See http://www.cleardarksky.com/c/ApachePtNMkey.html We know very little about this beyond what is explained at the above web site, but it would obviously be very useful if it turns out to be sufficiently accurate/reliable. I call it to the attention of anyone who might be interested in comparing their predictions to the reality they encounter while observing at APO. Ed Turner APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 617 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-general/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO