But galaxies are not created only by stars, the space among stars
is not empty, despite the matter here so thin that nobody would
hesitate to call it perfect vacuum (we intentionally omit
dark matter here). And still, despite the hydrogen atoms are so
sparse, long exposure astrophotography shows their collective glow as
a red background where we would expect black emptiness, like on the
wide-field image of a part of constellation Cygnus by Paolo Moroni
(notice the Crescent nebula in the left part of the
image).
Paolo used his G2-8300 camera with Samyang 135 mm F/2 lens and Sky-Watcher ED80 telescope with
0.85× Focal Reducer. Total exposure time
reached 30 hours.
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