Just as springtime is galaxy time, so early summer is
time for observing globular clusters. Of the 15
Messier objects between RA 15 and RA 18, 12 are globular
clusters. These include clusters like M5 and M13 which
rank high among the showpieces of the northern sky and
also modest clusters like M107 which show well only in
large telescopes, especially under light pollution.
The concentration of globular clusters is no accident.
Throughout the early summer, the Milky Way can be seen
slowly rising almost parallel to the eastern horizon.
Globular clusters are associated with the Milky Way,
but they are not tightly bound to the galactic plane,
like most nebulae and open clusters. The globular
clusters of early summer are harbingers of middle and
late summer, when the most magnificent section of
the Milky Way lies directly overhead, and stretching
down to the southern horizon.
A similar collection of globular clusters tags along
behind the Milky Way in autumn. Globular clusters are
heavily concentrated towards the galactic core, which
lies in Sagittarius in the summer Milky Way. That is
why so few globular clusters are visible in the winter,
when we look out towards the edge of the galaxy.
For observers in the southern hemisphere, spring and
early summer are also fine times for viewing nebulae
and open clusters in the Milky Way proper, but this
part of the Milky Way, through Centaurus, Crux, and
Carina, is forever hidden from observers north of the
Tropic of Cancer. Only around RA 17:30 in Scorpius
does the galactic plane climb far enough north to be
visible from Messier's latitude. That accounts for
the appearance of the two magnficent open clusters
M6 and M7 at the very end of this section. M7 is
the most southerly of all the Messier objects, but
it is so bright that it shines even through very
heavy light pollution low in the sky.
Here are the Messier objects from RA 15 through RA 18,
excluding M23, at RA 17:56.8, which fits naturally with
the late-summer objects.
For a key to this table, see
Key to the Tables.
With the exception of the two wonderful globular clusters
in Hercules, the Messier objects from RA 15 to RA 18 are
concentrated fairly far south, and so are best observed
for the brief time when they are at their highest in the
south. This is particularly true for the objects in
Scorpius, a wonderful constellation which is never really
well placed for observers much north of latitude 30N.
That is a pity; Scorpius rivals Orion both in its naked-eye
appearance and in the deep-sky objects that it contains.
Many of the late-spring galaxies, notably the ones in Ursa
Major and Canes Venatici, remain well-placed well into the
summer for observers in the North Temperate Zone. I often
view them in the summer for a change of pace, but mostly
I am drawn to the finest galaxy of all -- our own Milky Way.
You can see more detail in the Milky Way with your unaided
eyes than you can see in any other galaxy through the
finest telescope. Unfortunately, the finest objects of
the summer Milky Way are quite far south, and are
tantalizingly low in early summer evenings as seen
from my latitude.
M5 is my personal favorite among all the globular clusters
in the Messier list. M13 is better known, and undeniably
magnificent, but I find M5 more shapely. M22 and M4 are
easier to resolve than either M5 or M13, but they are too
far south for optimal viewing from my latitude of 42N,
especially under serious light pollution.
M5 is extremely easy to locate under dark skies, lying as
it does just 22' NW of 5 Serpentis. But at mag 5.1,
5 Serpentis is likely to be visible only in the best
suburban skies. It can also be hard to distinguish
5 Serpentis from the numerous other stars in the vicinity,
notably mag 5.2 10 Serpentis 2 degrees to the E and mag 5.4
6 Serpentis 1 degree to the SSE.
Under good urban skies and most suburban skies, with
limiting magnitude of 4.2 or better, I like to locate
5 Ser and M5 starting with the head of Serpens, a
striking nearly equilateral triangle of stars. Proceed
from Kappa Ser, the northmost and faintest star of the
triangle, through Delta Ser, and continue on slightly
farther, and bending slightly south, and there is M5.
If the head of Serpens is not readily visible, then M5
is an 8-degree hop from mag 2.6 Alpha Serpentis.
M5 is readily visible under urban skies in my 7x35
binoculars as a small, bright, fuzz ball. It looks
quite similar in my 70mm scope, with a small, very
bright core around 2' inside a fairly bright 5' halo.
M5 really comes into its own in larger scopes. Even under
urban skies, my 178mm scope shows several stars clearly
with averted vision, while many more appear intermittently.
M5 is magnificent in my 178mm scope under suburban skies,
again showing a very bright 2' core inside a 5' halo, but
also showing a much fainter halo extending nearly to a
15' diameter, studded with a huge number of stars that
appear intermittently with averted vision and about two
dozen stars that appear consistently with direct or
M5 appears better still in even larger scopes and/or under
darker skies. The stars in the halo appear to lie upon
well-defined arms, slightly curved, with the brightest
and longest arm stretching nearly N.
