Sky and Telescope - June 2015 - 64

Corona Borealis Challenge

Abell 2065 in Corona Borealis
Object
PGC 54880

Type
Galaxy

Magnitude
17.3

Size/Sep.

Dec.

0.2′

15h 22.5m

+27° 43′

22.5m

+27° 43′

MCG +05-36-022

Galaxy

15.7

0.4′

15h

PGC 54883

Galaxy

15.4

0.4′

15h 22.5m

+27° 42′

PGC 54876

Galaxy

15.4

0.4′

15h 22.4m

+27° 43′

MAC 1522+2741G

Galaxy

17.5

0.2′

15h 22.6m

+27° 41′

22.7m

+27° 40′

PGC 54890

Galaxy

16.7

0.3′ × 0.1′

15h

PGC 54891

Galaxy

15.7

0.3′ × 0.2′

15h 22.6m

+27° 41′

PGC 54894

Galaxy

16.4

0.2′

15h 22.7m

+27° 37′

SDSS J152245.11+273650.7

Galaxy

17.3

15h 22.7m

+27° 37′

22.3m

+27° 48′

PGC 54868
SDSS J152215.40+274657.0
MAC 1522+2745B
TYC 2031-874-1
TYC 2031-972-1

Galaxy

16.0

0.3′

15h

Star?

17.8

15h 22.3m

+27° 47′

Galaxy

17.6

0.2′

15h 22.6m

+27° 45′

Star

10.7

15h 22.6m

+27° 46′

15h

+27° 43′

Star

11.6

22.3m

Angular sizes and separations are from recent catalogs. Visually, an object's size is often smaller than the cataloged value and varies
according to the aperture and magniﬁcation of the viewing instrument. Right ascension and declination are for equinox 2000.0.

Placing each star just outside the ﬁeld of view made
these observations possible. This was easier to do with a
narrow ﬁeld of view eyepiece.
Showing how eﬀective this technique can be, the
faintest galaxy I've seen so far in the entire cluster is
MAC 1522+2745B (magnitude 17.6) which is right
next to the brightest foreground star, TYC 2031-874-1
(magnitude 10.7). The galaxies appearing closest to the
star TYC 2031-972-1 (magnitude 11.6) present similar
diﬃculties. However you approach them, be prepared for
an observing challenge.

Where's the Edge?
A deep, wide-ﬁeld image centered on 2065 shows galaxies well beyond the obvious central concentration. So
where's the edge of the cluster? There's no deﬁnitive
answer, partly because 2065 is part of the Corona Borealis Super Cluster, a group of eight Abell galaxy clusters
that are gravitationally bound and apparently in the
process of condensing into a single super-duper galaxy
cluster. In addition, there are non-related galaxy clusters
near 2065 on the plane of the sky, making this a crowded
area for faint galaxies. For the purposes of my observations I considered 2065 as being roughly 30 arcminutes
in diameter - the apparent size of the Moon - because
the cluster seems approximately this big visually.
64

June 2015 sky & telescope

Thoughts
Although the implication is there, published observations of 2065 usually don't mention the galaxy cluster's
beauty and wonder. It takes intellect, imagination, and
skill - common traits among visual observers - to see
the beauty of something that's barely perceptible to the
eye. The resulting wonder that can be mined from such
an observation is an important aspect of astronomy and
our humanity.
Without the research done by generations of dedicated astronomers, 2065 would only be a meaningless
collection of small, faint smudges. Thanks to their work,
we know that each of these smudges is a tremendous
galaxy, that each galaxy is over a billion light-years away,
all are gravitationally bound to each other, and 2065 will
eventually form a single galaxy supercluster with seven
other clusters. Wow.
One of the exquisite pleasures of visual astronomy
is the contemplation of this knowledge while observing
just one of AGC 2065's faint galaxies with your own telescope. Creating a personal connection with this stupendously distant part of the universe is just that easy, and
just that diﬃcult. ✦
Howard Banich will be observing brighter objects for a while
now, and invites e-mail at howard.banich@nike.com.

Sky and Telescope - June 2015

Table of Contents for the Digital Edition of Sky and Telescope - June 2015