The Caldwell Objects

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tronomer William Harris once wondered if this
cluster might be escaping our galaxy. Indeed,
some models do show it following a hyperbolic
orbit. More research needs to be conducted on
this enigmatic globular's space velocity before the
truth is known.
In a 1996 Astrophysical Journal article, Martha
Hazen (Harvard-Smithsonian Center for
Astrophysics) recounts how she "blinked" eight
reasonably matched pairs of photographic plates
of the cluster but found no candidate variable
stars. This is not surprising, for other metal-poor
globulars share the same trait. Her findings place
NGC 5694 into a group of low-metallicity
globular star clusters with few (or no) RR Lyrae
stars. On average, each member of NGC 5694 has
a spectral class of F4 and 1/70 as much iron as our
Sun. CCD photometry also has revealed the
presence of bright blue quasi-stellar knots very
close to the cluster's core, suggesting the
presence of blue stragglers. NGC 5694 certainly
displays a high degree of central condensation,
with a core measuring a mere 7".
To find the cluster look a little more than 10°
south-southwest of Alpha (α) Librae
(Zubenelgenubi), or about 5½° west-southwest of
3rd-magnitude Sigma (σ) Librae. A little less than
2° east of the globular is a lovely 3½°-long chain
of 4th- to 6th-magnitude stars; it heads southeast
from the star 4 Librae, then bends nearly to the
south at 55 Hydrae before ending at 58 Hydrae.
These stars form the body of the now-obsolete
constellation Noctua, the Night Owl, which
appeared in Elijah H. Burritt's Atlas
accompanying the Geography of the Heavens, first
published in 1833. The owl stands on a branch
that stretches east-west from Pi (π) Hydrae to
Sigma Librae, and the branch includes the stars
50, 51, 52, 58, 59, and 60 Hydrae. As Robert
Burnham Ir. lamented in his Celestial Handbook,
the "loss of this little
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asterism might seem unfortunate to astronomers,
since no other celestial creature so appropriately
honored their profession."
NGC 5694 is part of a bent arrow of fainter
stars that looks like a crooked, l°-long version of
the constellation Sagitta. At 23x in the Genesis the
arrow comprises several dimmer asterisms, so the
field is quite attractive. The
globular is the northernmost "star" in a chain of
suns that winds northward from the brightest
(middle) star in the arrow's shaft; thus the NGC
description, "among stars." In fact, the
foreground stars near the cluster are so tightly
arranged that the area positively glows under
averted vision. This glow should draw your eye
toward the cluster.
At 72x NGC 5694 reveals itself as a very
small, compact glow, and at a glance it looks like
a slightly swollen star. It certainly is not a Hydra-
Hysteria-stopper — unless, as Houston
recommends, it's the last object you view. Its
brightest members shine at magnitude 15.5, and
its horizontal-branch magnitude is a feeble 18.5.
Some field stars do appear to be superimposed
on the cluster. Spend some time with NGC 5694
at moderate power. Do
Deep-Sky Companions: The Caldwell Objects