RE: (IAAC) Obj: NGC 604 - Inst: 200mm Newtonian
Aren't there actually mapped features of the Milky Way which are
essentially this large, Paul - but are too diffuse to be readily
observed visually? I'd always understood the huge nebulous area
around the Gum Nebula to represent a single identifiable entity.
And long-exposure, wide-angle images of Orion make most of that
constellation's area of the sky appear to be one vast nebula...
You are correct, the Gum Nebula is not only huge, 1000 LY diameter (about 40
degrees across the sky), but also very close. It's front edge is 450 LY away,
while the back edge is 1500 LY away. The big difference between the Gum and NGC
604 nebulae is that the Gum is probably a very old supernova remnant
(expanding), while NGC 604 is a stellar nursery in a contracting gas cloud, the
same as M 42 or M 8. Hundreds of young bright stars in NGC 604 illuminate the
cloud to a much higher surface brightness than the Gum. If NGC 604 were to be
moved to our neighborhood in our galaxy it would be quite spectacular.
As far as the Orion Nebula, it covers almost 10 degrees of sky, if only you
could see it's faint outer reaches. See http://vis.sdsc.edu/research/orion.html
for a very cool visualization of this remarkable object.
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