Expert: Tom Whiting - 2/13/2008

Question
hello tom,
how are the galaxies and celestial objects named. in 'm41' what does 'm' and '41' represents.
thanking you
bithu

Answer
Hello bithu,
Sorry but M-41 is not a galaxy...it is an open star cluster in
Canis Major (Big Dog) about 4 degrees due south of Sirius, the Dog
Star (and brightest real star in our night sky).  M-41 is barely
a naked eye fuzzy spot in a very dark, moonless sky.

And, Oh, it's not m41, it's M-41...always use the capital letter M
for all the Messier objects.

But now to your question.....Early astronomer Charles Messier, (1730-1817) a French astronomer, was an avid comet hunter with his little
telescope, but he was frustrated when he ran into little fuzzy
spots in the sky that didn't move from night to night, thus not a
comet.  So he started his "list of non-comets" or list of avoidance
objects, starting with M-1.  Then continuing M-2, M-3 and so on
all the way up to M-110.  Thus, there are 109 Messier objects in our
night sky for us to observe.  Why 109 when they are numbered from
1 to 110?  Because of a Messier error, M-102 was a duplicate observation of M-101.  So while Charles Messier discovered about
a dozen comets in his lifetime, he is most famous for his "list"
of avoidance objects, which today we know are the brightest and finest galaxies, open star clusters, nebulae, and Globular star clusters (Deep Sky Objects, or DSO's by another name) in our night sky.  So now you know the rest of the story.

{If Messier were to come back to life, I'm sure he would be very
surprised that he is famous, not for his comet discoveries, BUT
his avoidance list!! They are the best DSO's in the night sky for
us to observe!!}

Oh, there was no rhyme or reason to his DSO discoveries; they are pretty much numbered randomly scattered all over the Northern Hemisphere night sky....Oh, and just one supernovae cloud
remnant, M-1 in Taurus.  M-2 is a globular star cluster in Aquarius,
M-3 is a globular in Canes Venatici, M-4 is a globular in Scorpius,
M-5 is a globular in Serpens, M's 6 and 7 are open star clusters in
the tail of the Scorpion, M-8 is the Lagoon Nebula in Sagittarius, and so on. So see, there is no systematic approach here...you just have to memorize them, and their location in the night sky.  This
is one of the first things that a new amateur astronomer does once
he/she learns their constellations. (area's of the sky).
Then next fainter and smaller DSO's are the nearly 7800 NGC (New General Catalogue) deep sky objects, which are typically dimmer and farther away, but that's another story. (And most of us advanced amateurs with large scopes know where most of those are at too, once you've been doing this for 10 or 20 years.)   
Oh, for a fine biography on Charlie Messier, see
http://www.messiermarathon.com/about.htm

Hope all this helps,
Clear Skies,
Tom Whiting
Erie PA  USA

PS...Oh, his first real galaxy discovery wasn't until number M-31,
the great spiral galaxy in Andromeda, which is actually naked-eye
in a dark sky.  Then M-32 was a companion galaxy to M-31, then
M-33 was the Pinwheel Galaxy in Triangulum. His next galaxy discovery
wasn't until M-49 in Virgo.  And also realize, to Messier, these
were all just fuzzy spots in his little scope.  He had no idea
(like we do today) exactly what they were, how big, or how far away.
To him, they were all just "nebulosities".  Back then, there was not
yet the distinction between galaxies, open clusters, nebulae, or
globular star clusters, like there is today.  In fact, the word
"galaxy" didn't come into existence until the 1920's with Edwin
Hubble's work, but that's still another story.
Clear Skies,
Tom W.

FOLLOW UP:
So every Deep Sky Object has either a Messier Number, or an NGC
number...that's how they were named.  Some objects however, over the
years have also been designated a "nickname", sometimes just due to
their appearance in the sky or on photographs.  Thus, we also call
M-8 the Lagoon Nebula and M-16 the Eagle Nebula, M-11 the Wild Duck
Cluster, M-97 the Owl Nebula, M-51 the Whirlpool Galaxy, M-64
the Black Eye Galaxy, M-104 is the Sombrero Galaxy, and so on.
This even extends to some NGC objects as well, as NGC 6543 is the Cat Eye Nebula and NGC 2392 is the Eskimo Nebula, and NGC 6826 is the Blinking Planetary Nebula. So that's how it works until you
get down to the very very faint galaxies, then you go to other
catalogues like the UGC (Uppsula general catalog) and MGC catalogs,
and so on....getting deeper and deeper (read that fainter and fainter galaxies).  So that's how it works.
Clear Skies,
Tom