At the meeting in Beijing, the International Astronomical Union conference, present her scientists decided that would make a redefinition of the astronomical unit. One astronomical unit will continue to be equal to the distance from the Earth to the Sun, but at the same time, scientists now will be secure the monotonous exact evaluation. Now assumed the value of one astronomical unit is equal to 149597870700 meters.
For ordinary people in the world, this innovation has absolutely no practical use, the input of such a fixed constant in the first place, of course, is for astronomers and is designed to facilitate their work and get rid of unnecessary calculations.
Back in 1672, Giovanni Cassini observed the Mars the while in Paris, at the same moment, the other equally well-known astronomer, Jean Richer, watching Mars from French Guiana. Similarly, astronomers, taking into account parallax, were able to calculate the distance to Mars, and then, in the same way and calculated the distance to the sun, which was taken as one astronomical unit. Since then, the value of the astronomical unit is not counted again, but always, the resulting value is the result of translation with the use of a different combination of universal constants that may change and interchangeable, which would lead to a difference in the outcome.
Among other things, contribute to this question makes, of course, and the general theory of relativity, which takes into account the position of the observer. For example the same distance from Earth to the Sun, but observed from Jupiter, will be different from the "ground" option at least several thousand meters. Although spacecraft that in outer space moving in a straight line like that does not matter, but it is also extremely difficult to work paleontologists who work on models of the solar system.
Redefine the astronomical unit, giving it a clear meaning; it was possible for at least several decades. However, do not accept it "conservatives" who are present in the astronomical community. It is likely that at a conference in Beijing, the reformers were never as convincing and conservatives surrendered their positions, by agreeing to what would the astronomical unit was taken as a certain number.