The Caldwell Objects

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which is best seen with high magnification.
From a dark-sky site the cluster appears to be
snared within a web of dark nebulosity. Throw
the low-power image slightly out of focus and
see if the region southwest of the pyramid
appears especially dark. Perhaps a dust cloud
has dimmed starlight here.
At 72x the cluster fractures into smaller
groupings, even as the pyramid remains bold
and bright. The pendant containing HD 111973
reveals at least seven stars that form a smaller
pyramid at right angles to the larger, brighter
one. HD 111973 looks yellow at 72x, as does HD
111904, the magnitude-5.8 star at the
northwestern corner of the large, bright pyramid.
In February 1997 and again in April 2000, HD
111973 appeared at least a half magnitude (60
percent) brighter than HD 111904 to my eyes —
even though, according to the second edition of
Sky Catalogue 2000.0, it should be 0.1 magnitude
(10 percent) fainter. An undated drawing by
Kenneth Glyn Jones in Volume 7 of the Webb
Society Deep-Sky Observer's Handbook (published
in 1987) shows HD 111973 signifi-candy fainter
than HD 111904, and this observation was based
on a view through a 12-inch reflector. Most
photographs I've seen show HD 111973 fainter
than HD 111904, but that may be an artifact of
the photographic emulsions. (Note, by the way,
that in both Ernst Hartung's and Robert
Burnham Jr.'s handbooks the photographs of the
cluster have been flopped, with east and west
reversed.) Clearly these stars warrant watching.
At 72x in the 4-inch SAO 252073 looks more
orange than red to me. It is the northeasternmost
star in a tiny line of three similarly
bright stars oriented northeast to southwest.
SAO 252073, to my eyes, is the faintest of these
three stars. Glyn Jones, however, saw it as the
brightest. My eyes tend to be blue-sensitive
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while other observers are more sensitive to red
light, so this apparent discrepancy might be
related to the way different observers perceive
color, and not to any real brightness variations.
Yet Edward James Stone, Her Majesty's Astronomer
at the Cape from 1870 to 1879, suspected
that this red star had altered its brightness since
John Herschel had observed it. And the Hipparcos
satellite's database seems to support the
notion, for on its watch the star's apparent visual
magnitude appears to have ranged from 7.08 to
7.52. However, Hipparcos didn't enable
astronomers to determine a period of variability
or to classify the star's light curve. Clearly it
would behoove someone with a photometer to
monitor all the Jewel Box's supergiant suns for
variability.
Moderate magnification reveals other
treasures in the Jewel Box. The brightest stars to
the southwest of the large pyramid form two
semicircles, like wide crowns, facing in opposite
directions: one opens to the north-northwest and
the other to the southeast. Immediately south of
these crowns is a long chain of fainter suns
oriented in the same northwest-to-southeast
direction as the two semicircles. The void
between these groupings may be a long lane of
dust.
At high power the cluster fractures completely
and the Jewel Box loses its luster. Most
prominent is HD 111973 and the pyramidal
pendant. Look for a black cross at the southwestern
edge of the pyramid. Look also for a
tight double star immediately northwest of HD
111973 and another about 2' to the southeast. For
a slightly greater challenge, see if you can detect
a red, 13th-magnitude star south of SAO 252073.
It is one that John Herschel first noticed, along
with so many others of the Jewel Box's sparkling
gems (though he didn't say how far south of SAO
252073 it is).
Deep-Sky Companions: The Caldwell Objects