Australian Sky & Telescope - April 2016__

54 AUSTRALIAN SKY & TELESCOPE APRIL 2016

About2. 9 °south-southwest of Kappa we find the

interesting juxtaposition of NGC 2 420 and O’Neal 9,

anopenclusterandanasterism.My130-mmscope

at 23×presents NGC 2420 as a fetching swarm of star

motessetagainstamistofunresolvedstarsstretched

north-northwest to south-southeast and enshrined

inaprettystarfield.Boostingthemagnification

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 centre and

fairly close together. Examining NGC 2420 at 102×,I

count30starsina6′-long collection entangled in haze.

NGC2420isquitebeautifulthroughmy25-cm

reflector at 187×.Someofthebrighterstarsoutlinea

circlewitharingaroundit,remindingmeofSaturn.

This pattern overlies a wealth of very faint to extremely

faint stars. The cluster’s core is about 5′across with a

concentrated centre, but the more sparsely populated

fringe that mantles this core nearly doubles the

cluster’sdiameter.O’Neal9isacute,boxygroupof

ten stars spread over a little more than 3′.Fortunately

forme,NGC2420andO’Neal9arebothdetectable

through the scope’s 9×50 finder. When I last observed

thepair,itwassogustythatthewindkeptpushingmy

scopeawayfromthem.

William Herschel discovered NGC 2420 in 1783

with an 18.7-inch reflector that used a speculum

metalmirror.Heloggeditasa“Clusterofstarsvery

beautiful and close.” Herschel adds that he counted

atleast50starsandsuspectedperhapsdoublethat

number. O’Neal 9 was found in 2005 by California

amateur Mike O’Neal with a 40-cm reflector at

98 ×.It’sincludedasanasterisminthedatabase

oftheDeepSkyHunters,aYahoogroup.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)andOmegaGeminorum.Throughmy130-mm

refractor at 37×,itssunsformastrikingstarburst

array, like an explosion frozen in a moment of time.

Thepatternslightlyoverspillsthecluster’sgiven19′

size.At48×Icount22stars,10thmagnitudeand

fainter, within the 19′boundary.

While NGC 2331 consists of loosely scattered stars,

NGC2266toitswestiswonderfullycrowded.Lookfor

this little gem 1.8°north of Epsilon (ε)Geminorum.

With my 130-mm scope at 23×,itlookslikeafan-

shapedcometwithastaratthehead(south-southwest)

andafainteroneonthesoutheasternside.At102×

anarcofsixstarsbeadsthesoutheasternside,the

brightoneburningyellow.Thewedgeofhazetapering

north-northwest from the arc is densest in the middle

ofitswesternsideanddottedwithabout15veryfaint

stars. A few stars shelter on the arc’s opposite side,

but the entire group covers only 5′.At164×NGC 2266

sports27starsintotal.Thisisacharmingcluster

throughmy25-cmscopeat166×,harboringasplashof

45 diamond-chip stars.

NGC2266bringsourtourtoadelightfulfinish

for visual observers, yet it’s also a grand and colourful

targetforthosewhododeepimagingduringstarry

nights. Why not give it a try?✦

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.

In a somewhat crowded star field, the arc of six colourful

gems on the southeastern side of open cluster NGC 2266

stands out.

NGC 22

NGC 2420

O’Neal 9

PETERSPOKES/ADAM BLOCK/NOAO/AURA / NSF

POSS

-II / STSCI / CALTECH / PALOMAR OBSERVATORY

Targets