M13 and M92
M13, the Great Cluster in Hercules, is the most famous
globular cluster north of the Celestial Equator. As I have
said, I do not consider it as attractive as M5, but it is
indisputably magnificent. M92, the other cluster in
Hercules, is overshadowed by its giant companion, but
it is a wonderful cluster in its own right, almost as
easy to resolve as M13, although much smaller. Both
clusters have the virtue (for observers in the North
Temperate Zone) of lying quite far north in the sky,
so that they remain well-placed in the evening sky from
early spring throughout the summer.
M13 and M92 are both located off the Keystone of Hercules.
This is a lovely asterism, but a little hard to recognize
even under dark skies, and much harder under significant
light pollution. Epsilon Herculis, the faintest of the
four stars of the Keystone at mag 3.9, may well be
invisible under poor skies, and none of the stars is
genuinely bright. The Keystone is also large and loose,
making it even harder to identify.
One easy way to find the Keystone is to start with the
unmistakable blue-white star Vega; the Keystone lies
about 2/5 of the way from there to Arcturus. Somewhat
farther along the same line is the much tighter and
finer constellation of Corona Borealis. When looking
for the Keystone, my eye is often caught by the head
of Draco, an asterism with a very similar shape, but
much brighter and tighter. Vega, the head of Draco,
and the Keystone form a nearly equilateral triangle.
Once the Keystone is found, M13 is very easy to locate,
1/3 of the way from Eta to Zeta Herculis, on the W edge
of the Keystone. M92 is a good deal harder to locate.
It forms a slightly lopsided triangle with Pi and Eta
Herculis, being about 1.5 degrees too far E to form an
equilateral triangle. It also lies about 2/5 of the
way from Iota Herculis to Eta. And it is a modest
6-degree star-hop from Pi.
Like M5, M13 is readily visible through even the smallest
instrument even under very poor skies. In fact, M13 is
visible to the naked eye as a small, faintish but fairly
concentrated fuzzy patch under reasonably dark skies.
M13 lies halfway between a mag 6.9 star and a mag 7.3
star, but slightly NW of the line connecting those stars.
In my 70mm scope, M13 shows a very bright 2' core surrounded
by a halo which ranges in size from about 3.5' under urban skies
to about 7' under suburban skies. The halo appears distinctly
grainy at high power under good suburban skies, but it does not
really resolve into individual stars.
M13 shows the same 2' core and 7' halo in my 178mm scope, much
brighter of course, and it also resolves numerous individual
stars with at high power, especially with averted vision, and
especially in the halo. I can pin down about 8 stars under
urban skies and about 16 stars under suburban skies, and
several times that number appear intermittently with averted
vision in both cases. Several of the faint stars appear well
outside the halo, to a diameter of 10' - 15', and although it
is hard to tell which ones properly belong to the cluster, the
borderline faint stars are clearly richer in the vicinity of
the cluster than in the background.
M92 is also readily visible in my 7x35 binoculars under urban
skies, but it is so small that it is a little hard to tell
that it is non-stellar. A chain of 3 stars lies quite closeby
to the NNE, and M92 is distinctly brighter than the northmost
and brightest of those 3 stars, which is mag 8.6.
In my 70mm scope, M92 shows a very compact and very bright core
about 1' across, inside a faint halo about 2' across under urban
skies, and slightly larger under suburban skies.
The core appears even brighter and smaller in my 178mm scope,
and a very faint outer halo about 4' - 5' in diameter appears
around the brighter inner halo, especially under good suburban
skies or darker. Numerous stars appear intermittently with
averted vision in the inner halo. I can pin down about 5 under
urban skies and maybe 10 under suburban skies.
M4 and M80
M4 is one of the closest globular clusters to Earth,
at a distance of roughly 7,000 light years; therefore,
it appears unusually large, and its stars appear
unusually bright to us. It is also rather sparse
as globular clusters go, giving it a fairly modest
surface brightness. The brightness of the individual
stars, combined with the fact that they are fairly
widely separated, makes this probably the easiest of
all the Messier globular clusters to resolve into
individual stars in small instruments -- at latitudes
where it rises reasonably high in the sky.
At my own latitude of 42N, M4 never gets very far above
the horizon, and in the city and the suburbs, it is always
buried in the low-lying haze of light pollution, which
greatly detracts from its appearance. Even so, it is
a wonderful sight in my 178mm scope.
