The Caldwell Objects

2000.0 (second edition), Uranometria 2000.0, and
the Millennium Star Atlas all depict it as a nebula
and a cluster, and it is described as such in NGC
2000.0 and in the Observing Handbook and
Catalogue of Deep-Sky Objects. But, as Brent
Archinal of the U.S. Naval Observatory notes,
NGC 281 is not a star cluster. Rather, he explains,
it is the nebulosity associated with the star cluster
IC 1590. NGC 281 was an Edward Emerson
Barnard discovery, while IC 1590 was discovered
later by Guillaume Bigourdan. "In any case,"
Archinal writes, "Bigourdan . . . clearly stated
these two were not the same object. Therefore the
correct name for the cluster is IC 1590."
Archinal notes a further complication —
namely, that the Deep Sky Field Guide to
Uranometria2000.0lists NGC 281 and IC 1590 as
two distinct open clusters at different positions,
while Sky Catalogue2000.0 asserts, in its Open
Cluster Cross Index, that NGC 281 and IC 1590
are the same object. That confusion aside, the
nebula (NGC 281) is quite an obvious irregular
patch of glowing gas a mere 1¾° east of Alpha
(α) Cassiopeiae (Shedir); its Moon-sized glow
forms the apex of a triangle with Shedir and Eta
(η) Cassiopeiae and is visible in 7x35 binoculars
under a dark sky. It's easily picked up in a sweep
with the 4-inch at 23x. At first glance the nebula
has a cometlike quality to it, but once you focus
your attention on it, the small cluster (IC 1590)
embedded within it draws in your attention. The
cluster sports 90 stars within its tiny disk, with
the brightest being the magnitude-7.8 triple star
HD 5005, which contributes most of the
ultraviolet light that powers the nebula. Archinal
suspects many more of the stars that appear
within the nebula may be associated with the
cluster.
432
4
N G C 5 8 6 6
T y L p e n : G t a i l ( c a S x u O y l ) a r
C o D n r : a c o
RA: 15 h 06.5 m
Dec: +55° 46'
Mag: 9.9
SB: 12.6
Dim: 7.3' x 3.5'
Dist: 50 million light-years
Just 4° southwest of Iota (ι) Draconis, or Edasich,
lies a remarkable lenticular galaxy seen almost
exactly edge on. In long-exposure photographs
NGC 5866 sports a very bright ring and a
prominent dust lane, which are slightly tilted
with respect to one another and to the equatorial
plane of the galaxy's central lens — making each
side of the galaxy look like a pair of slightly
opened scissors. X-ray emission has been
observed along the galaxy's major axis, as has
ionized gas. Early photographs overexposed the
dust lane, leading astronomers to misclassify this
lenticular system as an elliptical galaxy. NGC
5866 may contain a considerable 1 trillion solar
masses or thereabouts. Assuming its estimated
distance of 50 million light-years is correct, the
galaxy spans some 90,000 light-years.
Until the late 1990s even the reliable NASA
Extragalactic Database boldly listed NGC 5866 as
Messier 102. So the history behind the mysterious
Μ102, and its questionable relationship to NGC
5866, deserves repeating. In Messier's catalog,
Μ102 is described in the following way:
Nebula between the stars (o) [Omicron] Bootis
and (ι) [Iota] Draconis. It is very faint. Close to
it is a sixth-magnitude star.
Deep-Sky Companions: The Caldwell Objects