Pan.
In the Sin projection, this attempts to rotate the sphere,
with north staying vertical on the screen, in such a way that the
same part of the sky stays under the cursor position.
At low magnifications this is sometimes not possible;
if the mouse starts on the sphere and ends up off it the navigation
will be jerky.
The Aitoff and Plate Carée projections act like a piece of
paper that can be dragged around in two dimensions in the usual way.