There are 24 Messier objects between RA 18 and RA 21, the
second-richest octile of the Messier list after the one
that includes the Virgo Cluster. The abundance of Messier
objects is due to the fact that this part of the sky
contains the widest, richest, and brightest part of the
Milky Way, with some of the finest star clusters and
nebulae in the sky.
These late-summer Messier objects are both a blessing and
a curse for urban and suburban observers north of latitude
30N or so. The blessing is that unlike the faint galaxies
of spring, many of these are bright showpiece objects that
are spectacular even through heavy light pollution. The
curse is that they are heavily concentrated at southerly
declinations, where they never really climb out of the
soup of light pollution along the horizon.
In addition, they are well-placed only during the summer,
when the nights are at their shortest and the logistics
of observing are most problematic. But they are not quite
as bad in this regard as the objects between RA 15 and RA 18,
at least not for people who do most of their observing in
the evening rather than in the pre-dawn. These objects
become well-placed in the evening sky just as the nights
start to become significantly longer, so although they
are slowly slipping out of grasp, the ever-earlier
evenings give you a chance to admire these showpiece
objects well into autumn, if you start as soon as the
sky gets dark.
For instance, M8, the quintessential late-summer object,
is at its highest at 10PM daylight time around August 1,
which is around when the sky becomes fully dark at my
latitude of 42N. One month later, the sky is fully dark
at 9PM, and M8 is only an hour past its prime. On
October 1, the sky is fully dark at 8PM, and although
M8 is then 2 hours past its prime, it is still moderately
well placed, just 5 degrees lower than optimal.
For convenience, I have included M23 in this section,
despite the fact that its RA is three minutes shy of
18:00, because it clusters naturally with the other
objects in Sagittarius. I have tranferred the three
eastermost objects (M29, M72 and M73) to the early-fall
section to augment the measly five objects that actually
fall properly in that section, between RA 21 and RA 23:59.
Here, then, are the late-summer Messier objects:
For a key to this table, see
Key to the Tables.
In the unlikely event that you tire of the objects in this
section, M13 and M92 remain reasonably well-placed in the
evening sky throughout the summer for observers in the North
Temperate Zone, and several of the objects in the early-
autumn section lie quite far north, and rise reasonably
high fairly early in the summer. As for galaxies, the
king of them all, M31, begins to rise in the eastern sky
just as M51 is disappearing in the western sky.
M23 is a delightful open cluster in its own right, but
its primary significance for me is as the forerunner of
the magnificent Sagittarius Messier objects, and of the
summer Milky Way in general. I love observing the
distant galaxies of spring, but I am always glad when
they yield place to our own galaxy. Lying on my back
on a warm summer night, I can see far more detail in the
Milky Way with my unaided eyes than I can see in any
other galaxy with the largest telescope I have ever used.
To locate the Sagittarius Messier objects, you must first
locate Sagittarius itself, which is not as easy as it should
be under bright skies at my latitude of 42N, due to its
southerly declination and the fact that many of its
signature stars are only third magnitude. Although
Sagittarius means "archer", most modern astronomers
prefer to picture it as a teapot, with the handle on
the east and the Milky Way issuing out of the open
spout on the northwest. The only genuinely bright stars
in the constellation are mag 2.1 Sigma in the handle and
mag 1.8 Epsilon at the SW edge of the base. The key
stars for locating the Messier objects are Lambda,
Delta, and Gamma on the top of the kettle, all mag
2.7 - 3.0.
M23 lies a little under 2/3 of the way between Lambda Sgr
and Xi Serpentis, but that is a long enough stretch to
make it hard to locate M23 by the point-and-shoot method.
It helps a lot if you can see Mu Sgr (mag 3.8) partway
between Lambda and M23. Failing that, it is a long
6-degree starhop from Xi Ser or a very long 10-degree
starhop from Theta Oph or Lambda Sgr.
In my 7x35 binoculars, M23 is visible as a faint, subtle
cloud of light in under a suburban sky, but invisible
from the city. In my 70mm scope, it is barely visible
at low power but quite attractive at 60X both in the
city and in the suburbs, showing a few stars with direct
vision in the city and about a dozen in the suburbs.
In both cases, the directly visible stars are
supported by a much richer background of stars that
can be seen only with averted vision.
In my 178mm scope, M23 is fairly well resolved at all
powers both in the city and in the suburbs, showing
several dozen stars in a 25' circle. Because extra
magnification is not needed to bring out the faint
stars, as it is in the smaller scope, M23 shows best
at modest power, around 40X, where enough of the
background is visible to set the cluster off well.
M8, the Lagoon Nebula, is a close rival of M42 and M45
as my very favorite Messier object to view with small
instruments under dark skies. Unfortunately, the
nebulosity that makes M8 so magnificent is hurt badly
by light pollution, especially at my latitude of 42N,
where M8 never rises higher than 24 degrees off the
M8 is the same kind of object as M42, a dense cloud of
gas which is actively giving rise to new stars. M8 appears
somewhat fainter than M42, but that is due entirely to
the fact that it is much farther from us, some 5000 light
years distant as opposed to 1500 for M42. In fact, M8
is considerably larger and more active than M42.
