The Caldwell Objects

times larger than the full Moon. In other words,
take the light of a 6th-magnitude pinpoint of light
and smear it out across 40' of sky — against the
Milky Way, no less. Now consider that none of
the cluster's 100 known members shine brighter
than 9th magnitude. NGC 6124 is one of those
objects that can take you by surprise under a dark
sky, for it is not immediately obvious to the
naked eye, but if you happen to be lying back in a
chaise longue and admiring southern Scorpius
for aesthetic reasons, you might find yourself
springing up convinced that you've just
discovered the large, diffuse head of a naked-eye
comet. And so it was in the 18th century when
Louis de Lacaille came across this object from the
Cape of Good Hope — not with his unaided eye
but with his ½-inch 8x telescope. "It resembles a
big comet without [a] tail," he wrote, adding it to
his list of Class I objects ("nebulae without stars").
Some catalogs credit James Dunlop with the
object's discovery, since he was the first to
describe its true nature: " round A cluster of small
stars of nearly equal magnitudes, about 12'
diameter, considerably congregated to the centre,
not rich in small stars. . . . [T]here is no nebula."
Dunlop listed the cluster as the 514th object in his
1827 catalog, but credit for its discovery
75
should really remain with
Lacaille.
When I first saw NGC
6124 I did jump up with a
start. While observing the
cluster with 7x35
binoculars on September
9, 1996, I noticed not one,
but two, objects: a large,
round haze some 20' in
diameter and another
round haze separated
from the first by a nar
row lane of darkness. The two glows lay to the
northeast and the southwest. I tried to identify
the two glows on star charts but found only one:
NGC 6124. " comet!" A flashed through my mind.
Clouds began moving in, so I went to the 4-inch
and confirmed the existence of an ill-defined
patch of light northeast of the main cluster before
clouds covered the sky. That night many
thoughts went through my mind. Is this how
Lacaille felt when he first encountered NGC
6124? Much like Lacaille, I was using the rough
equivalent of a ½-inch instrument at 7x. And,
like him, I had chanced upon a large "nebula"
that appeared to lack stars. Perhaps, I thought,
this secondary haze was part of NGC 6124. But if
that were true, why did Dunlop and some
modern-day observers call the cluster "round"
instead of "irregular," or "dumbbell shaped," or "a
double cluster forming a figure-eight pattern"? I
checked various sources for the size of NGC 6124
and all agreed that it was between 20' and 29',
which placed the secondary fuzzy oval only
partly inside the established object's perimeter.
The next night fell clear, so I checked the
object for movement but found none. It wasn't a
comet. Figuring the entire sky had been covered
well enough by now for a new cluster's discov-
The Caldwell Objects 297