Sky and Telescope - May 2015 - 60

OBSERVING

Going Deep

POSS-II / STSCI / CALTECH / PALOMAR OBSERVATORY

NGC 5577

NGC 5576
NGC 5574

KTG 55. William Herschel noted that NGC 5574 was "pretty
bright, pretty large, extended." He described the more prominent NGC 5576 as "considerably bright, round, pretty large."

in April 1786, placing NGC 5566 in his Class I of Bright
Nebulae. Today you'll ﬁnd NGC 5566 included in the
Astronomical League's Herschel 400 Observing Program.
NGC 5566 is easily visible in a 6-inch scope as a 2′
oval with a strong core. Through my 24-inch reﬂector
at 200×, the low surface brightness outer halo is very
diﬀ use, but expands beyond 4′ in length with averted
vision, sloping from northeast to southwest in a 3:1 ratio.
A strongly condensed oval core harbors an intense, elongated nucleus or bar that angles nearly north and south.
Two 12th- and 14th-magnitude stars bracket the core to
the east and west. Images reveal NGC 5566 as a doublebarred spiral, with an inner nuclear ring or spiral.
NGC 5560, 5′ to the northwest, is a fairly bright
slender streak with a relatively large, elongated core. A

14th-magnitude star perches just north of the bright center. The arms extend 2.0′ long and are one-third as wide,
tapering towards the tips, with the major axis perpendicular to NGC 5566. NGC 5560's warped arms are likely
due to the gravitational interaction with NGC 5566.
NGC 5569 is an anemic, low surface brightness
spiral oﬀ the northeast end of NGC 5566; it may require
a 12-inch or larger aperture to get a good look at this one.
Through my 18-inch scope at 220×, the spiral galaxy is a
tenuous, very diﬀuse glow, perhaps 1′ in diameter, with
only a weakly enhanced core. George Johnstone Stoney,
the observing assistant on William Parsons's (3rd Earl of
Rosse) mammoth 72-inch reﬂector, discovered NGC 5569
in April 1849 while examining the brighter pair nearby.
Next stop on our tour is KTG 55, a mere 40′ southsoutheast of KTG 54. These neighbors have similar
redshifts, implying a common distance of 70-80 million
light-years. Together they form a chummy sextet in the
relatively local universe.
NGC 5576, the brightest of the trio, is also in Herschel's Class I and on the 400 Program. Through a 6-inch
at 100×, NGC 5576 is a moderately faint oval, 1.5′ long and
two-thirds as wide, with a slightly brighter core. With my
24-inch, the halo swells to 2.0′ × 1.6′ and fades imperceptibly into the background. A prominent core that brightens
to a stellar nucleus dominates the galaxy. A 13th-magnitude star brushes against the halo on the northwest side.
+20°
Star magnitudes

KTG 55

Arcturus

BOOTES
+5°

14h 28m

IC 4424
UGC 9258

14h 26m

14h 24m

14h 22m

14h 20m

2
3
4
5
6

+10°

5619

KTG 57
KTG 57
KTG 54

VIRGO

KTG 55

VIRGO

0°

5569

+4°

Star magnitudes

KTG 54
6
7
8
9
10

5566

-10°

5577
5576

KTG 55
5574

5560

May 2015 sky & telescope

LIBRA
Spica

15h 00m

14h 30m

14h 00m

13h 30m

Sky and Telescope - May 2015

Table of Contents for the Digital Edition of Sky and Telescope - May 2015