The Caldwell Objects

104 & 106
A FIST'S WIDTH SOUTHWEST OF FIRST-tie
easier resolved, rather a brighter white, and
MAGnitude Achernar, the end of the celestial perhaps more compact and globular. This is a
River Eridanus, is the body of one of the sky's beautiful globe of white light; resolvable; the
most "flighty" constellations: Tucana, the Toucan. stars are very little scattered." Dunlop's reference
With an area of 295 square degrees, Tucana is the to "the 2nd of the Connaissance des Terns" was to
sky's 48th-largest constellation; it contains some none other than Messier 2, the second object
80 stars between magnitudes 2.9 and 7. Johann listed in Charles Messier's catalog, which was
Bayer first introduced this colorful bird simply as published in the French almanac Connaissance des
"Toucan" in his 1603 Uranometria; the name was Temps.
later latinized. The Toucan flies around the South NGC 362 lies about 2¼° southwest of gold-
Celestial Pole with three of the heavens' greatest en 4.9-magnitude Kappa (κ) Tucanae and 1½°
wonders dangling from its claws: the Small north-northeast of NGC 346 and NGC 371 — two
Magellanic Cloud (a dwarf galaxy that orbits our large balls of gas and stars on the northern edge
Milky Way) and the globular star clusters NGC of the brighter part of the Small Magellanic
362 and 47 Tucanae (Caldwell 104 and 106, Cloud. In 10x50 binoculars NGC 362 looks like a
respectively).*
slightly out-of-focus star, especially with averted
NGC 362 and 47 Tucanae bracket the Small vision. The cluster shines with an apparent
Magellanic Cloud to the north and west, respec- magnitude of 6.4, and no similarly bright object
tively, so it is only natural that we discuss these competes with it in its immediate vicinity. Under
globulars together. Recent proper-motion studies a dark sky I have seen it with the naked eye.
of these clusters' stars confirm that they belong to Through the telescope its apparent size and
our Milky Way system and are merely projected magnitude recall those of the globular star
against the Small Magellanic Cloud's halo some cluster M2 in Aquarius (as Dunlop himself noted
176,000 light-years away. NGC 362 is the more so long ago).
distant of the two clusters. Indeed, 47 Tucanae is NGC 362 is a relatively metal-rich cluster.
one of the closest globulars to our Sun; it is as far On average, each of its stars has about 1/14 as
from the Sun as is Μ10 in Ophiuchus, though much iron as does the Sun. This is a higher
M10 is about 9,000 light-years closer to the metallicity than that found in most globulars.
galactic center.
Several generations of stars must have preceded
James Dunlop discovered NGC 362 in the the cluster's formation in order to enrich it thus.
1820s. It is the 62nd object in his Catalogue of This suggests that the metal-rich globulars,
Nebulae and Clusters of Stars in the Southern though old, are younger than metal-poor ones.
Hemisphere, Observed at Parramatta in New South NGC 362 also has an overabundance of binary
Wales. Of it he writes, " beautiful A bright round stars and an exceptionally tight core 1.6' (13 light-
nebula, about 4' diameter, exceedingly years) in diameter. Apparently this tight core has
condensed. This is a good representation of the saved the cluster from certain destruction. NGC
2nd of the Connaissance des T [sic] e in figure, r n 362 s is in a highly eccentric orbit that takes it
colour, and distance; it is but a very lit-
within 1 kiloparsec (3,260 light-years) of the
galactic center. Had its core not been so tight, the
*Caldwell-number users beware: 47 Tucanae (NGC 104) is Caldwell 106, cluster probably wouldn't have survived the 100
while NGC 362 is Caldwell 104.
or so encoun-
410
Deep-Sky Companions: The Caldwell Objects