Just as M92 will forever be known as "the other globular
cluster in Hercules", so M80 is the other globular cluster
in Scorpius. Although M4 and M80 appear close together in
the sky, M80 is actually about four times farther from
Earth, at around 27,000 light years. Morphologically,
M80 is at the opposite end of the spectrum from M4; where
M4 is large and diffuse, M80 is highly concentrated.
M4 is extremely easy to locate, being just 1.3 degrees W
of dazzling, deep-red Antares, one of the most prominent
stars in the sky. Antares means "rival of Ares", Ares
being another name for Mars, the Red Planet. Antares
lies very close to the ecliptic, the path that the Sun
and the planets follow through the sky, so Mars and
Antares can sometimes be seen right next to each other,
rivalling each other in redness and in brilliance.
M4 would be readily visible under dark skies if not for
its proximity to Antares, which tends to overpower it.
In my 7x35 binoculars, it is an easy target under suburban
skies or darker, showing as a large but faint patch of
light. Under urban skies, at my latitude of 42N, M4's
low surface brightness makes it invisible in small
In my 70mm scope, at latitude 42N, M4 is barely visible
as an extended patch barely brighter than the background,
showing best at 40X. The view is far better in the
suburbs, where M4 shows as a faint but definite 6' circle,
with two stars faintly visible on the W edge. Under dark
skies, my 70mm scope resolves perhaps a dozen stars in
and around a 10' halo.
My first view of M4 through my 178mm scope in the city was
unforgettable. At low power, the cluster was barely visible.
At around 40X, a large, ragged, ethereal cloud began to take
shape. When I raised the power to 120X, numerous stars
suddenly swam into view out of a barely-visible cloud,
with dozens more appearing at the edge of my field, and
disappearing when I tried to catch them with direct vision.
The overall effect was utterly magical.
In the 178mm scope under suburban skies, I can pin down about
two dozen stars in M4, with numerous others at the edge of
averted vision. A striking feature of M4 both visually and
in photographs is the string of bright stars running in a
straight north-south line, slightly W of the cluster's
center. Even when the individual stars cannot be resolved,
the bright central line is quite prominent.
M80 can be a little tricky to locate, especially because
its small size and high surface brightness make it appear
nearly stellar at low power. One way to locate it is by
aiming halfway between Antares and Beta Scorpii (Graffias),
the topmost star of the prominent arc lying W of Antares.
M80 also forms a nearly perfect parallelogram with Antares,
Sigma Scorpii, and Rho Scorpii, but at mag 5.1, Rho is
unlikely to be visible even in good suburban skies in the
North Temperate Zone. Perhaps you can imagine where it lies.
M80 is also a modest 3-degree starhop from Sigma.
In the eyepiece, M80 appears like a fuzzy star in the middle
of a zigzag line of three other stars of similar brightness
about 20' long. Its high surface brightness makes it readily
visile under urban skies both in my 70mm scope and in my 178mm
scope, but nothing can be seen except for the tiny, nearly
Under suburban skies, at high power, I can see a subtle halo
around the miniscule core, about 1' across in my 70mm scope
and 1.5' in my 178mm scope. There is no hint of resolution
even in the larger scope.
M19 and M62
M19 and M62 are a pair of globular clusters, rather
similar in size and brightness, that lie in the SW
corner of Ohpiuchus, just E of the body of Scorpius.
They are both fine and interesting objects in a large
scope under a dark sky, but they are too far south to
show well through light pollution at my latitude of 42N.
To find these objects, start with Antares, then locate
Theta Ophiuchi 12 degrees to the E, and Epsilon Scorpii
9 degrees SSE of Antares. Both of those other stars
may pose problems. Theta Oph is only mag 3.3, which would
be quite bright high in the sky but may be hard to see
if it lies close to the horizon. Epsilon Sco is amply
bright at mag 2.3, but at my latitude, it is only visible
from sites with an unusually low southern horizon.
M19 lies just S of a point 2/5 of the way from Theta Oph
to Antares, and it is a modest hop from either star if that
method fails. M62 lies just NW of a point 2/5 of the way
from Epsilon Sco to Theta Oph, and is a modest hop from
Epsilon. Once either of the two clusters is found, it is
a modest star-hop to the other.
M62 is the brighter of the two clusters, and that is even
truer in appearance than the raw magnitudes would suggest,
probably because M62 is much more concentrated towards
the center. M62 is easy to see under urban and suburban
skies both in my 70mm scope and in my 178mm scope, and it
appears strikingly similar regardless of aperture,
magnification, and skyglow, as a concentrated 1.5' circle.