M8 is a very large object, listed as 90' by 40' by many
sources, but the portion that is visually observable is
much smaller; the bright part of the nebulosity is no
more than 30' in the E-W direction and 20' N-S.
Somewhat E of center is a cluster of about two dozen
stars, mostly ninth and tenth magnitude, arranged in a
crude rectangle about 10' from NE to SW and 7' in the
narrower axis. This cluster has the separate designation
Encircling NGC 6530 is a ring of stars considerably brighter
than any in the cluster proper, the brightest of which is
the mag 6.0 star Sagittarii directly W of the cluster.
This star, and its companion Herschel 36 to the WSW, are
the primary illuminators of M8, just as star C in the
Trapezium is the primary illuminator of M42. Like the
Trapezium stars, 9 Sgr and Herschel 36 are O-type stars
emitting the great majority of their energy in the
ultraviolet spectrum, and causing the hydrogen and oxygen
in the gas cloud to fluoresce in a few specific wavelengths
of visible light.
Even brighter than 9 Sgr is mag 5.4 7 Sgr 15' to the WNW.
7 Sgr is flanked by a few other brightish stars which
appear to form a sparse mini-cluster in their own right.
The nebulosity is brightest around 9 Sgr and Herschel 36,
especially in very small and intense patch about 1' in
diameter around the latter star. The star cluster NGC 6530
is also suffused in a somewhat fainter nebulosity, and those
two patches of nebulosity are connected by an arch to the N.
In the middle of all of that is the famous dark patch, like
a patch of water surrounded by a coral reef, which gives the
Lagoon Nebula its name. There is also a very faint nebulosity
surrounding the whole object, but it is quite invisible under
urban or suburban skies, even with a nebula filter. A few
isolated bright patches do show through under good conditions,
notably near the mag 7 star E of NGC 6530 and around 9 Sgr.
M8 is very obvious to the naked eye under dark skies,
looking like a small disjoint piece of the Milky Way
some distance W of the main body, and somewhat brighter.
Even under suburban skies, I can see M8 fairly easily
with my unaided eyes, although not in the city.
I have never been sure whether I am actually seeing
the nebulosity or the cluster of stars contained within.
If you cannot see M8 directly, which is likely, it is
a moderate 4-degree starhop from mag 3.8 Mu Sagittarii,
or you can locate it by the fact that Mu Sgr and M8 are
equidistant from Lambda Sgr. If you cannot see Mu,
you might try extending the line from Phi Sgr through
Lambda and bending slightly S, or you can starhop 5.5
degrees from Lambda.
Under urban skies at 42N without a nebula filter, the
view of M8 is dominated by the stars rather than the
nebulosity. Even my 7x35 binoculars show the brighter
stars easily, such as 7 Sgr and 9 Sgr, and they show
NGC 6530 as a fairly bright cloud with a few stars
peeking through. In my 70mm scope at 60X, NGC 6530 is
resolved into about a dozen stars, and the nebulosity
near 9 Sgr and surrounding the cluster is faintly visible.
NGC 6530 is well resolved at all powers in my 178mm scope,
with higher powers showing more detail and lower powers
giving a better overview. 60X may be the best compromise.
Again, the embedded nebulosity is visible, still faint but
much bolder than in the 70mm scope.
Adding a nebula filter under urban skies changes the view
completely. The stars become much less evident, and the star
cluster NGC 6530 nearly disappears in my 70mm scope. The
nebulosity, however, becomes very much bolder and brighter,
and the Lagoon shape becomes quite obvious, which is not
true without the filter.
M8 does much better under suburban skies; the nebulosity is
quite obvious even in my 7x35 binoculars, and is prominent in
both my scopes even without a filter. Using the 178mm scope
with the filter, the nebulosity is overpowering in the brighter
sections, and shows a wealth of fine detail throughout.
M20 and M21
Moving north along the axis of the Sagittarius Milky Way, the
next Messier objects after M8 are M20, another bright nebula
with embedded stars, and M21, a rather unremarkable open cluster.
M20 is a magnificent object under dark skies, especially in
large telescopes, but its nebulosity is much more subdued
than M8's, and it suffers very badly from even modest light
M20 and M21 are mostly easily reached by starhopping from
the much more prominent M8, or simply by moving the telescope
north two degrees. All three objects (M8, M20, and M21)
are visible simultaneously in a rich-field telescope at
low power, forming what many people consider to be the
single finest wide telescopic field in the whole sky.
M20 and M21 lie at opposite ends of Webb' Cross, a wonderful
asterism of stars from mag 6 to mag 8 arranged like a cross
with the long arm faintly curved and the short arm,
consisting of the three brightest stars, an arc severely
concave to the S. The whole formation is about 40' long,
and M21 surrounds the northernmost star, while M20 surrounds
the whole S section. The cross is quite obvious in my 7x35
binoculars, but M21 and M20 show only as vague glows in that
instrument under suburban skies, and not at all under urban
M21 is rather small and sparse, and the stars have a wide
range of brightness, from the central mag 7 star down to
mag 12 or 13. It is also set against a fairly rich
background, which makes it look even less prominent.
