To measure the approximate angular separation between two objects simply position the cursor over the first of them, and then click and hold down mouse button three. Continuing to hold down this mouse button, move the cursor until it is positioned over the second object.
A `rubber band' cursor is drawn as the mouse moves. It shows the vector between the original and current positions and also the offsets in two orthogonal coordinates. The separation and offsets are all labelled with their size in minutes of arc, with a sexagesimal subdivision into seconds.
The cursor disappears when the mouse button is released.
The GAIA Cookbook