Changes between Version 31 and Version 32 of PublicPages/MayallZbandLegacy/NotesforObservers/Problems

Timestamp:

Feb 6, 2016 12:01:35 AM (9 years ago)

Author:

David Schlegel

Comment:

--

PublicPages/MayallZbandLegacy/NotesforObservers/Problems

@@ -154 +154 @@
 If observing near zenith, the lower part of the dome slit can also be closed.  That lower part of the slit only starts
 vignetting the telescope if observing to airmasses larger than 2.
+
+=== 8. Bad telescope pointing ===
+
+'''Symptoms:''' The reported telescope offsets from the python "obsbot" or the IDL "mosstat" show
+that the pointing has gone off by more than 20 arcsec.  The "mosstat" script will likely fail to match
+stars if this offset is larger than 20 arcsec.
+
+'''Frequency:''' This happened many times per night in 2015, but should happen only rarely now.
+
+'''Fix:'''
+The operator will need to recenter the telescope. One can do this by
+telling the OA to offset the telescope in the *OPPOSITE* direction of the computed mosstat positional offsets, i.e., if you see: 
+{{{
+   RA, Dec offsets: -15.230 14.756
+}}}
+ask the OA to offset the telescope +15" in RA (i.e., east) and -15" in DEC (i.e., south) and zero the coordinates there. Only 
+apply these offsets when the exposure is done (i.e., during readout) and when the telescope is not moving!
+
+One can also check the observing progress using the almanac command:
+{{{
+  IDL> almanac, 10001, /noprint
+}}}
+will print out a summary of all the frames from 10001 to the present in a nice tabular form (widen the window).  This is useful for checking how the seeing and sky brightness have varied since frame 10001, and whether  one should create and upload a new JSON observing script. The /noprint just prevents the decstat output for every frame; if you want to see that, then don't use the /noprint keyword. 
+
+