The Caldwell Objects

68
68
R Coronae Australis
Nebula
NGC 6729
Type: Emission and
Reflection Nebula
Con: Corona
Australis
RA: 19 h 01 m 54 s
Dec:-36° 57. 1’
Mag: -9.5 (O'Meara);
variable
Diam: 1.3'; variable
Dist: 424 light-years
Disc: Albert Marth, listed in his
Catalogue of 600 new
nebulae, published in 1876 in the Memoirs of the Royal
Astronomical Society, Vol. XXXVI
H ERSCHEL: None.
OUT OF CURIOSITY ONE NIGHT IN SEPTEMBER
1996,1 put a low-power eyepiece into my Genesis
and swept its 4-inch glass across the northeastern
corner of Corona Australis, the Southern Crown,
just below the Teapot aster-ism in Sagittarius. I
was pretending to be Charles Messier hunting for
comets. I wanted to see if Messier would have
picked up the R Coronae Australis Nebula
(Caldwell 68). Of course, Messier's instrument
would not have been as good as mine, so I took
that into account. I also chose to ignore the fact
that this region was simply too far south for him
to observe. But had he observed from a more
favorable latitude, I wondered, what would he
have found here? Remember, Messier was not
looking for faint nebulae; he was looking for
comets. Without question, the father of comet
hunters would have noticed the 7th-magni-
270
GC: None.
NGC: Variable star (11th magnitude and fainter) with nebula.
tude globular cluster NGC 6723 in Sagittarius; it
lies only 30' northwest of our target. (Surprisingly,
this stunning object failed to make it
into the Caldwell Catalog.) It's possible that the
great comet hunter would have noticed the close
7th-magnitude double star at the core of the
nebula IC 4812, a little more than 10' southwest of
R Coronae Australis; the pair's tightness makes it
look fuzzy, like M40 in Ursa Major, so its
character probably would have piqued Messier's
curiosity. And it's also possible, though unlikely,
that Messier would have noticed the faint double
nebula NGC 6726-7 just 5' northwest of our
target. But I'm certain Messier would have
missed our Caldwell object—a "little" star with a
"tail" — because it simply would have been too
inconspicuous for this man with a mission.
Not that the nebula isn't visible in a small
Deep-Sky Companions: The Caldwell Objects