Globe at Night 2010
computed for the so-called zenith extinction of 0.25 mag using
a programme map_bsct (accessible even online through map.php
for a contemporary directory 2009-2012-2014...
Equidistant projection onto a cone (below latitude 50 N) or
a cylinder (50 and 60 N).
For cylinders, undistorted parallel is at the Belt of Orion,
for cones, there are two such parallels at 8 degrees from the Belt.
The Bright Star Catalogue has been
used for the maps 0 mag to 5 mag (Betelgeuse shown at its maximum light),
the original Hipparcos for 6 mag and 7 mag (Delta Orionis is too faint
in the Czech version, due to a bug in the map_bsct programme; the bug
has been corrected in October 2010 and another map sets renewed).
The limits are for the amounts of light entering the eyes of observers,
i.e., starlight is attenuated by the atmosphere.