronomical unit of measure.
In the last century refinement produced with the help of radar.In 1961, the location of Venus was set the new value of the astronomical unit with an accuracy of 2,000 kilometers.After the re-radar Venus this uncertainty has been reduced to 1,000 kilometers.As a result, long-term measurements, the scientists discovered that the astronomical unit is increased up to 15 centimeters per year.This discovery greatly increases the accuracy of the current measurements of astronomical distances.One reason for this phenomenon may be a loss of solar mass by the solar wind.
Today we know that the distance from the Sun to the most distant planets in our Solar System - Neptune - is 30 astronomical units, and the distance from the Sun to Mars corresponds to 1.5 astronomical units of measurement.
