FEBRUARY 2020 OBSERVING
Deep-Sky Wonders
56 FEBRUARY 2020 • SKY & TELESCOPE
stars emerge. NGC 2186 is an attrac-
tive cluster in my 10-inch refl ector.
At 70× the brighter stars are crowded
by many sparkly pinpoints of light.
At 118× the yellow star closely guards
a distinctive line of stars trailing
northward from the pair. Together they
dominate the northeastern region of a
20-star wedge tapering southwest for
4½′. The yellow star is thought to be
a giant of spectral type G0 and a true
member of the cluster.
At low power, NGC 2186 shares the
fi eld of view with the open cluster NGC
2180. Through the 130-mm refractor
at 23×, I see an 8th-magnitude star sur-
rounded by a bunch of faint suns in a
starry fi eld. At 63× the faint stars seem
to form a hook wrapped around the
bright one, as though they were trying
to yank it offstage to the east. The hook
is about 8½′ long and 4½′ wide, but it’s
only the south-southwestern part of a
splashier group of 55 stars spanning 20′.
The split personality of NGC 2180
is refl ected in the various catalogs and
atlases that include it. Some show the
cluster as a small group centered on the
8th-magnitude star, while others have it
as a much larger group centered farther
northeast. Our table refl ects the size
and position from the 2005 Catalog of
Open Cluster Data (Kharchenko et al.).
Our fi nal target, NGC 2184, is
larger and showier than its neighbors
to the north. It lies 8.4° south of NGC
2180 and 34′ west-northwest of a deep-
yellow, 5.8-magnitude star. The 130-
mm scope at 23× shows a loose col-
lection of 30 stars, magnitude 7.8 and
fainter, splashed across 32′. A lopsided
pie wedge of four bright stars domi-
nates the southeastern side of the clus-
ter, all but the faintest one in shades
of yellow. The middle star in the arc of
the pie crust is the lovely double Struve
874 (Σ874), its 8th-magnitude primary
closely attended on the north- northwest
by a 9th-magnitude companion. Someof the cluster’s lesser gems also glitter
with yellowish hues.
In the 1973 Revised New General
Catalog (Sulentic et al.), NGC 2184
was deemed nonexistent because Jack
Sulentic couldn’t verify it on the 1950s
National Geographic Society – Palomar
Observatory Sky Survey prints. How-Clusters, Doubles, and a Nebula
in Northern Orion
Object Type Mag(v) Size/Sep RA Dec.
NGC 1662 Open cluster 6.4 20 ′ 4 h 48.5m +10 ° 5 6′
Alessi 29 Cluster remnant? — 10 ′ 4 h 49.4m +10 ° 41′
Elosser 1 Asterism — 21 ′ 4 h 50.9m +7° 51′
Rho Ori Double star 4.6, 8.5 6.9′′ 5 h 13.3m +2° 52′
32 Ori Double star 4.4, 5.8 1.3′′ 5 h 30.8m +5° 57′
Cr 69 Open cluster 2.8 70 ′ 5 h 35.0m +9° 56′
Sh 2-264 Emission nebula 4.0 6.5° 5 h 36.3m +9° 58′
NGC 2186 Open cluster 8.7 5.0′ 6 h 12.1m +5° 28′
NGC 2180 Open cluster — 22 ′ 6 h 09.8m +4° 49′
NGC 2184 Open cluster 5.8 33 ′ 6 h 11.7m –3° 36′
Angular sizes and separations are from recent catalogs. Visually, an object’s size is often smaller than
the cataloged value and varies according to the aperture and magnifi cation of the viewing instrument.
Right ascension and declination are for equinox 2000.0.ever, clusters are sometimes over-
whelmed by fi eld stars on deep images,
while our eyes do a better job of sorting
them out.¢ Contributing Editor SUE FRENCH
wrote this column for the February 2012
issue of Sky & Telescope.POSS-II / CALTECH / STSCI / PALOMAR OBSERVATORYNGC 2186NGC 2180