54 AUSTRALIAN SKY & TELESCOPE April 2019
adistendeddiffusehalocomposedofstarsanddebris
cannibalised from nearby satellite galaxies. It commands a
swarm of roughly 16,000 globular clusters, one of the largest
knowncollections,andispredictedtoharbourabehemoth
blackholethatweighsinatseveralbillionsolarmasses.
NGC 3308,a12th-magnitudelenticular(S0-type)with
aweakbar,lies6′northwestofNGC3309.Theslightlyoval
halo spans 1′diameterandholdsasmallbrightnucleus.
NGC 3307,just5′westofNGC3309,isamuchtougher
catch. Even through my 45-cm this 14.5-magnitude barred
lenticularwasonlyauniformashenglow,perhaps24′′by 18′′.
Thelargestspiralintheclusteris11.9-magnitudeNGC
3312 ,symmetricallyplacedsoutheastofthecentralpair.In
excellentconditionstherelativelylarge,mistyhalospans
2 ′by 0.7′north-southandenclosesaroundishcorethat
brightenstoastellarpip.A45-cmscopeshouldshowaragged
haloduetolongveinsofdustthattracethewindingspiral
arms,aswellasPGC 31542,asmall14.3-magnitudegalaxy
less than 4′to its east.
NGC 3316,just8′east-southeastofNGC3312,isabarred
lenticularaboutamagnitudefainterthanthepreviousgalaxies(exceptforNGC3307andPGC31542).Its40′′
roundhalobrightensgraduallytoanearlystellarcentre.NGC
3314 forms the southern vertex of an equilateral triangle
with NGC 3312 and NGC 3316. This moderately bright
spindleistiltednorthwestina3:1ratiowithamajoraxisof
1.5′.A13.5-magnitudestarispinnedtoitsnorthwesttip.
TheHubbleSpaceTelescopeimageofNGC3314seemsto
showaspectacularcollisionoftwospirals,butinfactthis
cosmictrompel’oeil(3Deffect)iscreatedbyanearlyperfect
line-of-sightsuperposition.Theface-ongalaxyliesafewtens
of millions of light-years in front of the inclined spiral, and
thereisnoevidenceofarealphysicalinteraction.Visually,
though,evenalargetelescopewillrevealonlythebrighter
background spiral.
Wanttotackleastifferchallenge?PGC 31537,apale
14th-magnitudesmudge,isnearlylostintheglareofthe
5th-magnitudestarHD92036amere3.5′away. With the
starfirmlyplantedoffthenorthedgeofthefield,Iglimpseda
ghostly oval, roughly 25′′inlengthandhalfaswide.
Let’scheckoutsomeclustermembersoutsidethecrowded
centre region. Slide 18′east-southeast of NGC 3314 toHydra I Cluster inhabitants
Object Type Mag(v) Size PA RA Dec.
NGC 3309* E3 11.6 1.9′ × 1.6′ 31° 10 h 36.6m –27° 31′
NGC 3311* E/S0 11.7 2.3′ × 2.1′ 19° 10 h 36.7m –27° 32′
NGC 3308* SAB(s)0 11.9 1.7′ × 1.3′ 32° 10 h 36.4m –27° 26′
NGC 3307 SB(r)0/a pec 14.5 0.9′ × 0.3′ 28° 10 h 36.3m –27° 32′
NGC 3312* SA(s)b pec 11.9 3.3′ × 1.3′ 175° 10 h 37.0m –27° 34′
PGC 31542 SB(s)0 14.3 0.9′ × 0.3′ 167° 10 h 37.3m –27° 34′
NGC 3316* SB(rs)0 12.7 1.3′ × 1.1′ 36° 10 h 37.6m –27° 36′
NGC 3314* Sab 12.8 1.5′ × 0.7′ 143° 10 h 37.2m –27° 41′
PGC 31537 SB0 13.8 1.0′ × 0.4′ 72° 10 h 37.3m –27° 28′
PGC 31638 SB(s)d pec 13.2 1.5′ × 0.7′ 94° 10 h 38.6m –27° 44′
NGC 3336* SAB(rs)c pec 12.2 1.9′ × 1.5′ 123° 10 h 40.3m –27° 47′
NGC 3285* SB(s)a pec 12.0 2.6′ × 1.3′ 108° 10 h 33.6m –27° 27′
NGC 3285B SAB(r)b 13.1 1.5′ × 1.1′ 43° 10 h 34.6m –27° 39′
NGC 3315* E /S0 13.4 1.1′ × 1.0′ 80° 10 h 37.3m –27° 11′
NGC 3305* E0 12.8 1.1′ × 1.1′ – 10 h 36.2m –27° 10′
IC 2597* E4 11.8 1.5′ × 1.2′ 4° 10 h 37.8m –27° 05′
PGC 31588 Sc 14.0 0.9′ × 0.8′ 97° 10 h 37.8m –27° 07′
NGC 3313* SB(r)b 11.4 3.9′ × 3.2′ 55° 10 h 37.4m –25° 19′
NGC 3393* (R’)SB(rs)a 12.2 1.8′ × 1.5′ 48° 10 h 48.4m –25° 10′
Angular sizes and separations are from recent catalogues. Visually, an object’s size is often smaller than the catalogued value and varies according to the aperture
and magnification of the viewing instrument. Right ascension and declination are for equinox 2000.0. The asterisk following the galaxy name denotes primary
cluster member.HYDRA I CLUSTER