The Caldwell Objects

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NGC 5823
Type: Open Cluster
Con: Circinus; Lupus
RA: 15 h 05.4 m
Dec: -55° 36'
Mag: 7.9
Diam: 12.0'
Dist: 3,400 light-years
Disc: John Herschel, 1836
J. H ERSCHEL: [Observed
between 15 and 20 April 1836]
Cluster class VII; a fine large
cluster of separate stars [of] 13
[th to] 14th magnitude, 10'
diameter; not much
compressed in the middle;
nearly fills the field, (h 3589)
GC/NGC: Cluster, considerably large, rich, little compressed in
the middle, stars of magnitude 13 to 14.
O PEN CLUSTER NGC 5823 is ONE OF THE few
Caldwell objects with dual celestial citizenship.
Although its center (as tabulated by Brent
Archinal) lies just within the border of Circinus,
the Drawing Compasses, its northernmost stars
belong to Lupus, the Wolf. John Herschel found
it "a fine large cluster." Others have exclaimed
that it is "rich" and "exuberant." But observers
beware: you may have difficulty finding the
cluster or verifying its presence in your eyepiece's
field of view. But once that's achieved, the cluster
becomes a sight well worth pondering. So first
let's get you there.
Finding the area containingNGC 5823 is a
c a k e First w a draw l k an . imaginary line between
zero-magnitude Alpha (α) Centauri (Rigil Kentaurus)
— the brighter of the two stars pointing
to the Southern Cross — and 3.4-magnitude Zeta
(ζ) Lupi 10° to the north-northeast. Now use your
binoculars. Locate Zeta Lupi, then move 2½°
along that line to the southwest (that is, back
toward Alpha Centauri). Do you see a large
circular "smoke patch" filled with faint, glittering
suns? This is the 5th-magnitude open cluster
NGC 5822 in Lupus. It spans an impressive 40'. If
you're under a dark sky, lower your binoculars
and look for this cluster with the unaided eye;
you should be able to detect it. Our Caldwell
target, NGC 5823, is 3 magnitudes fainter, lies
about 1¼° farther south, and is in a dense, patchy
region of the Milky Way. So it's easy to imagine
all manner of clusters around it. In binoculars
NGC 5823 should appear as if it were a dim,
detached segment of
348 Deep-Sky Companions: The Caldwell Objects