DO27:^ MARTING
ERMANO;^ SKETC
H:^SUE^ FRENCHNo NGC
Clusters
Look beyond the pages of
the classic catalog to fi nd
these star clusters.M
ost of the star clusters we amateur
astronomers observe are included
in the famed New General Catalogue of
Nebulae and Clusters of Stars (NGC),
but that compilation includes no object
discovered after 1887. Since then many
more clusters have been found that
are well within the reach of backyard
scopes, so let’s visit some of these oddi-
ties in the world of open clusters and
learn who found them.
Our featured deep-sky wonders dwell
within the realm of the all-sky chart
at the center of this magazine, but
since we’re just entering the celestial
bailiwick of open clusters in June, they
congregate east of the centerline. I’ll
introduce our quarry from west to east
so that each succeeding cluster climbs
higher as you eyeball the one before.
In case you prefer to stalk clusters by
constellation, that info is given in the
table on page 56.
In 1961 Madona Dolidze published
lists of possible clusters noted during
her spectral studies at the Abastumani
Astrophysical Observatory. These groups
seemed to hold either stars with a
cluster-like distribution of spectral type
versus brightness or else hot young stars
with similar magnitudes.
Dolidze 27 in Ophiuchus is a sparse
cluster, but I’m fond of it anyway. It
brings to mind a simplifi ed version
of the Gemini stick fi gure drawn on
many charts. My 105-mm refractor
at 17× shows a shallow curve of threestars that’s easy to
spot 1.6° north of
Zeta (ζ) Ophiuchi
in the same fi eld
of view. At 76× the
northernmost star in
the curve glows orange
and lies just outside the
northwestern border of the
group’s nominal 25′ span. The other
two stars belong to Do 27 and mark the
heads of the mini-Gemini twins, the
western one yellow and the eastern one
orange. The sketch illustrates the fi gure
as seen in my mirror-reversed view.
Robert Trumpler published a study
of open clusters in 1930, including
37 anonymous groups that were later
named for him. The following year Per
Collinder produced a catalog of open
clusters. The vast majority were previ-
ously known, but all now bear Collinder
designations.
Our next two objects come from
these catalogs. The overlapping clusters
Collinder 316 and Trumpler 24 are
fascinating to skygazers mostly because
they make up the curved tail of the
False Comet. This remarkable object is
nicely visible to the unaided eye when
gazing across the ocean from the Florida
Keys, but various observers interpret it
in different ways. For some the bright
and tight cluster NGC 6231 forms the
pseudo-comet’s head, while others see
it as Zeta^1 and Zeta^2 Scorpii. No matter
which strikes your fancy, you’ll fi nd54 JUNE 2019 • SKY & TELESCOPE
the tail fanning out to the northeast.
With binoculars I’ve been able to enjoy
the “comet” brushing the horizon even
from the northern Adirondack Moun-
tains at a latitude of 44.4°N.
The origin of the term False Comet is
something of a mystery. Some propose
that it was so dubbed by John Herschel,
largely to commemorate his ship’s
landing in False Bay, South Africa, near
which he conducted observations of
the southern sky. Others claim a more
recent origin by amateur astronomers
based solely on appearance. There’s
some evidence S&T Contributing Edi-
tor Alan Whitman inspired the name
by pointing out the “comet-like Milky
Way patch in southern Scorpius” at the
1983 Texas Star Party. Others think the
term may have been coined by Southern
Hemisphere observers.
Resting 27′ northeast of the 4th-
magnitude star 45 Ophiuchi, Trum-
pler 26 is a fi ne cluster through my
130-mm refractor. At 23× four brighter
suns, laid out like the hub and tips of a
three-bladed propeller, overlay a grainy
backdrop of threshold stars. At 164×JUNE 2019 OBSERVING
Deep-Sky Wonders by Sue French
tpThe open cluster
Dolidze 27 seems almost
bereft of stars, but its
brighter members form
a Gemini-like asterism.
The sketch illustrates the
fi gure as shown in the mirror-
reversed view through the
author’s 105-mm refractor.NNEE