Many of the stars are arranged in a nearly perfect circle
about 3' in diameter with the mag 7 star on the S and a
complete void in the middle, which gives the cluster a
rather unusual appearance once it has been detected.
The remaining stars are scattered loosely in a circle
some 10' to 15', and it is quite impossible to say where
the cluster ends.
M21 is reasonably well resolved in my 178mm scope at high power,
even under urban skies, and enough stars show in the 70mm scope
under suburban skies to make the flesh the cluster out. Only
half a dozen stars are visible in the 70mm scope under urban
skies, and they do not add up to a convincing cluster.
Under urban skies, M20 is quite invisible in my 70mm scope, and
I am not 100% sure that I have seen it in my 178mm scope either.
The best place to look is around the lovely double star Herschel
40, which forms the S end of Webb's Cross. If I look hard, I
see just a hint of nebulosity, maybe 5' across, surrounding the
star. The nebulosity -- real or imagined -- remains but is not
improved by my nebula filter.
M20 is much more definite under suburban skies, but is still
only a pale shadow of its true self as seen under dark skies.
Again, it appears as a 5' circle around Herschel 40, faintly
present in my 70mm scope and fairly obvious in my 178mm scope.
In both scopes, a nebula filter makes the nebulosity much
more definite, but it does not make it seem any larger or
show any more detail.
I have never been able to see under suburban skies any of the
wonderful detail that makes this nebula famous, notably the
15' circle around Herschel 40 split into three or four lobes
by striking dark lanes, which gives this object its popular
name the Trifid Nebula, famous from science-fiction horror
novel and movie. I have also never had a hint in city or
suburbs of the secondary nebulosity some 15' to the N,
separated by a wide dark lane from the primary nebulosity.
Moving 5 degrees NNE along the galactic axis from M20
and M21, we encounter M24, one of the most unusual
objects in the Messier list. Indeed, this is technically
not an object at all. Messier called it a star cluster,
but that implies a collection of stars which are
physically related and bound to each other by gravity,
which is not true for M24. Instead, M24 is a star cloud,
a rich portion of the inner Milky Way which happens to be
visible to us because of a gap in the dust clouds that
normally prevent us from seeing far along the galactic
plane, particularly towards the center, where stars, gas,
and dust are all most dense. If not for the dust clouds,
this whole quadrant of the sky would be ablaze with light,
as M24 is.
M24 is sometimes called the Small Sagittarius Star Cloud.
The Great Sagittarius Star Cloud is the "steam" that
issues from the spout of the teapot, N of Gamma and
Delta Sagittarii, some ten degrees S of M24. The Great
Sagittarius Star Cloud is even more remarkable than the
lesser cloud, being a portion of our galaxy's central
bulge, again showing through a gap in the celestial clouds,
whereas M24 is part of one of the inner spiral arms.
The actual center of the Milky Way lies some distance
WSW of the Great Sagittarius Star Cloud, but it is
completely blocked from us in the visual spectrum by
dense clouds of dust. It does shine through in X-ray
and radio frequencies, where it is called Sagittarius A.
Like M8, M24 is very obvious to the naked eye under dark
skies, and visible but somewhat subtle in the suburbs at 42N.
Again like M8, it appears like a piece of the Milky Way,
not as clearly separated from the main body as M8, but
much larger than M8, and much brighter than most of the
If M24 is invisible to the naked eye, it can be found some
2.5 degrees N of Mu Sagitarii, assuming that that mag 3.8
star is visible. Failing that, it can be found 2/5 of the
way from Lambda Sagittarii to Nu Ophiuchi
M24 is huge by telescopic standards, some 2 degrees along
the long axis, from NE to SW, and 30' to 45' across. It
is best seen at very low power under dark skies in an
instrument large enough to fit the whole thing lengthwise.
But it can still be appreciated well in a scope whose
maximum FOV is in the 1 - 2 degree range by scanning the
object lengthwise. A 1-degree FOV fits just enough of the
relatively sparse background on either side of M24 so that
one can appreciate M24's richness and separate identity.
Unfortunately, under urban skies, the background is filled
with light pollution rather than darkness, and enough of
M24's stars are blotted out to detract greatly from the
overall impression. M24 does appear as a markedly rich
star field in my 7x35 binoculars, in my 70mm scope at 16X,
and in my 178mm scope at 28X, but the true grandness of
this star cloud is lost.
M24 fares much better under suburban skies, where even my
7x35 binoculars are big enough to resolve a fair number of
stars, and where the contrast between M24 and the background
is much more prominent. Again, it looks best at the lowest
possible power in both of my scopes.
