PA and sep

While viewing λ (lambda) Orion last week, and checking Haas's notes, I realised it was high time that I learn Position Angle and begin to incorporate it into my notes of double stars.

Tonight, I did a little sketch to help me get more clear about it.



The primary star is in the centre (yellow); the secondary is below and to the right (blue). Position Angle (PA) is measured from north (so you need to know where the North Celestial Pole is) and goes counter-clockwise around the primary.

So, roughly, accordingly to this diagram, the PA for the blue companion is 225 degrees.