
Binocular Universe: Houston’s Triangle
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Binocular Universe:
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Sixty-nine years ago this month, the face of amateur astronomy changed forever. A seed was planted in September 1946 that would blossom into a decades-long infatuation with deep-sky observing among amateurs everywhere. Without any fanfare at the time, a man named Walter Scott Houston took over the reigns of a small column in Sky & Telescope magazine called Deep-Sky Wonders. Another prolific observer, Leland Copeland, originated the column and penned it for four years. But it was under Houston's watch that it evolved from a modest tabulation of three or four suggested objects into an engaging dialogue that would capture the imagination of readers for nearly half a century.
Above: Summer star map
from Star Watch by Phil Harrington.
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That first column written by Houston, a mere dozen lines
in length that belied this amazing man's tale-spinning nature, listed three objects
in the late summer sky -- M57, M27, and M11 -- that I like to think of as
Houston's Triangle. All three are visible through common binoculars, although
they present three different levels of difficulty.
Above: Finder chart for this month's Binocular Universe. Chart adapted from Touring the Universe through Binoculars Atlas
(TUBA) |
Of the three, M11, the famous Wild
Duck Cluster in Scutum, is the easiest to see through binoculars. To find it,
trace Aquila the Eagle's diamond-shaped body from Altair to the curve of its
tail-feather stars, Lambda and 12 Aquilae. Together with Eta Scuti, Lambda and
12 form a three-star arc that curves right toward M11. More than 1,000 stars
belong to this open cluster, making it the densest of its type among the
Messier objects and a real showpiece in telescopes. Through binoculars, M11
actually looks more like an unresolved globular cluster than an open cluster.
Except for a solitary 8th-magnitude point buried within, all of M11's suns
shine between 11th and 14th magnitude, too faint to be resolvable with common
binoculars (it's very doable if you have keen eyes and 20x binoculars).
Next comes M27, nicknamed the Dumbbell Nebula for its telescopic resemblance
to a weightlifter's barbell. Even the view through 10x50 binoculars begins to
reveal its unusual shape. M27 carries the distinction of being the first
planetary nebula ever discovered, by Messier himself in 1764, and only one of
four listed in his famous catalog. Located about 1,250 light years away, M27 is
one of the biggest and brightest planetary visible in northern skies.
While it is easy to tell M27 apart from the surrounding
stars through binoculars, locating it in the first place can be another matter.
That's because its home constellation, Vulpecula the Fox, is nearly impossible
to make out against the background Milky Way field. Rather than scratch your
head in frustration, do as most others do and start your search in neighboring
Sagitta the Arrow. Even though Sagitta is also very small, its four main stars
create a distinctive pattern that stands out more prominently. Concentrate your
aim on Gamma Sagittae, the star marking the Arrow's eastern tip. Look about
half a field due north of Gamma for a triangle of stars formed from 14, 16, and
17 Vulpeculae. M27 will look as a smudge of grayish light less than half a
degree southeast of 14 Vulpeculae, the easternmost star in the triangle. Even
7x binoculars will show the nebula's box-shaped glow floating in a field strewn
with stardust. Catching a hint of its hourglass form, however, will take more
magnification that most handheld binoculars can muster.
Lastly, we have M57, the Ring
Nebula in Lyra. M57 lies twice the distance from us as M27, and as a result,
appears much smaller. While M27 measures 8'x6' across, the Ring is just 1.4' x
1' in size. Even though M57 at magnitude 8.8 is bright enough to be visible
through most binoculars, it will look like nothing more than another faint
star.
The challenge to binocularists is to figure out which
faint star is actually the Ring Nebula, since its tiny donut-shaped disk needs
at least 25x to be resolved. Although that task sounds daunting at first, as
luck would have it, the field surrounding M57 actually simplifies the task.
