Sky and Telescope - July 2017 - 45
Under the Stars by Fred Schaaf
Enter the Summer Citadel
The sights and scents of the season encourage a visit to an old friend.
KURIOUSG EORG E / WIKIMEDIA COMMONS / CC BY-SA 3.0
he greatest science popularizer of
the past 50 years - and probably of
all time - was American astronomer
Carl Sagan. Among his many quotable
statements, the most famous has always
been, "We're made of star stuff."
But more than a century before Sagan
said those words, American poet Walt
Whitman said something similar. "I
believe a leaf of grass," Whitman wrote,
"is no less than the journey-work of the
stars." Of course, Whitman couldn't
have known, as Sagan did and meant to
convey, that the creation of life on Earth
was literally a work of the stars. Carbon,
oxygen, and other essential elements in
our composition, and substances that
went into the formation of our Sun (a
third-generation star) and its planetary
system, came from the supernovae of
earlier generations of stars.
Whitman lived in a time before anyone knew anything about nucleosynthesis. But as I stand on a fragrant, freshly
mown lawn while a July dusk ever so
slowly deepens, and Vega and Arcturus
roll into view followed by dozens and
then hundreds more stars, I can't help
but think of Whitman's beautiful and
seemingly prescient line. I'm freshly
stirred to seek out the stellar wonders of
a summer night.
Summer's citadel of stars. There's
much to be said for tracking down
sights you've never seen before, but on
a calm summer night you should also
return to the traditional objects on
everyone's watch list. For instance, take
the time to consider a masterwork made
by the stars, fashioned by its component
stars with gravity and nuclear fusion.
It's the best placed and most popular
of all globular clusters for observers at
mid-northern latitudes and may even be
the most popular deep-sky object of any
kind except for winter's M42, the Great
Orion Nebula. But unlike M42, this
summer cluster passes nearly overhead
as seen from the world's most populous
latitudes (exactly overhead from 36½°
N). I'm speaking, of course, about M13,
the Great Globular Cluster in Hercules.
Sagan at least once used the phrase
"the citadel of the stars" in his Cosmos
series, and if he didn't sometimes apply
the phrase to globular clusters, somebody should. It's an apt description of
these congregations of up to hundreds
of thousands of stars seemingly guarding the rest of our galaxy.
You can see quite a few of M13's
stars in a sizable telescope. But your ﬁrst
approach to M13 should be with the
naked eye. You can see it as a soft little
hazy patch of light on the west side of
the Keystone asterism in Hercules -
under skies with a limiting magnitude
of about 6.0 or better. Binoculars reveal
it in more light-polluted areas, showing
a larger puff of light ﬂanked by 7thmagnitude stars on either side.
Stellar stronghold revealed.
Through an 8-inch, 10-inch, or larger
telescope M13 truly looks like a mighty
fortress of stars. It has more obvi-
ous arms or tentacles of stars - John
Herschel's "curvilinear branches" -
extending outward from it than perhaps
any major globular. Just let the wonder
ﬂow through you for a while as you
behold this beauteous, many-armed
beast - then you can search for its
subtleties. These include dark lanes: A
famous dark Y or propeller is centered
southeast of the cluster's core, but a
particular combination of aperture and
magniﬁcation helps make it more obvious (see page 55).
Also worthy of note in an 8-inch or
larger telescope is the 11th-magnitude
spiral galaxy NGC 6207, approximately
40 arcminutes northeast of M13. M13
is only about 23,000 light-years from
Earth, but NGC 6207 lies about 46 million light-years distant.
Happy 303rd, M13! M13 was discovered by the great Edmond Halley in
1714, the 58th year of his 85-year-long
life. That's 303 years ago.
¢ Contributing Editor FRED SCHAAF
has been writing about the skies above
us for more than 40 years.
s k y a n d t e l e s c o p e .c o m
* J U LY 2 017