The astronomical unit of length is now defined as exactly 149 597 870 700 meters. It is approximately equal to the mean Earth–Sun distance. It was formerly defined as that length for which the Gaussian gravitational constant ("k") takes the value when the units of measurement are the astronomical units of length, mass and time. The dimensions of "k"2 are those of the constant of gravitation ("G"), i.e., L3M−1T−2. The term “unit distance” is also used for the length "A" while, in general usage, it is usually referred to simply as the “astronomical unit”, symbol au.