LWS
Position Angles

Quick Reference Tables

LWS Orientations: PA(LWS) =ROTPOSN - 64° or =SKYPA+206°
Desired LWS Orientation SKYPA ROTPOSN
North UP 154° 64°
North RIGHT 244° 154°
North DOWN 334° 244°
North LEFT 64° 334°

TV Guider Orientations: PA(TV)=SKYPA+90°
Desired TV Orientation SKYPA ROTPOSN
North UP 270° 180°
North RIGHT 180° 90°
North DOWN 90°
North LEFT 270°

Notes:


LWS Position Angle FAQs

What is the meaning of the SKYPA value displayed on FACSUM?
The SKYPA value displayed in FACSUM represents the position angle of the guider FOV relative to the center of the LWS FOV in the focal plane.
What is the position angle of an image displayed on the LWS detector?
The position angle of both the LWS slit and LWS detector columns with respect to celestial North is given by SKYPA+206°.
What is the position angle of the LWS slit?
See previous answer; the LWS slit is aligned with the detector columns. Also see next question.
Can I use any position angle with LWS?
Usually the choice of position angle is constrained by the need to place a guide star on the TV guider. Since the guider and LWS rotate together in the Forward Cassegrain Module, the LWS position angle cannot be set independently of the guider.
What is the position angle of the TV guider display?
The position angle of guider columns with respect to celestial North is given by SKYPA+90°.
How do I orient LWS so that North is "up" on my images?
Set SKYPA to 154°.
How do I orient the guider so that North is "up" on my guider display?
Set SKYPA to 270°.
My image header only lists the ROTPOSN keyword. How can I tell to which position angle this corresponds on my LWS image?
Given ROTPOSN, the following relationship gives the LWS position angle: PA(LWS) = ROTPOSN + 296°.

LWS Position Angle Diagram

The following diagram demonstrates the relationships between the various LWS position angles for an arbitrary SKYPA value.

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Last modified: Tue Dec 21 22:13:34 HST 1999