Fred Schaaf
OBSERVING
Northern Hemisphere’s Sky
Fred Schaaf welcomes your
comments at [email protected].The Fabulous Five
The globular clusters of summer are amazing to view.
M3 and M5. Glorious as it is, not everyone thinks M13
is the most splendid globular cluster north of the celestial
equator. Its competitors are M3 in Canes Venatici and M5
in Serpens. M3 has no even moderately bright stars nearby
to use as guides — so look for it about halfway along the
long line between Cor Caroli (Alpha Canum Venaticorum)
and Arcturus. M5 shines just 20′ from the golden 5th-
magnitude star 5 Serpentis and may appear almost a half
degree wide to viewers with 10-inch telescopes.
M22 and M4. M22 and M4 are low in the sky for
observers at mid-northern latitudes, so haze often dulls
their grandeur. But M22 takes your breath away on a truly
transparent dark night. It is signifi cantly brighter and
bigger than M13 and, being closer to us, has more indi-
vidually resolvable stars. M22 also lies just 2½°° northeast
of Lambda Sagittarii, the star that marks the top of the
Teapot of Sagittarius. And M22 is less than 1° south of the
ecliptic, so it receives frequent visits from planets.
M4, which glows just 1½° west of Antares, is fainter
than M22, M5, and M13. But it’s one of the three closest
globular clusters, so its stars are especially easy to resolve.
A large amateur telescope reveals M4’s full majesty, includ-
ing a multitude of individual pinpricks of light and a pecu-
liar bar of stars stretching across it from north to south. ✦It has always seemed to the author of this book that J. R. R.
Tolkien, in his delightful fantasy The Hobbit, unwittingly
created an exquisite description of M22 when he spoke of the
fabulous jewel called “The Arkenstone of Thrain”: “It was
as if a globe had been fi lled with moonlight and hung before
them in a net woven of the glint of frosty stars.”
— Robert Burnham, Jr.,
Burnham’s Celestial Handbook
The summer sky is where you’ll fi nd M22 — and almost
all the other bright globular star clusters visible from the
Northern Hemisphere. Space is short here, so we’ll tour
just a few of these globular clusters. Let’s concentrate on
what we might call the Fabulous Five.
Prepare for the Fabulous Five. Our galaxy’s globular
clusters form a vast spherical halo centered on the galactic
core, which lies in the summer constellation Sagittarius.
So we see most globulars in the span of sky that stretches
from M3, in the late spring constellation Canes Venatici,
to M2 and M15 in the early autumn constellations Aquar-
ius and (westernmost) Pegasus.
Only the brightest globular clusters are visible to the
naked eye, and even those are mostly borderline-visible
blurs seen with averted vision in dark skies. But it doesn’t
take a very large telescope to start transforming these
fuzzy glows into the celestial showpieces they really are.
Famous M13. For many amateur telescopic observers,
summer is virtually synonymous with M13. This cluster
passes almost overhead at 40° north latitude and is easily
found with binoculars and fi nderscopes along the western
side of the Keystone asterism of Hercules. Look for the
Keystone about^2 / 3 of the way between spring’s bright-
est star, Arcturus, and summer’s brightest, Vega. Once
there, you’ll see the fuzzy spot of M13, fl anked by two
lesser stars, about^1 / 3 of the way between Eta Herculis (the
northwest corner of the Keystone) and Zeta Herculis (the
southwest corner). If your skies are dark and M13 is high,
you will probably be able to see it with your unaided eyes;
some observers estimate it as bright as magnitude 5.3.
But it takes a 6- to 10-inch telescope to resolve large
numbers of stars in M13, making the cluster jaw-drop-
pingly magnifi cent. Note the long strands or arms of stars
that seem to radiate out from M13 more than from almost
any other globular cluster. While in Hercules, compare
M13 to the smaller but diff erently impressive M92.
DOUG MATTHEWS / ADAM BLOCK / NOAO / AURA / NSFSkyandTelescope.com July 2014 47Messier 22 is a swarm of multicolored stars when viewed through
a large telescope at high magnifi cation.