The Caldwell Objects

104 & 106
tor of Cordoba Observatory in Argentina,
bestowed the Greek letter Xi (ξ) to the cluster in
his 1879 Uranometria Argentina. This moniker was
not universally adopted, though — which is
unfortunate, since "Xi Tucanae" would complement
"Omega Centauri" nicely. To this day
Tucana does not have a star labeled Xi. The name
47 Tucanae refers to the Flamsteed number of the
"star", and NGC 104 is the only non-stellar nakedeye
object to bear such a number.
It's a shame Lacaille didn't spy 47 Tucanae
with an instrument larger than his ½-inch 8x
telescope. What a missed opportunity to look into
the eye of God. Dunlop observed the cluster with
a 9-inch f/12 reflector and described it as "a
beautiful large round nebula, about 8' diameter,
very gradually condensed to the centre. This
beautiful globe of light is easily resolvable into
stars of a dusky colour. The compression to the
centre is very great, and the stars are
considerably scattered south preceding and north
following [to the southwest and northeast]."
John Herschel called 47 Tucanae "the great
cluster preceding the Nubecula Minor [the
SMC]." With his 18¼-inch f/13 speculum-mirror
telescope, he estimated the diameter of the
cluster's denser portion as 5' and called it
"excessively compressed." Herschel also saw the
cluster's innermost stars shining with a rosecolored
tint while the outliers were pure white.
Agnes Clerke, in The Sphere of the Stars (1905),
deemed Herschel's color perception rather
subjective. "To the present writer, in 1888," she
penned, "the sheeny radiance of this exquisite
object appeared of uniform quality from centre to
circumference. . . . Perhaps no other cluster
exhibits an equal degree of compression. . . . it
was, indeed, for several nights after his arrival in
Peru, mistaken by [Alexander von] Humboldt for
a comet."
Is it only in modern times that we are able
414
to comprehend the beauty of this object? In my
estimation, no other globular in the heavens, not
even Omega Centauri, can compare. Seeing 47
Tucanae through a telescope is like cracking open
a geode and finding it filled with gold dust. It
calls to mind Robert Frost's poem, "All
Revelation":
But the impervious geode
Was entered, and its inner crust
Of crystals with a ray cathode
At every point and facet glowed.
To the naked eye 47 Tucanae shines singularly
at 4th magnitude, like the head of a tailless
comet sailing 2½° west of the SMC. And there is
nothing in the sky background to interfere with
the view of these two splendid objects. They are
like two vessels alone in the void. Under dark
skies there is almost no taking your gaze off
them, so splendid they are together. Seen
through 10x50 binoculars, 47 Tucanae
immediately captures the imagination. Here is a
starlike nucleus surrounded by a halo of soft,
pearly light. In no other globular do I recall
having seen such an opalescent hue through so
small an instrument. My first telescopic view of
47 Tucanae was through the Carter Observatory's
9-inch Cook refractor in 1981; it stole my breath.
The cluster literally burned from within. A tight
2.8'-wide bead of topaz light sizzled like an
electric flame while thousands of sparks
illuminated sphere upon sphere of starlight,
which diffused outward from the cluster's center.
Photographs reveal several million stars — as
many as can be found in some minor galaxies —
across the cluster's 50'-wide disk, but it seemed to
me that there were millions of stars in the tiny
core itself. (Of course, this begs the question: are
all globular clusters the products of merging
minor galaxies?) Omega Centauri lacks 47
Tucanae's awesome central blaze, which draws
Deep-Sky Companions: The Caldwell Objects