Astronomers have redefined one of the most commonly used stellar distances, the astronomical unit (AU). Based on the rough distance from Sol to Earth, AU has been transformed from a confusing equation to a simple number.
Astronomers had adopted this simplification at this past summer’s International Astronomical Union meeting in Beijing, China, making the astronomical unit (AU) 149,597,870,700 meters.
Previously, the AU was known as the radius of an unperturbed circular Newtonian orbit about the Sun of a particle having infinitesimal mass, moving with a mean motion of 0.01720209895 radians per day (known as the Gaussian constant).
While it baffled astronomy students, it also clashed with Einstein’s general theory of relativity, which tended to shift the AU’s distance by about a thousand kilometers, depending on where the observer is located. Traditionally, the AU is linked to the mass of Sol, but since Sol is continually losing mass, the AU has been slowly changing as well.
With the AU being a single number, it simplifies all of these problems and stays away from issues linked to the location of the observer. It is now a fixed number of kilometers, which is far easier to understand.