Astronomical unit of measurement

The distance from the Earth to the Sun, expressed in earthly units of length, is approximately 150,000,000 kilometers. In determining large astronomical distances, such a record is not entirely convenient because the distances between the remaining planets and the objects of the solar system would have to be expressed in many-valued numbers.

The astronomical unit that has developed in the course of history is Unit of distance in astronomy - the science of the universe. Basically, it is used to determine the distance between various objects of the solar system, but its value is also used in the study of extrasolar systems. In the 17th century, astronomers had a rational idea to apply the distance separating the sun and the earth, as the determining unit in astronomy. Since then, it is commonly believed that 1 astronomical unit is 149.6 million kilometers.

In the process of formation of the idea of the heliocentric system of the world, the conditional distances in the solar system became well known with rather high accuracy. The central body of our system is the Sun, and since the Earth rotates in a circular orbit around it, the relative distance between these two celestial bodies remains practically unchanged. Thus, the astronomical unit corresponds to the radius of the orbit of the Earth's rotation relative to the Sun. However, at that time there was still no reliable way to reliably measure this magnitude with respect to terrestrial scales. In the 17th century, only the distance to the Moon was known, and these data were insufficient to determine the distance to the Sun, since the ratio of the mass of the Earth and the Sun was also unknown.

In 1672, the Italian astronomer Giovanni Cassini, in collaboration with the French astronomer Jean Richet, was able to measure the parallax of Mars. The orbits of the Earth and Mars were determined with high accuracy, and this allowed scientists to determine the distance from the Earth to the Sun. According to their calculations, the astronomical unit corresponded to 146 million kilometers. In further studies, more accurate measurements were made by measuring the orbit of Venus. And in 1901, after the approach of the asteroid of Eros to the Earth, an even more precise astronomical unit of measurement was determined.

In the last century, refinements were made using radar. In 1961, the location of Venus was established a new value of the astronomical unit, with an error of 2000 kilometers. After the repeated radar of Venus, this inaccuracy was reduced to 1000 kilometers. As a result of long-term measurements, scientists have discovered that the astronomical unit increases at a rate of up to 15 centimeters per year. This discovery greatly increases the accuracy of modern measurements of astronomical distances. One of the reasons for this phenomenon may be the loss of the solar mass as a result of the solar wind.

Today it is known that the distance from the Sun to the outermost planet of our Solar system - Neptune - is 30 astronomical units, and the distance from the Sun to Mars corresponds to 1.5 units of astronomical measurement.