Time sure does fly. This is my 6th summer in the
northern hemisphere. As in Australia, this also happens to be the best time of
the year to explore the summer wonders straddling the constellations of
Sagittarius and Scorpius, the center of our glorious milky way, as well as
northern sky wonders in the summer triangle. This time of the year is also the
only time the center of our home galaxy is on display, granted that it is not
as high in the sky as down south. Still so many bright objects to image and
observe, and so little time ;)
Best place to start is still at the heart of our galaxy. It
does not matter whether you are using your naked eye, small binoculars, or a
large truss tube dobsonian reflector. This is the best spot in the whole galaxy
to begin your exploration of our universe. Here we find the wondrous pairing of
M8, The Lagoon Nebula and M20, The Trifid Nebula. Both are amazing sights in
their own right and can just be observed in a single field if you have a wide
enough FOV eyepiece.
From light polluted sites, the nebulosity in M8 get overpowered by the star cluster embedded
in its embryonic cocoon. A UHC type narrowband filter will bring some its
majesty out from the background glow, but you get the best views of this object
from dark sky sites. M8 covers an amazing amount of sky from darker skies, and
the dark lane that bisects the nebula (hence the lagoon nebula moniker) stands
out in stark relieve. In fact I find there is a ripple effect from the major
dark lane, and you can make these “ripples” out under steady skies. Also the
hourglass nebula, at the heart of the nebula is best seen at slightly higher
magnifications.
While not nearly as “stunning” as the Lagoon, The Trifid Nebula
is also an easy’ish object to observe even in binoculars. With my 8x42
lightweight binoculars, the fuzz surrounding the stars is clearly evident. This
fuzz is resolved into a tri lobed structure bisected by dark lanes even in my
76mm Newtonian at lower magnifications under dark skies. In my 6” f/5
newtonian, I can make out a small island in the middle surrounding the double
star at the heart of the nebula. What makes this object interesting is that it
actually composed of three different classes of nebulae. The many “body” of the
nebula is emission in nature, bisected by dark fingers of dark nebulae. There
is also a reflection component to this object that is only visible if you
observe from dark skies without the use of a narrowband filter. From light
polluted sites, try using an 8” scope. At 100x magnification, with a UHC type
filter in place, I can make out the central island, as well as the dark lanes
with a little bit of averted vision.
Also in this area of the sky are two more “outstanding”
summer nebulas, M17, The Swan or Omega Nebula and M16, The Eagle or Little
Ghost Nebula. While further apart, if your scope can go under 20x magnification,
you may just be able to fit these two in a single field of view. Both benefit
best from dark skies. M17 shows its outer “bubble” of nebulosity from dark
skies, surrounding its inner graceful swan shape. From light polluted skies,
with an 8” scope, with a UHC type filter, this object comes alive. But to
really see detail, there is no substitute for dark skies. Under such skies, dark
lanes crisscross the body of the swan, and I get the feathery texture effect
down the back of the swan. Also the dark nebula in the neck region is fairly
obvious.
Like The Swan, M16 looks best under dark skies as well, but
this one suffers more under light polluted skies. Under such skies, I use the
same combo in my 8”, but can only make out the “shape” of the eagle with
averted vision. From darker skies, I tend to see what Stephen O’Meara sees, a
little kid under some white sheets with their hands sticking out to the sides.
This effect is more obvious when I screw in my UHC filter. From light polluted
skies, for most part all I can make out is some misshapen fuzz surrounding the
star cluster without a UHC type filter.
Summer is also an excellent time to view globular clusters,
and there are heaps of them abound since the center of our galaxy is in full
display. The best part about globular clusters is that they all have individual
characters, provided you have enough aperture to break them up. The minimum aperture
required for a good view of globulars in my opinion is a scope 6” and larger.
At this aperture you start to resolve some of the smaller globs, as well as
fully resolve some of the bigger and brighter ones. The best globulars, in my
opinion are M4 in Scorpius, M22 and M55 in Sagittarius , M13 in Hercules and M5
in Serpens. I chose these five as they are easy to resolve in scopes as small
as 76mm.
M4 is known as the cat’s eye globular for a reason. There is
a small bar of stars crossing the width of the globular that is readily
resolvable in small scopes. This globular has the most character in small
scopes (well there are other’s that are nice, but they are mostly southern
globulars and are not visible from northern latitudes) since it has that unique
feature. Also the overall branch magnitude of its constituent stars are higher,
making it more resolvable.
Seeing how I moved from the southern hemisphere, I refer to
M22 and M55 as poor man’s Omega Centauri. Now I am sure you have all heard of
Omega Centauri and how brilliant and resolvable this huge southern globular is.
M22 and M55 are close in visual appearance. Both are fairly loose globulars,
appearing more like open clusters at very high magnification in larger scopes.
M22 also appears oval in shape, much like its larger cousin due to its fast
rotational speed. Both globulars are a joy from dark skies, even in scopes as
small as 76mm. I see good resolution in both. But for a good view I would
suggest using at least a 130mm scope.
M13 in Hercules is a weird one. Hailed the best of the
north, and yet not the best in my humble opinion. I reserve that throne for M5
in Serpens (that is discounting M22 since atmospheric extinction removes that
splendor for most of the folks living further north). M13 has a tight core,
similar to 47 Tucana in the south (although I feel M5 is more the poor man’s 47
Tuc not M13!). There is very little resolution (well there is at the periphery)
in small scopes (76mm-114mm). The globular only starts to get interesting, and
at magnifications about 100x I might add in scopes 6” and larger. In those
scopes, you get resolution down to the blurry core (although for the best and
most consistent views, you need at least an 8” scope). In the 8” scope, I can
make out the propeller effect in the globular. In this regard, M5 is better,
showing more resolution in the smaller scopes than M13.
And there you have it, the summers best all wrapped up in a
single blog entry. I hope to do more visual observing in the coming months, at
least until Orion and friends show up early winter to revisit some of my
imaging targets. Till then enjoy.