Starting off with a single 5-minute exposure taken on 16th December 2004 at a reasonably dark location at the Ghubra Bowl in Oman, elevation around 680m and ending with a stack of 20. Conditions were dark enough that you could unambiguously locate M31 with the naked eye. While the sky was not very dark all over (some scattered wispy clouds and a bit of haze in various directions, and a crescent Moon to boot!) it did look pretty dark in the direction of M31, eg spiral arms were easily visible in M33 through a 20" Obsession. Very often it is the transparency of the sky that determines how bad is the sky fog in a particular direction that you are photographing with a long lens or telescope. Hence altitude above sea level always helps, also a bit of rain the previous day. Of course, to shoot ultrawide angle Milky Way pictures you need the sky to be dark all over... For other stuff peruse my primary website: http://www.samirkharusi.net/