Date: Thu, 25 Jun 1998 05:30:28 -0600
From: long@apo.nmsu.edu (Dan Long)
Subject: 2.5m night report 980624
                         WEDNESDAY JUNE 24, 1998
                     APACHE POINT OBSERVATORY SDSS 2.5m
                              OBSERVING  LOG
     The enclosure was opened at about 19:00.  The doors were opened,
  but the building was not rolled off.  The fans were turned on.  Also,
  the gap between the telescope and the windscreen platform was covered
  with tape to improve airflow around the primary.  All of this  was an
  attempt to equalize the telescope to ambient temperature but keep
  sunlight off the telescope.
     We were able to start taking data shortly before astronomical
  twilight ( 22:00 ).  Partly cloudy skies prevented us from being able
  to start sooner.  The ventilation seemed to help as images looked
  good from the start rather than taking a couple hours to settle down.
     The telescope was moved into a position two hours west of the
  meridian on the equator.  Thanks goes to the Fermi crew for their
  work in getting the windscreen to track the telescope in azimuth at
  higher speeds.  It made setting up much quicker.
     The weather tonight started out partly cloudy, but by the time
  astronomical twilight rolled around it was mostly clear.  About half
  an hour later it became clear and stayed that way the rest of the
  night.  Like last night the temperatures stayed in the mid 60s almost
  the entire night.  This made for some of the best seeing we've yet
  had from the 2.5m.  Most images were in the 1.1 to 1.4 arcsecond fwhm
  range, and at one point reaching 0.95" in r!
     We got nearly two hours of data at fairly high galactic latitude
  between about 10 PM and midnight ( 15 and 17 hours ).  A problem with
  the pool not getting trimmed caused a break in the data around midnight.
  Scanning resumed and continued for another 4 hours going over the same
  area covered by the dark run in May.
     The last part of the night was spent working on the focus loop
  software.  Astroline is now correctly determining the needed
  secondary moves.
     One odd thing I noticed.  The telescope was parked in the same
  position all night and both the altitude and azimuth brakes were on.
  Both the azimuth and rotator positions stayed the same within a few
  arcseconds as one would expect.  however, the altitude reading changed
  by over three arcminutes ( 12,000 counts ) during the night despite
  the brake being on the whole time.  I suspect that the encoders are
  drifting rather than the telescope actually moving, but such a large
  drift is a bit alarming.  If we park again for such a long period,
  I'll note the altitude inclinometer position and see if it changes any.
     The telescope was closed up for the night at 05:00.
                                   Dan