M16, M17 and M18
Just N of M24 lie three closely spaced Messier objects:
M18, M17, and M16, moving S to N. M16 happens to be just
across the constellation boundary into Serpens, but I think
of all three objects as part of the Sagittarius Milky Way
The three objects all fit together with M24 in the field of
most hand-held binoculars, and my 70mm F/6.9 scope at lowest
power is just able to fit the three objects without M24.
M18 is by far the least interesting of the three objects.
It is a perfectly respectable open cluster, and might even
seem rather attractive in other parts of the sky, but it is
totally overwhelmed by its neighbors.
M17, the Swan or Omega Nebula, is an emission nebula like M8
or M42, and every bit a match for those two. Its surface
brightness is not as high as the Hughenian area of M42 or
the intensely bright patch in M8 near 9 Sgr, but the bright
part of M17 is much more extensive than the bright part of
either of those other nebulae. Like M8 and M42, M17 is giving
birth to a population of brand new stars, but these are
entirely shrouded by gas and dust, and cannot be seen in
the visible spectrum. Infrared photographs, however,
reveal a budding star cluster within the nebula.
M16, sometimes called the Eagle Nebula, is yet another
star cluster embedded in nebulosity, but it is at the
opposite end of the spectrum from M17. In M17, the
nebulosity is bright and bold, but the cluster is
invisible. In M16, the cluster is prominent and
attractive, but the nebulosity is subtle even under
dark skies, let alone in city or the suburbs.
Once any member of this triplet has been found, the other
two are easy to locate by moving the scope slightly S or N.
They are also all easy to find off the N end of M24. I
generally find M16 the easiest of the three to pick up in
binoculars or a finderscope, especially under heavy light
pollution, but M17 is also quite easy to see with even
the most modest optical aid under all but the worst skies.
Both objects show at low power as unresolved patches
Like the other objects of the Sagittarius Milky Way, these
are all surprisingly far from any truly bright star despite
being located in the one of the richest parts of the sky
as measured by the density of stars mag 6 and fainter.
When looking for them under skies to faint to see M24
directly, your best bet may be to starhop from Nu Ophiuchi,
but the hop is long and arduous and the anchor star is
not terribly bright, at mag 3.3.
M18, the southernmost of the three, has two different aspects
under suburban skies or darker. At very low power, as in 7X
binoculars or at low power in my 70mm scope, it shows as a
small, faintish cloud of light, with only the central mag 8.7
star possibly visible. At 60X in my 70mm scope, I can see
half a dozen stars around that central star in a rough 7'
circle, and high power in my 178mm scope brings in perhaps
another dozen fainter stars.
Under urban skies, the cloud-of-light view is lost entirely,
making M18 invisible in my 7x35 binoculars or in my 70mm
scope at low power. At 60X in my 70mm scope, I can make
out the brighter stars with averted vision, and M18 is
adequate although unimpressive at 120X in my 178mm scope.
Under urban skies, M17 is readily visible in both my scopes
without a filter, but far more impressive and detailed with
the aid of a nebula filter. The same is true under suburban
skies, but of course both the filtered and unfiltered views
are improved by the darker skies.
The most prominent feature of M17 is a broad, bright bar of
light running some 10' from WNW to ESE, and about 3' wide.
This is what shows in the smallest instruments and in the
worst conditions. A second, fainter bar of nebulosity
running roughly N-S joins the first at the WNW end, making
a striking checkmark shape. Under darker skies, you can
see that the vertical bar bends to the W, forming the
neck of the Swan as seen in an inverting telescope, and
you can also see some much fainter nebulosity surrounding
the whole, but I have never seen these in city or suburbs
even with the aid of a nebula filter.
In the city, without a nebula filter, M16 shows as a star
cluster -- a very attractive cluster, but utterly without
nebulosity. This fact is actually more apparent in my 178mm
scope than in my 70mm scope, because the former scope resolves
M16 well, whereas the latter shows enough stars near the edge
of resolution to add up to some false sense of nebulosity.
The cluster consists of five mag 8 and mag 9 stars, two very
close to each other on the W edge, with some twenty fainter
stars filling the intervening space, all in a 6' circle.
Under suburban skies, the star clusters shows much as in
the city, but a faint nebulosity is visible in my 70mm
scope without a nebula filter, and more prominent, but
only slightly so, in the 178mm scope. The nebulosity
is only really visible around the mag 9.5 star in the NW
corner and its mag 11 companion.
Adding a nebula filter changes M16 dramatically. The
cluster becomes much more subdued, and pretty much
disappears in my 70mm scope under urban skies. In
the city, the filter gives much the same view of the
nebulosity that one gets without the filter in the suburbs,
a faintish cloud in the NW corner. In the suburbs with
the filter, the nebulosity in the NW corner becomes quite
bright and prominent, and fainter tendrils stretch out
from there to suffuse the entire cluster.