M19 is rather hard to see in my 70mm scope under urban
skies, showing as a 3' circle with averted vision at 40X
to 60X. It is much easier in my 178mm scope, but still
is only borderline with direct vision at 120X.
Under suburban skies, M19 appears reasonably bright both
in my 70mm scope and in my 178mm scope. Again, it appears
about 3' across, but in my 178mm scope, it is unmistakeably
elliptical -- a very exotic feature in a globular cluster --
being slightly elongated north-south.
M9 is easy to locate, but it is one of the faintest and
least interesting of Messier's globular clusters.
To locate M9, start at Eta Ophiuchi, which at mag 2.5 should
be readily visible in all but the worst skies. M9 lies 3.5
degrees to the SSE, more or less continuing the line of stars
marking the W edge of Ophiuchus.
M9 is barely perceptible with averted vision in my 70mm scope
under urban skies, showing as a 1' smudge with a pointlike
center. It is much easier in that scope under suburban skies,
showing with direct vision as a 2' circle with a brighter core.
In my 178mm scope, M9 shows about 1.5' across under urban skies
and about 2' under suburban skies. In both cases, it is
moderately faint, moderately concentrated, and not very hard
M107 is even easier to locate than M9, and even fainter.
M107 lies 3 degrees SSW of mag 2.6 Zeta Ophiuchi, in the
direction of Graffias (Beta Scorpii, the northmost star
in the arc W of Antares).
Under urban skies, M107 is invisible in my 70mm scope and
very difficult in my 178mm scope, showing as a 1.5' circle
with averted vision.
M107 is much easier to see under suburban skies, showing
fairly easily with averted vision in my 70mm scope and with
direct vision in my 178mm scope. In the smaller scope, it
shows as a featureless 2' blob, rather hard to pin down.
In the larger scope, it is a vague circle about 3' across
with a brighter 1' core.
M10 and M12
M10 and M12 are a pleasant change of pace from the faint,
nearly featureless globular clusters described above.
They are among the finest of all globular clusters --
bright, bold, and easy to resolve. M10 and M12 are
nearly twins, but M10 is slightly brighter, closer,
and easier to resolve.
The clusters are separated by only 3 degrees, making
it quite easy to star-hop from one to the other, but
the pair is a bit of a nuisance to locate unless the
sky is dark enough to see the mag 4.8 star 30 Ophiuchi,
which lies just 1 degree E of M10.
The key to locating the general region of the sky is
the wonderful star pair of Yed Prior and Yed Posterior,
Delta and Epsilon Ophiuchi, respectively. They are
not terribly bright, at mag 2.7 and 3.2, but their
proximity makes them very striking; the only other
place in the sky where two stars so bright appear so
close together is in Orion's belt. Both stars are
also visibly reddish, especially Yed Prior.
Once the Yeds are located, Zeta Ophiuchi (the jumping-
off star for M107) should be trivial. If you can also
see Lambda Ophiuchi to the N, at mag 4.1, then you may
be able to locate M10 by the fact that it forms a
parallelogram with Lambda, Zeta, and Delta (Yed Prior).
Alternatively, M12 is a moderate 6-degree hop from
Lamda, or you can hop to either cluster from any of
the other stars if Lambda is invisible or obscure.
Both clusters are fairly easy to see in my 7x35 binoculars
under urban or suburban skies, but they are small enough so
that it is possible to confuse them with stars.
Neither cluster shows much detail in my 70mm scope. Somewhat
surprisingly, M12 is significantly less prominent than M10 in
that scope both under urban and suburban skies, but neither
cluster could possibly be called difficult to see. M10
appears more concentrated, roughly 4' across with a 2' core
in the suburbs, and a fairly featureless 3.5' circle in
the city. M12 is a featureless faintish smudge in the 70mm
scope from the city and a large, slightly dull blob in the
Both clusters show far better in the 178mm scope, which
is big enough to resolve quite a few stars in each cluster
even in the city, and many more in the suburbs. Both
clusters do best at high power -- at least 120X -- to bring
out the individual stars. I can pin down 7 stars in M12
using averted vision in the city and 10 in the suburbs,
with many more popping out intermittently. M10 is even
better, showing 8 stars with averted vision in the city,
and giving an overall impression of stardust in the
background. I can make out perhaps two dozen stars in
M10 in the suburbs, but some are hard to pin down.
