62 M63
Among the heavens’ most beautifully haphazard galaxies is M63, the
Sunflower Galaxy. This massive, curdled spiral sports only two arms, but
their flocculate (feathery or disjointed) nature makes them hard to define.
M63 is nicknamed the Sunflower Galaxy because of its resemblance
to the dense, seedy head of that towering plant, which is ringed by an
abundance of bright, overlapping petals. In images, it’s the vast infiltra-
tion of dust that largely allows the eye to trace out the spiral’s structure,
which shows up more clearly in infrared images.
M63 was a Pierre Méchain discovery. A contemporary of CharlesNamed for the constellation in which it
appears, the Triangulum Galaxy (M33) is
the third largest member of the Milky Way’s
Local Group of galaxies. Only the Andromeda
Galaxy (see #100) and the Milky Way are
bigger.
M33 lies about 2.7 million light-years away.
And like its hefty galactic neighbors, it is a
spiral galaxy. However, unlike Andromeda and
the Milky Way, both of which are classified as
barred spirals, the Triangulum Galaxy does
not exhibit a central bar-shaped structure. Its
spiral arms instead extend directly from its
core. The arms of Triangulum are also less
tightly wound than those of Andromeda and
the Milky Way, stretching out across some
50,000 light-years, or about half the diameter
of our own galaxy. M33 holds roughly half as
many stars as the Milky Way.
Unlike Andromeda, which we see nearly
edge-on, Triangulum presents itself almost
face-on. This affords astronomers a great
opportunity to study a nearby spiral's structure.
Many ionized HII regions are scattered
across Triangulum’s disk. These pockets ofglowing hydrogen gas come to life in photos
taken through large ground-based telescopes
and the Hubble Space Telescope. The largest
HII region in M33 is separately cataloged as
NGC 604. Astronomers estimate this massive
star-forming borough stretches across more
than 1,500 light-years, making it at least some
40 times larger than our own Orion Nebula.
While observers have closely scrutinized
the Triangulum Galaxy since its discovery, it’s
ironic that it often eludes amateurs trying to
spot it for the first time. Even though it is rated
at 6th magnitude, M33 has a very low surface
brightness due to its large apparent diameter
in our sky. That causes it to blend seamlessly
into the background. Many searching for M33
pass right over it without even noticing.
It’s easier to spot the galaxy’s glow through
the wider fields of binoculars and finder
scopes. If you are targeting it through a
telescope, however, use averted vision and
your lowest-power eyepiece for the best view.
Then, once you find the galaxy, try tracking
down NGC 604. It will look like a small glow-
ing patch just northeast of M33’s core. — P. H.60 M94
Nestled between the two brightest stars in
Canes Venatici lies M94, a beautiful spiral
galaxy 16 million light-years distant.
Pierre Méchain discovered M94 on March 22,
1781, and communicated its position to Charles
Messier. Messier saw a “nebula” with a bright
center surrounded by a condensed halo. But
William Parsons, Earl of Rosse, found the
“nebula” broken into patches — suggesting that
the “object will probably turn out to be a spiral”
— with “much faint outlying nebulosity.”
Lord Rosse’s words were prophetic. M94 is
a nearly face-on early spiral galaxy that only
10 million years ago may have experienced a
violent explosion, which disgorged millions of
solar masses of material. The galaxy possesses
a curious multi-layered appearance, including a
central “spiral” about 30,000 light-years across
with a broad, faint outer ring some 40,000 light-
years farther out. This outer “ring” is actually
two giant, star-forming spiral arms extending
from the galaxy’s inner disk.
M94’s tightly wrapped inner arms appear
yellowed with age and show little evidence of
recent star formation. In contrast, the galaxy’s
nuclear region reveals an unusual starburst
ring and two point sources, both bright in
ultraviolet light. This suggests that two objects
— compact star clusters or supermassive black
holes — are in the final stages of merging.
Under moderate to high powers through
a telescope, the 8th-magnitude galaxy’s disk
becomes a hypnotic sight: Its bright core with
a central pip, surrounded by a soft gel-like
elliptical disk, looks like an eye staring back at
you. The galaxy’s dim outer rings can be spied
through 4-inch telescopes under dark skies as
a soft halo of light. Larger apertures will resolve
its ringlike structure more clearly. — S.J.O.
DAN CROWSONADAM PHILLIPS61 The Triangulum Galaxy