Even under the darkest skies, the nebulosity in M16 is a
difficult subject for the visual observer. But for
astrophotographers and imagers, this is one of the most
spectacular subjects in the sky. Most famous is the
famous Pillars of Creation image from the Hubble Space
M25 frames the Sagittarius Milky Way on the E as M23 frames
it on the W. M25 is another fine open cluster, but whereas
M23 is rich in moderate and faint stars, M25 is a fairly
coarse agglomeration of bright stars.
M25 is a 4.5-degree star-hop from Mu Sagittarii, or if you
are already pointing at M24, you may be able to find it by
moving due E. It may also be visible to the naked eye
under good suburban skies.
M25 shows easily in my 7x35 binoculars as a bright patch,
with several stars resolved, especially under suburban skies.
The telescopic view is best in my 178mm scope, but the 70mm
scope does nearly as well, and the cluster is relatively
impervious to light pollution, because most of the stars
are quite bright (mag 7 - 9). In all cases, the view is
best at roughly 60X. Higher powers constrict the field
of view too much to set this fairly large and coarse
cluster off from the rich background, and lower powers
fail to do justice to the tight clump of faintish stars
near the center of the cluster.
M25 contains a little knot of ten stars near the center
in an area about 5' x 2' elongated E-W with a pretty arc
of five or six stars just S of that, and a looser arc of
stars near the S border of the cluster.
M22 and M28
Just as Ophiuchus contains a wealth of globular clusters W
of the main axis of the Milky Way, so Sagittarius contains
a fine collection of globular clusters trailing the Milky
Way to the E, and the finest of these by far is M22.
Nearby M28 is another fine globular cluster, but very
much eclipsed by its magnificent neighbor.
Let us start with M28, the westernmost and lesser of these
clusters. M28 is very easy to find, just one degree NW of
mag 2.8 Lambda Sagittarii.
Under urban skies at latitude 42N, M28 is not exactly hard
to see in my 70mm scope, but it is not at all prominent,
possibly requiring averted vision. In my 178mm scope
under urban skies, it is obvious at all powers, showing
at 120X as a small circle of light about 1.5' to 2' in
diameter, strongly concentrated towards the center.
Under suburban skies, M28 is bright and concentrated, almost
starlike in my 70mm scope at 40X or 60X. In the 178mm scope,
in shows a bright 2' core inside a halo perhaps 4' across,
fading out gently at the edges.
M22 is a little harder to locate but much brighter, bigger,
and easier to see. If you take a line from Gamma Sagittarii
through Lambda Sgr and continue it another 2.5 degrees ENE
of Lambda, you reach M22. M22 is fairly easy to see in my
7x3 binoculars, although it is somewhat washed out but
light pollution at my latitude of 42N, especially under
In my 70mm scope, M22 is obvious at all powers under all skies,
showing about 4' - 5' across under urban skies and more than
6' across under suburban skies at 60X. The brightness is
fairly uniform across the face of the cluster, but moderately
concentrated towards the center. It is distinctly grainy
under suburban skies, and resolves a few stars with averted
vision under dark skies.
In my 178mm scope, M22 is magnificent at all powers under
all skies. Several stars are resolved at 120X under urban
skies and many more peek through intermittently. Under
suburban skies at 120X, M22 shows at least 7' across, but
fades out vaguely to hint at a much larger disk. The
central area is very bright, glowing as if on fire. I
can pin down the location of two dozen stars, and far
more are visible intermittently.
M54, M69 and M70
Three Messier globular clusters lie along the S edge of
the Teapot asterism. Moving W to E they are M69, M70, and
M54. None of them can be resolved easily in medium-sized
scopes even under dark skies, let alone under urban or
suburban skies, but they are all interesting and attractive
objects. M54 also has the distinction of being the only
globular cluster in the Messier list which arguably belongs
to a galaxy other than the Milky Way.
Epsilon Sagittarii, the star at the SW corner of the Teapot,
is the brightest star in the constellation at mag 1.8, making
it quite prominent even under urban skies at latitude 42N,
where it never rises more than 14 degrees off the horizon.
M69 lies 2.5 degrees to the NE, in the direction of Phi
Sagittarii (mag 3.1), and M70 lies 4.5 degrees ENE, nearly
halfway to Zeta Sagittarii (mag 2.6). M54 lies 1.5 degrees
WSW of Zeta, just N of the line connecting that star to Epsilon.
Nominally, M70 is slightly fainter and very slightly larger
than M69, but according to my visual impressions, M70 is
quite a bit larger, with significantly lower surface
brightness, and quite a bit harder to see under heavy
light pollution, especially at low magnifications.
In my 70mm scope at 60X, M69 is fairly easy to see, but
M70 is elusive, especially under urban skies, where it
requires concentrated effort with averted vision.
M69 is 3' or under, with a concentrated core, while M70
is a vague, about 4', uniformly faint across the disk.
Both clusters are much easier to see in my 178mm scope
at 80X to 120X, even fairly bold and attractive, but they
do not show much more detail than in the smaller scope.
M54 is much more remarkable in every way. This globular
cluster is inherently very bright, but it is by far the
most distant of all the Messier globulars, some 70,000
light years distant, on the far side of the galactic core.
