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#1
September 19th 03, 09:52 AM
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Names of Galaxies?
Why are some galaxies called M(some number) and NGC(some number)? What's the
difference and what does each initial or letter represent? Thank you. 
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#2
September 20th 03, 11:26 AM
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Zarkovic wrote:
Why are some galaxies called M(some number) and NGC(some number)? What's the difference and what does each initial or letter represent? Thank you. Just to add a couple of points to what Rick said: Both the Messier and NGC catalogues include many objects within our own galaxy -- planetary nebulae, diffuse nebulae, galactic clusters, and globular clusters -- as well as external galaxies. Messier's initial motivation for compiling his catalogue was to list the permanent "fuzzies" that might be mistaken for passing comets. The M objects are in no particular sequence except that in which Messier happened to observe them (the last few were added by later observers), but the NGC numbers are in order of right ascension. A couple of supplements to the NGC were produced; the objects in these catalogues have designations beginning with IC, "Index Catalog". Nearly all the M objects, a little over a hundred in number, also have NGC designations (which run into the 7000s). -- Odysseus
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#3
September 20th 03, 11:26 AM
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Zarkovic wrote:
Why are some galaxies called M(some number) and NGC(some number)? What's the difference and what does each initial or letter represent? Thank you. Just to add a couple of points to what Rick said: Both the Messier and NGC catalogues include many objects within our own galaxy -- planetary nebulae, diffuse nebulae, galactic clusters, and globular clusters -- as well as external galaxies. Messier's initial motivation for compiling his catalogue was to list the permanent "fuzzies" that might be mistaken for passing comets. The M objects are in no particular sequence except that in which Messier happened to observe them (the last few were added by later observers), but the NGC numbers are in order of right ascension. A couple of supplements to the NGC were produced; the objects in these catalogues have designations beginning with IC, "Index Catalog". Nearly all the M objects, a little over a hundred in number, also have NGC designations (which run into the 7000s). -- Odysseus
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