The Caldwell Objects

25
distance, the fact that it shines as brightly as 10th
magnitude suggests that the cluster has a high
intrinsic luminosity. Indeed, images taken with
large telescopes reveal a wealth of stars packed
into a tiny disk only 4.6' across. The brightest
members shine individually with an apparent
magnitude of 17.3 on average, while the far more
numerous horizontal-branch stars (so called for
their locations on a color-magnitude diagram)
each shine at an apparent magnitude of 20.4 on
average. So don't expect to resolve much in the
way of stars once you locate this mysterious
object. John Herschel didn't, it seems; on March
18, 1831, he called NGC 2419 simply "not very
bright, large, pretty much elongated."
NGC 2419 lies about 7° north-northeast of
the magnitude-1.6 star Castor, the secondbrightest
star in Gemini and a stunning multiplestar
system for reasonably sized (or unusually
sharp) telescopes. The cluster is nestled a mere 5'
east of two similarly bright stars, the
westernmost of which is a fine 8th-magnitude
double itself. (These stars are visible in the
photograph on page 104). When I first searched
the area using the 4-inch at 23x I made the
mistake of looking for a small, concentrated glow
and swept past the cluster several times. I did the
same at 72x. Just when I was about to give up for
the night, my eye caught sight of an extremely
dim patch of light
next to the easternmost of the two stars mentioned
above. I immediately returned to 23x and
had no problem seeing this diffuse mote of light
because I knew exactly where to look.
At low power the cluster looks ethereal, like
a dim and distant comet whose ices are just
beginning to sublimate. At 72x the globular
appears as a weak circular glow, largely uniform
but with some suggestion of a central brightening
and an irregular outer shell. The longer I looked
at the cluster with 72x the more prominent and
intriguing it became, though I discerned no
further details. Higher power added little to the
scene. Amateurs using telescopes in the 10-inch
range might hope to see some patchiness toward
the cluster's center, but little else. The object is a
challenge for a 4-inch telescope under dark skies,
so light pollution will probably render it
invisible. That being said, don't let the fact that
this cluster is so dim discourage you from trying
to locate it. The object's beauty lies not in its
appearance but in its distance. Without question
NGC 2419 is the most distant globular cluster that
can be seen with modest telescopes. AM 1 and the
Palomar ("Pal") globulars are much too dim to be
viewed with such instruments. However, these
latter clusters are favorite challenges for amateurs
using 24- to 40-inch reflectors at the annual Texas
Star Party and other gatherings.
106 Deep-Sky Companions: The Caldwell Objects