Recent analysis indicates that M54's motion, and the motion
of many nearby stars, is radically different from the
prevailing motion of that portion of the Milky Way.
This is attributed to the fact that those stars, and M54,
are actually part of a small galaxy, the Sagittarius Dwarf,
which is currently colliding with the Milky Way. In all
probability, the Sagittarius Dwarf will not survive the
collision; its stars will be swallowed up in the Milky
Way's disk, while M54 will be added to the halo of
globular clusters circling the Milky Way's core.
M54's great distance makes even its brightest stars appear
quite faint, so M54 is quite hard to resolve even in fairly
large amateur telescopes under good conditions, and quite
impossible with medium-sized scopes under urban or suburban
skies. However, M54 is quite bright and concentrated,
giving it a high central surface brightness which makes it
quite easy to see even under heavy light pollution.
In both my 70mm scope and my 178mm scope, M54 is readily
visible at all powers under all skies, but it is quite small,
nearly starlike. The best views are at fairly high powers,
60X in the 70mm scope or 80X to 120X in the 178mm scope.
It shows a vague disk about 1' across under urban skies,
and maybe 2' across under suburban skies.
Trailing far E of the Milky Way and the Teapot, in a part of
the sky otherwise devoid of interesting deep-sky objects, lies
the remarkable globular cluster M55. M55 appears almost as
large as M4, and has even lower surface brightmess, making
it quite prominent under dark skies but difficult to see
under heavy light pollution, especially considering its low
maximum altitude above the horizon for northern observers.
Finding M55 is a major nuisance even under dark skies; it is
nowhere near any plausibly bright star. I find the best
strategy to be the arduous 8-degree starhop from Zeta Sagittarii.
I can resolve M55 fairly easily in my 178mm scope under dark
skies, but I have never seen any hint of resolution under
urban or suburban skies. Due to its immense size and low
surface brightness, M55 under light pollution shows best at
fairly modest magnifications, around 30X in my 70mm scope
and 60X in my 178mm scope. As with other large, diffuse
objects, the view varies more due to sky brightness than
In the city, M55 is difficult to see even with averted vision
in both of my scopes, showing up best when I pan around the
area so that M55's apparent motion catches my eye. It appears
enormous (over 7') and vague.
M55 is much easier to see under suburban skies, but it still
appears both vague and faint. Again, it is enormous, around
10' across, nearly as big as the distance between the
prominent pair of mag 8 stars 45' to the NNW.
M11 and M26
Returning to the main axis of the Milky Way, we move north
in the Scutum star cloud, an area full of magnificent
deep-sky objects including two open clusters catalogued
by Messier: M11 and M26. M26 is rather attractive under
dark skies, but it is the faintest open cluster in the
Messier list, which makes it disappointing under bright
skies and/or in small instruments. M11, by contrast,
is extremely bright and attractive in all instruments and
under all skies. Indeed, many people consider it to be
the most beautiful open cluster in the sky.
For all of its wonderful deep-sky objects, the constellation
of Scutum is a sorry affair, composed of four fourth-magnitude
stars in a nondescript pattern. It is unconvincing under
dark skies and may be entirely invisible under urban skies.
In general, I find it easier to locate objects within the
Scutum star cloud off of Auqila to the NE. Aquila can be
spotted immediately by brilliant first-magnitude Altair
with its attendants Tarazed (Gamma Aquilae, mag 2.7)
and Alshain (Beta Aquilae, mag 3.7) to the NNW and SSE
respectively. The four third-magnitude stars making up
the rest of the outline of Aquila (the Eagle) are less
prominent, but they make a distinctive and attractive
The tail of Aquila is composed of three stars arcing
SSW: Lamdba Aquilae (mag 3.4), 12 Aquilae (mag 4.0)
and Eta Scuti (mag 4.8) just over the border into Scutum.
One or more of them may be invisible to the naked eye
under urban skies or poor suburban skies, but the
arc should be striking in binoculars or a finderscope.
If you continue from Lambda Aql through Eta Sct and
then on for another 1.5 degrees, you reach M11.
Continuing from Lambda through 12 Aql and on for
another 5.5 degrees, you reach M26. Alternatively,
M26 is an easy starhop from Eta Sct via the line
of 5th and 6th magnitude stars S and SW of Beta
Sct, and then back to M26 via bright Epsilon and
M11 in some ways resembles a globular cluster more than
an open cluster. It contains hundreds of stars packed
very tightly, but all of the stars are fairly faint, and
the range of brightness among the stars is fairly narrow.
Therefore, like globular clusters, M11 appears as an
intense but unresolved patch of light in very small
instruments and at low magnifications. Indeed, M11 is
visible as a patch of light under virtually any skies
with almost any optical aid. It is quite obvious in
my 7x35 binoculars under urban skies.
