HET Position Angle Calculator

This program enables a PI to determine what slit position angles are allowed for a given DEC and track. The east and west tracks may have different position angle restrictions since the rho motor allows only a 180 degree rotation range. In addition there is an inherent rho rotation during any trajectory, particularly significant in the north. Warnings will be given for any potential conflict.

The current limits for the rho rotation are -110 and +90 relative to the parallactic angle for any track.

We define position angle as positive measured from north through east. Due to confusion between the optimized image quality of the parallactic angle, par, and position angle of 0, we limit the PA to be between 0.1 and 360.0, i.e. PA(north) = 360 and PA(west) = 270.

Enter the Dec and requested slit position angle below (results for the parallactic slit angle will also be returned).

DEC Position Angle
+/- o ' " o