Australian Sky & Telescope - 04.2019

http://www.skyandtelescope.com.au 53

at the beginning of April and an hour

earlier around the new Moon at mid-

month.

The core of the Hydra I Cluster

forms a wide isosceles triangle with

4th-magnitude Alpha (α) Antliae and

5th-magnitude 44 Hya. The cluster is

slightly under 4° from either star, lying

just to the east of a line connecting the

two stars. The main drag of the cluster’s

core is easy to follow as it forms a 20′

chainpassingbetween4.9-magnitude

HD 92036 and 6.7-magnitude HD

91964.You’llfindhalfadozenbrighter

NGCgalaxies,buttheglarefromthese

stars can be an annoyance, so use

medium or high power and isolate them

outside the eyepiece field whenever

possible.Mydescriptionsarebasedon

observationsthrougha33-cmreflector

using 166×and 214×from dark sites.

STHE CLUSTER IN THE COILSTheHydraIGalaxyCluster,consistingofmorethan100members,liessome165millionlight-yearsawayina

rather isolated corner of space.

XTHE COLOSSUS IN THE CLUSTER NGC

3311, in the centre of this image, is by far

the largest galaxy in the Hydra I cluster and

presumably hosts a supermassive black

hole. What makes this galaxy even more

remarkable, though, is the swarm of some

16,000 globular clusters in its halo, the largest

collection of its kind known to date. To the

right lies cluster member NGC 3309, another

large elliptical galaxy, although less massive.

The dark shadow at the bottom of the image is

the spectrograph’s guide probe.

NGC 3315

PGC 31537

NGC 3312

PGC 31542

NG

NGC 3309

NGC 3307

NGC 3308

NGC 3285B

NGC 3316

NGC 3314

PGC 31638

NGC 3305

NGC 3311: GEMINI OBSERVATORY / AURA; HYDRA I CLUSTER: J. PÖPSEL / S. BINNEWIES / CAPELLA OBSERVATORY

Let’s start with NGC 3309 and NGC

3311 , which form an impressive pair at

the heart of the cluster. NGC 3309, an

11.6-magnitude elliptical, is strongly

condensed with a conspicuous 40′′ core

encased in a slightly elongated 1.2′

halo leaning northeast. NGC 3311,

just 1.7′ east-southeast, is similar in

size and magnitude but more broadly

concentrated with no distinct nucleus.

Using averted vision, its tenuous outer

envelope grows to nearly 2′ in diameter

with a 13.5-magnitude star sandwiched

between the halos of the two elliptical

galaxies.

NGC 3311 is a colossal cD-type

(central dominant) galaxy with