Sky and Telescope - March 2016 - 56

OBSERVING

Deep-Sky Wonders

POSS-II / STSCI / CALTECH / PALOMAR OBSERVATORY

NGC 2420

Open cluster NGC 2420 and asterism O'Neal 9 lie about 39′ apart, so at low
power you should be able to ﬁt them in the same ﬁeld of view. Boost your magniﬁcation to resolve individual stars in the cluster.

About 2.9°° south-southwest of Kappa we ﬁnd the
interesting juxtaposition of NGC 2420 and O'Neal 9, an
open cluster and an asterism. My 130-mm scope at 23×
presents NGC 2420 as a fetching swarm of star motes
set against a mist of unresolved stars stretched northnorthwest to south-southeast and enshrined in a pretty
starﬁeld. Boosting the magniﬁcation to 63× enhances
the richness of the cluster and exposes O'Neal 9 in the
same ﬁeld of view, 39′ to the east northeast. The asterism displays only three 11th-magnitude stars in a 3′-long
line tilted north of east and two 9th-magnitude stars
south of center and fairly close together. Examining
NGC 2420 at 102×, I count 30 stars in a 6′-long collection
entangled in haze.
NGC 2420 is quite beautiful through my 10-inch
reﬂector at 187×. Some of the brighter stars outline a circle with a ring around it, reminding me of Saturn. This
pattern overlies a wealth of very faint to extremely faint
stars. The cluster's core is about 5′ across with a concentrated center, but the more sparsely populated fringe that
mantles this core nearly doubles the cluster's diameter.
O'Neal 9 is a cute, boxy group of ten stars spread over a
little more than 3′. Fortunately for me, NGC 2420 and
O'Neal 9 are both detectable in the scope's 9×50 ﬁnder.
When I last observed the pair, it was so gusty that the
wind kept pushing my scope away from them.
William Herschel discovered NGC 2420 in 1783
with an 18.7-inch reﬂector that used a speculum metal
mirror. He logged it as a "Cluster of stars very beauti56

March 2016 sky & telescope

NGC 2266

PETER SPOKES / ADAM BLOCK / NOAO / AURA / NSF

O'Neal 9

ful and close." Herschel adds that he counted at least
50 stars and suspected perhaps double that number.
O'Neal 9 was found in 2005 by California amateur Mike
O'Neal with a 16-inch reﬂector at 98×. It's included as
an asterism in the database of the Deep Sky Hunters, a
Yahoo group. Many such asterisms were spotted by DSH
members as a by-product of their search for previously
uncataloged open clusters.
Open cluster NGC 2331 lies halfway between Tau
(τ) and Omega Geminorum. In my 130-mm refractor at 37×, its suns form a striking starburst array, like
an explosion frozen in a moment of time. The pattern
slightly overspills the cluster's given 19′ size. At 48× I
count 22 stars, 10th magnitude and fainter, within the
19′ boundary.
While NGC 2331 consists of loosely scattered stars,
NGC 2266 to its west is wonderfully crowded. Look for
this little gem 1.8° north of Epsilon (ε) Geminorum.
With my 130-mm scope at 23×, it looks like a fan-shaped
comet with a star at the head (south-southwest) and a
fainter one on the southeastern side. At 102× an arc of six
stars beads the southeastern side, the bright one burning yellow. The wedge of haze tapering north-northwest
from the arc is densest in the middle of its western side
and dotted with about 15 very faint stars. A few stars
shelter on the arc's opposite side, but the entire group
covers only 5′. At 164× NGC 2266 sports 27 stars in total.
This is a charming cluster in my 10-inch scope at 166×,
harboring a splash of 45 diamond-chip stars.
NGC 2266 brings our tour to a delightful ﬁnish for
visual observers, yet it's also a grand and colorful target
for those who do deep imaging during starry nights.
Why not give it a try? ✦

In a somewhat crowded star ﬁeld, the arc of six colorful gems
on the southeastern side of open cluster NGC 2266 stands out.

Sky and Telescope - March 2016

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