Only three stars are clearly resolvable in my 70mm scope
at 60X: a mag 8.6 star near the center and a pair of 9th
magnitude stars near the SE edge. Under suburban skies,
a few other stars occasionally pop out with averted vision,
particularly on the S side. All of this is set against
a lovely bright glow of unresolved stars about 8' square.
M11 is breath-taking in my 178mm scope. At low power, it
shows as a fan of light stretching W of the bright central
star, scattered with faintish stars, and with a few other
stars set around. At 120X, the fan of light resolves into
a huge number of stars, too many to count. Despite the
superficial similarity to a globular cluster, M11 is much
easier to resolve, and lacks the classic circular symmetry.
M26 is like a radically scaled-down version of M11. Like
M11, it has a bright central star, but it is a magnitude
fainter than M11's. Like M11, M26 contains a scattering
of medium-bright stars and a dense swarm of faint stars,
but the latter are genuinely faint in M26 -- near the
limit of my 178mm scope under dark skies -- and nowhere
near as dense as in M11.
With a total magnitude of only 8.0, M26 is quite invisible
both in my 7x35 binoculars and in my 70mm refractor under
urban skies. The central star is indeed visible in the
small scope, and perhaps one or two of the surrounding
stars, but that does not add up to a cluster. The bright
sky background camouflages the haze of light that would
otherwise result from the unresolved stars.
Much to my surprise, M26 is visible in my 7x35 binoculars
under suburban skies, showing as a tiny but fairly bright
patch of light forming a nearly perfect isoceles right
triangle with Delta and Epsilon Scuti. The view is quite
similar at 16X in my 70mm scope, but using averted vision
at 60X, I can resolve several stars in addition to the
M26 does far better in my 178mm scope at 120X, which is
enough aperture to resolve about a dozen stars under urban
skies, and somewhat more under suburban skies. Nonetheless,
the stars are a little too scattered to form a completely
convincing cluster, especially under urban skies.
M27 and M71
Following the galactic axis far to the north of the objects
we have discussed before, we come to two more Messier objects:
the faint and unusually sparse globular cluster M71 in Sagittae,
and big, bright planetary nebula M27 in Vulpecula. Although
these objects are far E of Sagittarius, they are also far
enough N so that they reach a reasonable altitude earlier
for most observers in the North Temperate Zone, and they
linger well into autumn.
These objects are placed in a rather inscrutable part of the
sky. Vulpecula, in particular, is one of the sorriest
constellations in the sky, composed entirely of faint stars
arranged in no recognizable pattern. Sagittae is compact,
and very shapely if you can see it, but two of its four
essential stars are only mag 4.5 and the brightest is only
mag 3.5, making it a challenge for urban and suburban
observers. Fortunately, it is small enough to fit
completely into the field of 7X or 10X binoculars, and
it is well worth a look.
It is easy to locate the general area of the sky between
brilliant first-magnitude Altair on the S and Albireo
(Beta Cygni, mag 3.1) on the N. Albireo, by the way,
is generally considered to be the most spectacular double
star in the sky, readily split at 15X or higher, with
wonderful contrast between the golden primary star and
the blue secondary star. Having done that, look hard
for Sagittae halfway between Altair and Albireo, and
slightly E. Once this is done, M71 is very easy to locate
halfway from Delta Sagittae to Gammma Sagittae, and
just 20' from (telescopically) bright 9 Sagittae.
Delta Sge, Epsilon Sge, and M27 form a very obtuse,
nearly isoceles triangle with Gamma at its apex.
M71 is unusually sparse for a globular cluster; in fact,
it was usually considered to be an open cluster until the
last few decades. The small number of stars gives M71 one
of the lowest total brightnesses of any Messier globular
cluster, but the individual stars are fairly easy to
In my 70mm scope, M71 shows best at 40X, where it appears as
a faint cloud of light, about 3' - 4' across, best with averted
vision but still perceptible with direct vision, even under
urban skies. It is slightly extended NE - SW, with a faint
extension to the N.
In my 178mm scope, M71 shows much as in the 70mm scope, but
there are hints of resolution at 120X under urban skies, and
at least a dozen stars are clearly perceptible with averted
vision under suburban skies.
M27 is a completely different animal, the brightest planetary
nebula in the sky by a fair margin. M27 also has high surface
brightness, allowing it to show fairly well under heavy light
pollution. M27 is readily visible, although surprisingly small,
in my 7x35 binoculars under suburban skies but quite difficult
under urban skies.
Like most planetary nebulae, M27 responds well to a narrowband
nebula filter, but even if you own such a filter, M27 should
be observed both with it and without it. The filter brings
out certain aspects of the nebula, but others are best
observed without it.
In my 70mm scope, M27 shows best at 60X, where it appears as a
rectangle with rounded corners, extended NNE - SSW, with a hint
of scalloping along the long sides.
The 178mm scope brings out the scalloped shape much more strongly,
making it obvious why this is sometimes called the Dumbell Nebula.
