The Caldwell Objects

19
N G C 6 2 8 1
T y O p e C : n l u s t e r
C o S n c : o r p i u s
RA: 17 h 04.8 m
Dec: -37° 53'
Mag: 5.4
Diam: 8'
Dist: 1,800 light-years
The tail of Scorpius, the Scorpion, is projected
against the hub of our galaxy, a region littered
with open clusters and asterisms. Some might
argue that once you move beyond the Messier
and Caldwell Catalogs, open clusters are all the
same — little puffs of concentrated starlight. But
one, NGC 6281, stands out from the multitude as
a fine target for small telescopes. In fact, at
magnitude 5.4, NGC 6281 is the brightest non-
Messier/non-Caldwell open cluster in Scorpius,
though one hardly hears about it. Brent Archinal
lists about 70 stars within its 8'-wide disk, with
the brightest shining at magnitude 9.0. The
cluster's surface brightness is also quite high,
making it a fine naked-eye target.
Alas, the cluster is near a host of other
popular objects. It is 4½° north-northeast of NGC
6231 (Caldwell 76), 2° southwest of the Bug
Nebula (Caldwell 69), 10° southwest of M7, and
8° northeast of NGC 6124 (Caldwell 75). At least
NGC 6281 is conveniently located. It simply lies
2½° east-northeast of Mu 1,2 (μ 1,2 ) Scorpii, about
one-third of the way toward the paired Stinger
stars at the end of the Scorpion's tail. Through the
Genesis NGC 6281 is best seen at 23x, when its
stars form a marvelous dipper of bright suns
superimposed on a fog of Milky Way. Ernst
Hartung concurs, saying the cluster is "very
beautiful with a pyramidal group of stars . . .
standing out prominently in
the centre; it contains several pairs and two
bright orange stars, and the linear pattern is most
striking." Christian Luginbuhl and Brian Skiff
add that the cluster has "20 stars arranged over
haze like Christmas tree lights," making it "a
pretty cluster" for a 60-mm telescope.
20
SL 7
T y D p a e Nebula r : k
C o L n u : p u s
RA: 16 h 01.8 m
Dec:-41° 52'
Mag: —
Dim: 160' x 10'
Dist: unknown
Our final hidden treasure is an incredible veil of
darkness in southeastern Lupus that dips ever so
slightly into Norma and Scorpius. On a scale of
opacity ranging from 1 to 6, SL 7 is classified as a
6, meaning "highly opaque." The nebula is an
elongated swath of darkness running from eastnortheast
to west-southwest. Though it is about 4
Moon diameters long, only about a dozen stars
between 9th and 11th magnitude lie within its
confines! The darkest section, to the southwest, is
an empty l°-wide corridor that begins about 3¾°
due south of Eta (η) Lupi, just south of a 5thmagnitude
star. Compared to SL 7, the Coalsack
(Caldwell 99) appears very dark to the unaided
eye. Yet through a telescope the Coalsack is
littered with stars; its clouds do not appear black
(like those of SL 7) but gray through the 4-inch.
Twenty Spectacular Non-Caldwell Objects 443