Astronomy Science ~ What is the distance Earth - Sun? The easiest answer is 1 Astronomical Unit (au) . It was an easy way to remember the d...

**Astronomy Science**~ What is the distance Earth - Sun? The easiest answer is

**1 Astronomical Unit (au)**. It was an easy way to remember the distance Earth - Sun or as a distance scale in the Solar System. Is much easier to remember a distance of Mars - Sun approximately 1.5 au than the actual distance that hundreds of millions km.

Well number 1 au is also not appear suddenly but from long calculations started by

*Aristarchus of Samos*, Greece Classical century thinkers. He estimated the distance Earth-Sun only 20 times the

*Earth-Moon distance (384 000 km)*, but it missed estimates far as Earth-Sun distance turns out about 390 times the Earth-Moon distance.

Precision measurement was first performed in 1672 by

**Giovanni Cassini**and his colleague Jean Richer observing Mars from two different locations in Paris and French Guiana. By using a parallax system, astronomers have managed to calculate the distance of the Earth - Mars and use the results to calculate the distance Earth - Sun. The result they found that the distance between the Earth - Sun 140 million km. Not too far from the calculation to date.

This parallax calculation system is the only reliable method of calculation to calculate distances in the Solar System. And the average distance of the Earth - Sun, 149 597 870 691 meters, then defined as 1 Astronomical Unit are also used to express the distance in the scale of our solar system.

But amendments to the IAU 1976 System of Astronomical Constants define the astronomical unit as the "radius of a circular orbit around the sun that moves with the motion of the average 0.01720209895 radians per day". This is done with the assumption that the distance Earth - Sun can not be calculated accurately. Price

**0.01720209895 is a constant Gauss**.

Determination of the definition of 1 au is based on Gaussian constant is difficult for astronomers working in the modeling of the Solar System. How come? When Einstein introduced his theory of general relativity, then we know that space-time is relative depending on the location of the observer. Thus the astronomical unit is also shifted to a thousand meters even when the terms of reference shift. Although the spacecraft was to shift the case has no effect because the distance has been calculated by the reference frame of the Earth.

Another problem comes from the sun. Gauss constant dependent on the mass of the Sun (k = (GMs) 1/2). So when the Sun is in the mass loss when it radiates energy, constant Gauss was changed and that means another astronomical unit is also changing slowly.

But the development of today's technology has been able to measure the distance of the Earth - Sun with a high degree of accuracy. The distance measurement can be performed using a laser or a subordinate space. Therefore it is necessary to redefine the appropriate price 1 au for general use.

In the IAU GA in Beijing, China redefinition is done through voting IAU members were present. The results are approved by the designation

**149 597 870 700 meters as 1 au**, and the symbol "au" is used to express the Astronomical Unit or Astronomical Units.

So if the re-definition of this effect on Earth? Of course not. Earth remain in place and will continue to move around the barycenter which is very close to the sun. But for astronomers au pricing 1 indicates that this time mankind has been able to determine the precise distance between the Earth - Sun.