To me, it is more reminiscent of an apple with large bites taken
out of the sides. The view is best at 80X to 120X. Using my
narrowband filter, the bites on the sides cease to be hollow,
and instead become filled with a faint nebulosity, especially
under suburban skies. In fact, the faint nebulosity extends
farther from the center than the bright apple part, so whereas
without the filter M27 is about 5x3 extended NNE - SSW, with
the filter it is about 8x5 extended WNW - ESE.
M56 and M57
The small constellation of Lyra contains two Messier objects:
M57, the Ring Nebula, which may be the most famous of all
planetary nebulae, and the modest globular cluster M56.
These are the northernmost of the late-summer Messier objects,
and also placed fairly far W, so that they reach reasonable
altitude quite early in the summer, or even in the late spring.
Few people go out of their way to observe M56, but M57 is one
of the great showpieces of the heavens, and with the highest
surface brightness of any Messier object, it is a particularly
attractive target for urban and suburban observers.
The constellation of Lyra is one of the most prominent and
attractive star patterns in the sky, although some of the
stars may be difficult or invisible under urban skies.
The eye is immediately drawn to Lyra by dazzling blue-white
Vega, fifth brightest star in the sky, at magnitude 0.03.
Native American legend has it that Vega and Altair are
lovers from warring tribes, immortalized in the sky but
perpetually separated from each other by the band of the
Vega forms a tight equilateral triangle with two fourth-
magnitude stars, which attaches to a nearly perfect,
elongated parallelogram to the S. Under very poor
skies, only Vega and the two 3rd-magnitude stars at
the far end of the parallelogram are likely to be
visible, and the latter may be hard. Each of the
six signature stars of Lyra is remarkable in some way;
refer to a more general guidebook like Burnham's for
more information. For now, I will only comment that
Epsilon Lyrae, Vega's partner at the far N tip of Lyra,
is the famous Double Double, resolvable into two tight
pairs of stars at 100X or higher.
M57 is extremely easy to locate 40% of the way from
Beta Lyrae at the SW end of the parallelogram to Gamma
Lyrae at the SE end. But for a deep-sky object whose
position is so tightly defined by bright stars, M57
proves surprisingly hard for many novices to find.
The reason is that M57 is very small, the smallest of
all the Messier objects. At low or even medium power,
it may be hard to distinguish M57 from a star. Look for
a star that appears slightly hairy.
In my 70mm scope under urban skies, M57 appears merely as a
tiny but bright patch of light, slightly elliptical ENE -
WSW. Under suburban skies at 60X, it begins to become
apparent that the center of the disk is hollow, especially
using averted vision.
In my 178mm scope at 120X, it is immediately obvious why
M57 is called the Ring Nebula; the doughnut shape is evident
even under poor urban skies.
M56 lies almost directly between Alberio (Beta Cygni) and
Gamma Lyrae, 45% of the way from the former to the latter.
But this is a fairly large stretch of sky, and M56 is fairly
faint, so it may be hard to locate M56 just using the
point-and-shoot method. If that fails, M56 is a somewhat
easier starhop from Gamma Lyrae than from Alberio, due to
a convenient chain of reasonably bright connecting stars.
M56 has fairly low surface brightness, making it a little
hard to see under urban skies, especially in my 70mm scope,
where it is barely perceptible with averted vision. It
shows a little better in my 178mm scope at 120X, as a small
cloud about 3' across, almost evenly bright, but fading
slightly at the edges.
M56 is considerably better under suburban skies, where it is
reasonably easy to see even in my 70mm scope. In my 178mm
scope at 120X, it shows as a bright core around 1.5' - 2',
surrounded by a very faint halo about 4' across. The whole
thing seems slightly elliptical ENE - WSW, and the core
seems to be subtly flattened on the S side. I can resolve
a few stars in M56 using the 178mm scope under dark skies,
but not under suburban skies.
Like M55, M75 floats all on its own, far from any other
notable deep-sky object or reasonably bright star.
But where M55 is enormous and vague, M75 is tiny and
I have a habitual strategy for locating M75 which seems
rather round-about but turns out to be quite efficient
in practice. It relies on the fact that the handsome
pair of mag 5 stars Rho and Pi Capricorni, close enough
to fit easily in a wide telescopic field, point almost
directly at M75. Take a line from Rho to Pi, bending
slightly N, and you pass through mag 5 Sigma Cap.
Half a degree S of Sigma, a line of three mag 8 stars
starts a sweeping arc of other mag 8 stars leading
W and S to M75.
Unfortunately, Rho and Pi Cap are usually too faint to be
seen directly under urban or suburban skies. So I find
them (very easily) by extending a line from the lovely
star pair of Alpha and Beta Capricorni which dominates
this part of the sky. Alpha is actually a pair of
stars, mag 3.6 and 4.2, separated by 6.5', which I
can sometimes but not always separate naked-eye.
M75 shows best at highish power in both my scopes,
around 60X in the 70mm scope and 120X in the 178mm.
In all cases, it shows readily as a tiny, nearly starlike
core surrounded by a small halo. Both the core and the
halo appear to grow with darker skies, with larger apertures,
and with higher magnifications.