Position AngleThe TUB can be rotated to position Kast's slit at any desired angle. A nixie tube display in the 3-m telescope control room is the most accurate display of the TUB rotation. However, the nixie tubes display a voltage reading of the encoder pot, rather than the position angle in degrees East of North. Two programs exist to assist observers in both calculating the mean angle of atmospheric dispersion and converting position angle into nixie values. PA | NixiPA
PA is a program that calculates the mean atmospheric dispersion for a given exposure time and position of the telescope. PA is started from the user account on gouda, karnak, or shard computers by typing pa at an xterm prompt.
You will then be prompted for the following information:
Enter starting HA (hh.hh, hh:mm, or hh mm):
Enter starting Dec (dd.dd, dd:mm, or dd mm):
Length of Exposure (sec):
The average position angle and nixie readout will be displayed. This information can then be given to the Telescope Operator so that he/she can rotate the TUB to the proper position.
Enter starting HA (hh.hh, hh:mm, or hh mm): 2:34 Enter starting Dec (dd.dd, dd:mm, or dd mm): 15:37 Length of Exposure (sec): 1200 Starting HA = 2.57 Dec = 15.62 Time = 1200 seconds PA (average) = 231 (or 51) Airmass (average) = 1.35 Nixie readout = 201.0 (or 44.4)
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