The distance from the Earth to the Sun, expressed in terrestrial units of length, is approximately equal to 150,000,000 kilometers. In determining large astronomical distances, such a record is not entirely convenient because the distances between the rest of the planets and objects of the solar system would have to be expressed in multi-digit numbers.
The astronomical unit, which has developed in the course of history, is a unit of distance measurement in astronomy - the science of the Universe. It is mainly used to determine the distance between various objects in the solar system, but its value is also used in the study of extrasolar systems. In the 17th century, astronomers had the rational idea of using the distance separating the Sun and the Earth as a defining unit in astronomy. Since then, it has been accepted that 1 astronomical unit is equal to 149.6 million kilometers.
In the process of forming the concept of the heliocentric system of the world, the conditional distances in the solar system became well known with a fairly high accuracy. The central body of our system isThe Sun, and since the Earth revolves in a circular orbit around it, the relative distance between these two celestial bodies practically does not change. Thus, the astronomical unit corresponds to the radius of the Earth's orbit of rotation relative to the Sun. However, at that time there was still no reliable way to reliably measure this value relative to terrestrial scales. In the 17th century, only the distance to the Moon was known, and these data were not enough to determine the distance to the Sun, since the ratio of the masses of the Earth and the Sun was still unknown.
In 1672, the Italian astronomer Giovanni Cassini, in collaboration with the French astronomer Jean Richet, managed to measure the parallax of Mars. The orbits of the Earth and Mars were determined with great 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 Eros to the Earth, an even more accurate astronomical unit of measurement was determined.
In the last century, clarifications were made using radar. In 1961, the location of Venus established a new value for 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 many years of measurements, scientists found thatThe astronomical unit is increasing at a rate of up to 15 centimeters per year. This discovery significantly increases the accuracy of modern measurements of astronomical distances. One of the reasons for this phenomenon may be the loss of solar mass as a result of the solar wind.
Today it is known that the distance from the Sun to the most distant planet of our solar system - Neptune - is 30 astronomical units, and the distance from the Sun to Mars corresponds to 1.5 astronomical units.
