76 M65 and M66
A twin treat, M65 (top right) and M66 (bottom right) in Leo are arguably the most dynamic
galaxy pair in the northern night sky, next to M81 and M82 in Ursa Major. Under a dark sky,
binoculars will show them as two roughly magnitude 9 glows 20' apart. Together with the dim-
mer edge-on spiral galaxy NGC 3628 (35' to the northeast), they form the famed Leo Triplet of
galaxies. All lie about 35 million light-years distant, in the Leo Spur — a little gathering of galax-
ies between the Local Group and Virgo Cluster. We see all three galaxies presented at different
viewing angles, allowing us to inspect their spiral structure from different perspectives.
Charles Messier discovered both M65 and M66 in 1780, midway between Theta (θ) and
Iota (ι) Leonis, noting they were “in the same field of view.”
In 1848, William Parsons, Earl of Rosse, resolved M65 into a “spiral or annular arrangement.”
He later noticed dark lanes on either side of the nucleus. Indeed, the inclination of M65 is
nearly optimal to show the galaxy’s dust silhouette, which traces a well-defined spiral pattern
with two main arms. At its center lies a diffuse nucleus and bar embedded in a tiny central
bulge. Through a moderate-sized telescope at 70x, its spiral structure requires attention —
though the pattern appears coiled north of the nucleus, the southern disk region requires larger
apertures to resolve.
M66, on the other hand, is a Milky Way-sized barred galaxy that sports prodigious dust, a
displaced core, and grand spiral arms. One of these arms is “hooked,” thanks to distortions suf-
fered in a gravitational war with NGC 3628. A fantastic 400,000-light-year-long tidal tail has also
been detected between these two galaxies, the result of an encounter a billion years ago.
Through a telescope at moderate magnifications, M65 appears oval-shaped and quite large
compared to M66, which is a much more difficult object to study. M66’s bright nuclear region
stands out the most, with extensions that form the “trunk” of its S-shaped spiral structure,
which large telescopes will show as soft strips of dappled light. — S.J.O.
78 M 74
A phantom among the bright galaxies, M74 is one of
the closest and largest face-on spirals in the sky — yet
it is difficult to observe, especially from light-polluted
areas. Under a dark sky, the galaxy is a wonder. Just
32 million light-years away in Pisces, this grand-
design spiral of 100 billion stars sports perfectly sym-
metrical spiral arms unwinding from a blazing core.
The galaxy’s entire disk, tilted only 5° away from
face-on, has undergone active star formation within
the past 500 million years. By contrast, its inner
regions have a dearth of young stellar specimens —
an example of how galaxies regulate star formation
over time. Thick dust lanes also join the arms out to
a quarter of a revolution before they begin to thin.
Pierre Méchain discovered M74 in 1780 and wrote
to Charles Messier: “It is quite broad, very dim, and
extremely difficult to observe.” Indeed, to this day, M74
has proven to be the most troublesome and elusive
object in Messier’s catalog. The problem is that the
galaxy’s large apparent size (11') and low surface
brightness (14.4 magnitudes per square arcsecond),
requires a very dark sky to be seen. If the skies are
dark enough, however, skilled observers can pick out
the galaxy using humble binoculars.
M74 lies about 1¼° east-northeast of Eta (η)77 The Coalsack
Nebula
The Coalsack Nebula is the most famous naked-eye
dark nebula in the entire sky. Located in the Southern
Hemisphere next to the Southern Cross (see #3), the
shadowy nebulosity looks like a large void (5° by 7°)
in the bright, flowing stream of the Milky Way. That’s
more than large enough to fill most binocular fields.
While the majority of observers see the Coalsack as
a uniform black patch, with careful scrutiny, some can
detect intricate filamentary details within. For viewers
to perceive these subtleties, the night must be free of
both moonlight and earthly interference like light pol-
lution and atmospheric dust.
The Coalsack was well known to early cultures.
Inca legends tell how the creation god Ataguchu
once became so enraged that he kicked the Milky
Way, causing a portion of it to fly off and creating the
Small Magellanic Cloud. The hole left behind was the
Coalsack. Australian Aboriginal lore, meanwhile, refers
to it as the head of an emu, even drawing a starless
constellation of the lanky bird’s body that follows the
form of the Milky Way’s stream northward.
However, we should refer to the Coalsack as the
Dustsack, because that’s what it is: a gargantuan cloud
of interstellar dust some 600 light-years away, making
it the nearest substantial dark nebula to our solar
system. Each grain of cosmic dust within is coated
with an outer layer of water ice and simple organic
molecules such as frozen carbon monoxide. The dust
is so dense in regions that it blocks most of the visible
light from stars behind the cloud. The bit of starlight
that does seep through takes on a reddish tint. This
effect, called interstellar reddening, occurs as the dust
particles preferentially absorb and scatter blue light.
But like planetary nebulae, the Coalsack won’t last
very long in cosmic terms. Fast-forward millions of
years and this dusty void will have transformed into a
display of newly sparkling stellar diamonds. — P. H.JARED BOWENSCHIRAG UPRETI