The Caldwell Objects

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mining other stars' absolute magnitudes. Within
the last quarter century that distance was refined
to 42 light-years. More recently, the Hipparcos
satellite determined that Beta Trianguli Australis
lies 40 light-years from Earth. The Milky Way
runs through the constellation, enriching it with
faint stars.
From a dark-sky site, NGC 6025 stands out
to the naked eye as a puff of soft light. It lies 1°
due east of a tight arc of three 6th-mag-nitude
suns oriented north-south. The cluster's brightest
star shines at magnitude 7.1, so it is a good
naked-eye challenge. Note that in the table on
page 381, my naked-eye estimate of the cluster's
appar
ent magnitude is 0.4
magnitude fainter than
Brent Archinal's published
value. But the
cluster culminates only
about 10° above the
horizon from Hawaii, so
I encourage observers in
the Southern
Hemisphere to estimate
its naked-eye brightness
under more reliable
conditions.
In 7x35 binoculars
NGC 6025 looks
like a dagger, with a row of three stars surrounded
by an elongated halo of unresolved
suns. And this is exactly what Nicolas Louis de
Lacaille saw when he discovered the cluster with
his ½-inch 8x telescope. In his 1755 catalog he
describes NGC 6025 as "three faint stars in line
with nebulosity." (Seen this way, the cluster
resembles Carolyn Shoemaker's famous lupitersmashing
"squashed comet," Comet Shoemaker-
Levy 9, for it looks like a fragmented comet
nucleus shrouded in a coma of scintillating dust.)
James Dunlop observed the
382
cluster on five occasions and saw no nebulosity.
He described it as a "group of about twenty stars
of mixt magnitudes, forming an irregular figure,
about 5' or 6' long . . . and there is no nebula in
the group of stars except what is common in the
neighbourhood." (Lacaille's nebulosity, of course,
was just the haze of unresolved starlight.) The
Rev. T W . Webb . simply called the object a
"brilliant cluster."
With north up at 23x in the 4-inch, the
cluster's dozen or so brightest stars form the
Greek letter χ. The brightest star resides in a
Deep-Sky Companions: The Caldwell Objects