Sky and Telescope - April 2018 - 34

Hydra I Cluster

halo due to long veins of dust that trace the winding spiral
arms, as well as PGC 31542, a small 14.3-magnitude galaxy
less than 4′ to its east.
NGC 3316, just 8′ east-southeast of NGC 3312, is a barred
lenticular about a magnitude fainter than the previous galaxies (except for NGC 3307 and PGC 31542). Its 40″ round
halo brightens gradually to a nearly stellar center. NGC 3314
forms the southern vertex of an equilateral triangle with
NGC 3312 and NGC 3316. This moderately bright spindle
is tilted northwest in a 3:1 ratio with a major axis of 1.5′. A
13.5-magnitude star is pinned to its northwest tip.
The Hubble Space Telescope image of NGC 3314 seems to
show a spectacular collision of two spirals, but in fact this
cosmic trompe l'oeil is created by a nearly perfect line-ofsight superposition. The face-on galaxy lies a few tens of
millions of light-years in front of the inclined spiral, and
there is no evidence of a real physical interaction. Visually,
though, even a large telescope will reveal only the brighter
background spiral.
Want to tackle a stiffer challenge? PGC 31537, a pale
14th-magnitude smudge, is nearly lost in the glare of the

5th-magnitude star HD 92036 a mere 3.5′ away. With the
star ﬁrmly planted off the north edge of the ﬁeld, I glimpsed a
ghostly oval, roughly 25″ in length and half as wide.
Let's check out some cluster members outside the crowded
downtown region. Slide 18′ east-southeast of NGC 3314 to
13th-magnitude PGC 31638. Images show a disrupted spiral,
but visually it was just an amorphous patch about 40″ across
with a 13.5-magnitude star barely off the southwest edge.
Continue another eyepiece ﬁeld in the same direction and
you'll arrive at NGC 3336 in the eastern outskirts of the
cluster. This 12th-magnitude spiral showed a diffuse 1′ halo
with a weakly brighter central hub.
NGC 3285, another 12th-magnitude spiral, resides in the
cluster's western suburbs. Look for it 37′ due west of NGC
3308 and 7′ southwest of 7.4-magnitude HD 91551. A moderately faint 60″ × 45″ halo is tilted west-northwest and rises
broadly to a quasi-stellar nucleus. NGC 3285B, a dimmer
barred spiral 18′ to its southeast, only revealed a slightly outof-round 1′ diaphanous halo.
NGC 3315 is found 13′ north of HD 92036 and close
to the east of a 10th-magnitude star. This small fuzz-ball

Hydra I Cluster Components
Object
NGC 3309*
NGC 3311*
NGC 3308*
NGC 3307

Type

Mag(v)

Size

PA

RA

Dec.

E3

11.6

1.9′ × 1.6′

31°

10h 36.6m

-27° 31′

11.7

2.3′ × 2.1′

19°

10h

36.7m

-27° 32′

11.9

1.7′ × 1.3′

32°

10h

36.4m

-27° 26′

14.5

0.9′ × 0.3′

28°

10h

36.3m

-27° 32′

37.0m

-27° 34′

E/S0
SAB(s)0
SB(r)0/a pec

NGC 3312*

SA(s)b pec

11.9

3.3′ × 1.3′

175°

10h

PGC 31542

SB(s)0

14.3

0.9′ × 0.3′

167°

10h 37.3m

-27° 34′

12.7

1.3′ × 1.1′

36°

10h

37.6m

-27° 36′

12.8

1.5′ × 0.7′

143°

10h

37.2m

-27° 41′

13.8

1.0′ × 0.4′

72°

10h

37.3m

-27° 28′

38.6m

-27° 44′

NGC 3316*
NGC 3314*
PGC 31537

SB(rs)0
Sab
SB0

PGC 31638

SB(s)d pec

13.2

1.5′ × 0.7′

94°

10h

NGC 3336*

SAB(rs)c pec

12.2

1.9′ × 1.5′

123°

10h 40.3m

-27° 47′

12.0

2.6′ × 1.3′

108°

10h

33.6m

-27° 27′

13.1

1.5′ × 1.1′

43°

10h

34.6m

-27° 39′

13.4

1.1′ × 1.0′

80°

10h

37.3m

-27° 11′

10h

36.2m

-27° 10′

NGC 3285*
NGC 3285B
NGC 3315*

SB(s)a pec
SAB(r)b
E/S0

NGC 3305*

E0

12.8

1.1′ × 1.1′

-

IC 2597*

E4

11.8

1.5′ × 1.2′

4°

10h 37.8m

-27° 05′

PGC 31588

Sc

14.0

0.9′ × 0.8′

97°

10h 37.8m

-27° 07′

11.4

3.9′ × 3.2′

55°

10h

37.4m

-25° 19′

12.2

1.8′ × 1.5′

48°

10h

48.4m

-25° 10′

NGC 3313*
NGC 3393*

SB(r)b
(R')SB(rs)a

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 magnification of the viewing instrument. Right ascension and declination are for equinox 2000.0. The asterisk following the galaxy name denotes primary
cluster member.

34

A PR I L 2 018 * SK Y & TELESCOPE
Sky and Telescope - April 2018

Table of Contents for the Digital Edition of Sky and Telescope - April 2018
