Right ascension and declination identify an object's position in the sky, but if we are looking at something through a telescope, there is a third angle of interest, namely how our view is rotated relative to the point we are looking at.
We could could think of this angle as a sort of celestial roll that goes with RA (yaw), and D (pitch).
Is there a standard name for this "roll" angle as a third element with RA and D?
What is its reference direction? (Orthogonal to the direction given by RA and D, in the plane containing that direction and the north pole?)
And would increasing the angle turn our view clockwise, or counterclockwise?