M14, the easternmost globular cluster in Ophiuchus, is
a let-down after M10 and M12, but it is not a bad cluster
in its own right. It is, however, rather hard to locate
within the huge and amorphous body of Ophiuchus.
Technically, M14 is smaller than M10 or M12, but it appears
much bigger, because it lacks a concentrated core. The
large apparent size and low surface brightness make M14
rather attractive under suburban skies or darker, but
M14 suffers badly under heavy light pollution because
of its low surface brightness.
The easiest way to find M14 is to start at Beta Ophiuchi,
a reddish mag 2.7 star, but it is an arduous 8-degree
starhop from there to M14. One could try aiming 2/5 of
the way from Beta Oph to Xi Serpentis, but this is a bit
of a long shot considering that M14 is not very prominent
at low power. Also, Xi Ser may be hard to see given its
southerly declination and its modest magnitude of 3.5.
Under urban skies, M14 is rather elusive both in my 70mm
scope and in my 178mm scope, showing best with averted
vision in both cases, although it is perceptible with
direct vision in the larger scope. It appears quite
similar in both scopes, as a large diffuse circle about
4' to 5' in diameter.
Under suburban skies, M14 is actually easier to see in
my 7x35 binoculars than M10 or M12, because of its large
size. It is fairly easy to see in my 70mm scope under
suburban skies and quite prominent in my 178mm scope.
In both cases, it is quite large and diffuse, about 5'
in diameter. The 178mm scope also shows a vague 2.5'
core. The appearance is not altered much by magnification,
so M14 does best at medium power, especially in the
larger scope, which allows one to see its setting in
a rather attractive field of bright background stars.
M6 and M7
M6 and M7 are two of the brightest open clusters in
the sky, a welcome change from the globular clusters
of Ophiuchus. Both objects lie quite far south; in
fact, M7 is the southernmost of all the Messier objects,
and must have been a logistical challenge for Messier to
observe from Paris, where it rises barely 6 degrees above
Despite their southerly declination, both clusters are quite
striking even for northern observers; in fact, Messier
reported seeing both of them naked-eye, a feat that I
can replicate easily at my latitude under dark skies.
Unfortunately, light pollution makes a naked-eye sighting
ulikely in urban or suburban skies at latitude 42N.
M6 and M7 lie a little under 4 degrees from each other,
just off the end of Scorpius' tail. The final three stars
of the tail are quite bright, especially Lambda Scorpii,
the last star, at mag 1.7. Unfortunately, at my latitude
of 42N, it requires a low southern horizon to get a good
view of the tail. M7 lies halfway from Kappa Scorpii,
the next-to-last star in the tail, to mag 3.0 Gamma
Sagittarii, and if that fails, there are ample stars
in the area to support star-hopping. When in doubt,
M6 is most easily located by star-hopping from M7.
M7 is the second brightest of all the Messier objects,
behind M45, and also the second easiest cluster to resolve.
M44 rivals it closely in both regards, but I find M7
tightr and more shapely than M44. Like M44 and M45, M7
has been known since Classical times, being recorded in
Ptolemy's Almagest. In fact, M7 is sometimes called
M7 is immediately recognizable and faily well resolved
with even the slightest optical aid, even under urban
skies at my latitude of 42N. It shows about 10 stars
using my 7x35 binoculars in the suburbs, and shows at
least twice that number at 40X in my 70mm scope. Most
of the stars are packed into a 30' circle, but there are
a few outliers in a much looser formation that are
probably also part of the cluster. The 178mm scope is
somewhat over-powered for M7, which is not especially
rich in fainter stars, and which requires a fairly large
field of view for proper appreciation.
M6 is fourth-brightest among the Messier clusters, but it
is much fainter and smaller than M7. Morphologically, it
is quite different from M7, with the stars more numerous
and denser, but also much fainter on average. Under
surburban skies, I can resolve three stars in my 7x35
binoculars, and the remainder form into an unmistakable
haze. I have not positively identified M6 in my 7x35
binoculars under urban skies, where the haze is swallowed
by the bright sky glow along the horizon and even the
brightest stars are hard to resolve.
M6 appears well resolved in my 70mm scope at 60X both
under urban and suburban skies, but a look through the
178mm scope reveals the fact that there are many stars
too faint to see in the smaller scope. Regardless,
M6 appears quite rich through both scopes. The
brighter stars famously trace the outline of a
butterfly, giving this its popular name of the
Butterfly Cluster. The bright red variable star
BM Scorpii lies at the tip of the E wing.