The North America Nebula (NGC 7000 or
Caldwell 20) is an emission nebula in the constellation Cygnus,
close to Deneb (the tail of the swan and its brightest star).
The remarkable shape of the nebula resembles that of the
continent of North America, complete with a prominent Gulf of
Mexico. The North America Nebula is large, covering an area of
more than four times the size of the full moon; but its surface
brightness is low, so normally it cannot be seen with the
unaided eye. Binoculars and telescopes with large fields of view
(approximately 3°) will show it as a foggy patch of light under
sufficiently dark skies. However, using a UHC filter, which
filters out some unwanted wavelengths of light, it can be seen
by the naked eye under dark skies. Its prominent shape and
especially its reddish color (from the hydrogen Hα emission
line) show up only in photographs of the area.