From rgm@ast.cam.ac.uk Wed Dec 25 16:56:51 2002 Date: Sun, 16 Jun 2002 16:50:18 +0100 (BST) From: richard mcmahon at IOA To: Weimin Yuan Cc: Mike Watson , Jonathan Tedds Subject: Re: observing in Moon nights I would stay at least 30degrees; ie. around 2hrs in RA away from the moon. By now it is probably to bright to observe in g when the moon is up. You need to increase the exposure times when the sky is bright as follows: * Exposure times in moonlight * Formally the exposure time needs to be increased linearly with sky brightness if you want to attain a uniform limiting magnitude. * Take action if the sky goes more 25% above the values above by making exposure time 50% longer. [this will overcompensate but it avoids human errors which occur when observers try to micro-manage the expsoure times. * When the sky brightness reaches 50% above the above double the nominal exposure. * Donot go more than x2 on the nominal exposure times since then the survey speed drops. It is probably better do a redder band or move further from the moon. Note the sky value you measure on the screen includes bias level so you need to subtract this. r. On Sun, 16 Jun 2002, Weimin Yuan wrote: > Date: Sun, 16 Jun 2002 04:59:26 +0100 (BST) > From: Weimin Yuan > To: Richard McMahon > Cc: Mike Watson , Jonathan Tedds > Subject: observing in Moon nights > > Hi Richard, > > We are now approaching to the bright Moon nights. > Is there any minimal angle at which we should keep the > telescope away from the Moon? (Moon phase dependent?). > We'd take this into account when planning the observations. > regards > Weimin > -------------------------------------------------------------------------- Dr. Richard G. McMahon | Phone (office) 44-(0)-1223-337519 University of Cambridge | (switchboard) 1223-337548 Institute of Astronomy | (secretary) 1223-337516 Madingley Rd | FAX 1223-337523 Cambridge, CB3 OHA, UK. | mobile (0)-7885-409019 office: Hoyle 8 | home 1223-464920 --------------------------------------------------------------------------- email: rgm@ast.cam.ac.uk | WWW: http://www.ast.cam.ac.uk/~rgm ---------------------------------------------------------------------------