An astronomical unit (abbreviated au) was a unit of measure on the interplanetary scale, roughly equal to the (average) distance between Earth and Sol. One astronomical unit was equal to 150 million kilometers, or approximately 93 million miles.
The map of the inner system of the Talosian system depicted the distance from the binary stars on a line. At every ten intervals, there was a mark which represented one astronomical unit. The map showed that the inner system reached 3.4 astronomical units. (TOS: "The Cage")
In the original version of the film, V'ger's cloud was actually 82 au across. At their farthest point from each other (the aphelion), Earth and Pluto are just over 49 au apart. This would have made V'Ger's cloud almost twice that length, engulfing over half the solar system. As a result, the cloud size was toned down to a more reasonable number in the 2001 director's edition but even then, 2 au, the diameter of the Earth's orbit, is still an enormous size.