Sky & Telescope - June 2024 - 59

SKY & TELESCOPE ARCHIVES
at the young age of 56. He taught at the
University of California Los Angeles and
at a summer school in Ojai, California,
and he also mentored amateur and
professional astronomers researching
galaxy clusters and the large-scale
structure of the universe. Abell's most
celebrated student may have been Ed
Krupp, the director of Griffith Observatory
in Los Angeles since 1974, where he
continues to inspire generations.
Although I never got the chance to
meet Abell, galaxies have held a fascination
for me since I first started using a
telescope in the 1980s. Each galaxy's
beauty and subtle variations reflect its
history, environment, and interactions.
The unseen, attractive hand of dark
matter affects membership of groups
and clusters, shaping their courses in
ways we are still discovering. Knowledge
about our targets enhances our experience
when viewing them in a telescope.
Let's dip into Abell's catalogs and take a
look at several clusters, some of whose
light has been traveling since the time
of Earth's formation.
Faraway Clusters
The nearest cluster to Earth - at a
distance of approximately 54 million
light-years - is the Virgo Cluster, which
is anchored by the giant elliptical galaxy
M87. However, Abell didn't include it in
his catalog as it's too spread out. Somewhat
farther out, at a distance of 340
million light-years, Abell 1656, or the
Coma Cluster, is the nearest rich cluster
in the catalog. (Clusters are classified as
rich or poor depending on the number
of galaxies they contain.) The Coma
Cluster, with its proximity and density
of objects, is the best galactic hunting
ground for amateur telescopes, with a
population estimated at perhaps up to
3,000 galaxies. The core of the cluster
lies 22
/3° west of 4.3-magnitude Beta (β)
Comae Berenices.
I have a project underway to view
galaxies in the cluster's central square
degree - so far I've detected about 700
galaxies within two-thirds of that area.
My 32-inch reflector allows me to see
as faint as magnitude 20, and I estimate
more than 1,000 galaxies will be
κ
visible in that central
square degree. The
whole cluster spans
25 square degrees in
the sky. To search it
at this level of detail
would entail more
than 1,000 hours of
eyepiece time - and
yield many more
galaxies. (Based on
my examinations of a
POSS plate, I estimate
there may be as many as 5,000 galaxies
in the area!)
Abell 2065, the Corona Borealis
Cluster, has long been held as a benchmark
for visual observers. The distance
to Abell 2065 is a little less than one
billion light-years, and its brightest
galaxies are at 16th magnitude. The
cluster lies 1¾° southwest of 3.7-magnitude
Beta Coronae Borealis.
The classic series of the Webb Society
Deep-Sky Observer's Handbook from the
1970s to 1980s included in its volume
on clusters of galaxies, the fifth in
the series, Ron Buta's (University of
Alabama) description of Abell 2065 as
seen through the 36-inch reflector at
McDonald Observatory. Buta described
the group as " very difficult " and, except
for the " three brightest members, the
cluster was a challenge. " Few amateurs
in 1982 had access to a 36-inch telescope,
but about 10 years later I was able
to purchase a 25-inch reflector and start
hunting for some of these challenging
β
γ
CrB
β
γ α
SERPENS
CAPUT
ι
15h
Arcturus
α 14h
M53
α 13h
CLUSTERING OF CLUSTERS A handful of Abell objects populate three adjacent constellations.
On late spring nights you can " cluster-hop " among them.
sk yand tele scope .o r g * JUNE 2024 59
δ
Abell 1963
Abell 1958
Abell 1961
Abell 2065
ε
BOÖTES
ρ
M3
CLUSTER COLLECTOR
George Ogden Abell
only lived to 56 years old,
but he left behind a rich
legacy. Although best
known for his monumental
work on galaxy clusters,
he also turned his attention
to other objects, such
as planetary nebulae.
objects. Experienced
amateurs Barbara
Wilson and Larry
Mitchell included
Abell 2065 on their infamous AINTNO
(the Association of Invisible Nebulae
and Things Nobody Observes) list - to
win the AINTNO award, an observer
would have to snag 45 of the cluster's
galaxies. In 2004 I spent four and a half
hours over two nights hand-guiding
my scope, and I observed 51 galaxies in
Abell 2065. This was the most technically
challenging viewing I have done
thus far, as the high-power fields of
many galaxies lacked reference stars.
But this is just the beginning of our
explorations, as it's one of the nearest
galaxy clusters. For those with an
everlasting itch to explore the deepest
reaches of space, we can go farther
afield. The " moderate distance " objects
are represented by a group of three
clusters: Abell 1958, Abell 1961, and
Abell 1963, all around 2.8 billion lightyears
away. They're very close to each
other in the sky, lying only about 15′ to
20′ from one another in central Boötes
- all three fit into the same wide-field
0 1 2 3 4 5 6 7
Star magnitudes
α
CANES
VENATICI
+30°
γ
Abell 1656
β
COMA
BER
M64
+20°

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Sky & Telescope - June 2024

Table of Contents for the Digital Edition of Sky & Telescope - June 2024