Center your aim along the bottom of Lyra the Lyre's rectangular frame, halfway
between the star Sulafat (Gamma Lyrae) marking the eastern corner and Sheliak
(Beta Lyrae) at the western corner. M57 is found almost exactly halfway between
the two. To confirm that you are looking in the right place, M57 is the last
point in a diagonal line of five faint stars that starts just north of Sheliak
(Beta). If you can see all four real stars in that line as well as a slightly
fuzzy point just beyond, then you've hit M57.
There are plenty of targets within Houston’s Triangle.
Let’s revisit some old favorites, as well as stop by others for the first time.
For instance, if you scan from M27 to M57, you’ll pass the
star Albireo, which marks the beak of Cygnus the Swan. Albireo is a
showpiece double star through small telescopes, with a 3rd-magnitude golden
primary star accompanied by a 5th-magnitude sapphire-blue companion. Although
their colors aren’t as apparent through binoculars, both stars can be spotted
through steadily held 10x50s.
Continuing past Albireo, you will also pass the globular
cluster M56. Charles Messier himself discovered this distant swarm of
100,000 or so stars on January 19, 1779. M56 is nestled among a well-populated
field of stars, southeast of a conspicuous asterism of stars shaped like the
number 7. Binoculars show M56 as a fuzzy 8th-magnitude glow punctuated by a
brighter core, a view reminiscent of Messier’s own. He described it as a
"nebula without stars, having little light.”
Of all the deep-sky targets within the triangle, the
brightest by far is the Coathanger asterism. Also known historically as Brocchi’s Cluster (even
though its non-cluster nature is well established) and Collinder 399, the
Coathanger stands out nicely through any pair of binoculars. It’s always well
worth a revisit. The outline is drawn from six stars aligned in a straight line
that marks the Coathanger's cross bar, and another four that curve away to
create the hook.
Since we are discussing Walter Scott Houston this month,
it’s appropriate that the Coathanger be included. Scotty first introduced the
Coathanger to me, and likely countless others, thanks to a small write-up in an
old newsprint star atlas he created more than half a century ago.
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From M27, look 2° due west to 5th-magnitude 12 Vulpeculae.
Can you spot a faint glow just to the north? That’s the open cluster NGC 6830. Some two dozen stars call this cluster home. My 10x50
binoculars only show the faintest hint of the cluster. It’s much more obvious
my 16x70s; in fact, I can even spot a few of its brightest stars, but only with
averted vision.
Finally, we have Stock 1.
This is one of those objects that usually goes unnoticed because it covers such
a wide field. Spanning 1 degree across, only 19 stars actually populate the
group. But the area contains many others that appear to belong by chance
line-of-sight. Stock 1 spans 52' across, but these imposters cause the cluster
to appear half again larger. Stock 1 is about 3.5 degrees southeast of Albireo
and 2 degrees east-northeast of Alpha Vulpeculae. Look for a distinctive,
though faint, trapezoid of four 7th- and 8th-magnitude stars toward the group's
eastern edge. These suns are centrally located within the cluster. The
cluster's brightest true member is 7th-magnitude HD 184928, northwest of the
trapezoid. A 6.5-magnitude star looks to be the brightest, but is not a true
affiliate.
Until we get together again next month, I hope that
you get many opportunities to enjoy the beauty of the late summer sky. And
always remember that two eyes are better than one.
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About the Author: Looking for more targets to enjoy through your binoculars? Read Phil's article Tour 10 Fall Binocular Treats in the August 2015 issue of Astronomy magazine. |
- okiestarman56 likes this
4 Comments
another great guide for binocular users! thanks so much Phil!
Ditto.
Here's a photo of Houston Hollow that I took last month at Stellafane.
Attached Thumbnails
Dave,
Thanks for sharing the photo. For years Scotty's column was the first thing I tuned to in Sky and Telescope. It's so hard to believe his passing was over 21 years ago, and that he'd be 103 if he were still with us.
Thanks Phil, for keeping his memory going.
John O'Hara
I love Binos but my neck hates them