56 ASTRONOMY • JANUARY 2022
83 M22
In 1665, while observing Saturn (which was located in Sagittarius at the time), German
astronomer Johann Abraham Ihle came upon an unexpected sight. Just over 2° north-
east of 3rd-magnitude Kaus Borealis (Lambda [λ] Sagittarii) at the top of the Teapot
asterism, he found a small, nebulous patch. Although he had no idea what he had seen,
Ihle had unintentionally discovered the first globular cluster. Today, we know it as M22.
The Hercules Cluster (M13; see #69) may be considered one of the finest globular
clusters in the night sky, but it gets stiff competition from M22, which appears larger
and a half-magnitude brighter than its Herculean counterpart. That apparent supe-
riority, however, is an illusion caused by disparate distances. M22 is little more than
10,000 light-years away — less than half the distance to M13.
Despite M22 containing less than half the stars of M13, it still proves easier to resolve.
A 3.5-inch scope is all it takes to spot at least some stars around the fringes. An 8-inch is
more than enough to display a multitude of faint stars strewn across the entire cluster.
Make a slow, careful study of M22, noting its overall shape. Most globular clusters are
round, but not M22. It’s elliptical, with the long dimension angled northeast-southwest.
This odd shape is apparent through nearly all scopes and even in larger binoculars.
Of the 150 known globular clusters associated with the Milky Way, M22 is one of only
four that contains a planetary nebula. In 1985, NASA’s Infrared Astronomical Satellite
uncovered a mysterious infrared source among the cluster’s stars. After four years of
research, astronomers showed that the source was a planetary nebula located 1' south
of the cluster’s center.
Finding this planetary, known as GJJC 1, takes an aperture of at least 20 inches. The
best seeing conditions are also a must, because at least 600x is required to make out
the planetary's tiny disk. — P. H.Located in Serpens Caput, a constel-
lation with few deep-sky objects,
Seyfert’s Sextet was one of the first
compact galaxy groups ever noted.
That occurred in 1948, when astrono-
mer Carl Seyfert discovered that the
previously cataloged NGC 6027 was
actually more than one object. His
Sextet became the densest group of
galaxies known at the time.
Seyfert’s initial observation
described six galaxies close together,DAN CROWSONDON GOLDMANThe four physically associated
members are galactic Lilliputians.
Astronomers believe the entire
group would fit inside the width
of the Milky Way, some 100,000
light-years. Three share a common
halo that in most galactic collisions
would generate new star formation,
but not here. Perhaps this means
that within the next several billion
years, the galaxies might merge
and form a large elliptical galaxy.
Edouard Stephan discovered
NGC 6027 in 1882, but didn’t
resolve the others. This highly
inclined barred lenticular galaxy
is the group’s brightest member
at magnitude 14.7. NGC 6027a is
magnitude 14.9. Perhaps the dark
lane of this Sa peculiar spiral dims
it a little. It’s a tiny version of the
Sombrero Galaxy (M104; see #29).
NGC 6027b is similar in size and
nature to NGC 6027 but is a more
challenging magnitude 15.3.
NGC 6027c is by far the group’s
faintest member at magnitude 16.7.
It’s a highly inclined SBc or SBd
galaxy. Hubble photos show it is
rich in young blue stars but poor in
HII regions. Beyond the true group,
NGC 6027d is a giant face-on
barred spiral more than 800 million
light-years away. At magnitude 16.5,
it’s a challenge.
Observing Seyfert’s Sextet
requires a large telescope. You
might glimpse it in a 13-inch
telescope under excellent skies,
but resolving members requires
more aperture, magnification, and
a very steady atmosphere. — A.G.84 Seyfert's Sextet
but that isn’t the case. Later observa-
tions revealed only four interacting
galaxies (NGC 6027 and NGC 6027a,
b, and c) at a distance of 190 million
light-years. A fifth galaxy, NGC 6027d,
is actually 410 million light-years
behind the group. And the sixth gal-
axy isn’t a galaxy at all — it’s a plume
of stars generated by interactions
between NGC 6027 and NGC 6027a.
The galaxies have diameters that
range from 0.9' to 0.2'.