The figure shows a cube of edge $1$ unit with a corner $O$ at the origin. The red line is the body diagonal $OG$ and the blue edge $OA$ lies along the $x$-axis. What is the angle between $OG$ and $OA$?

Fig. 1: A cube of edge 1 with one corner O at the origin and three edges along the x, y and z axes. The opposite corner is labelled G. A red line joins O to G, the body diagonal, and the edge OA along the x-axis is drawn in blue. The other edges are thin grey lines.