The Caldwell Objects

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NGC 4889 appears elongated northwest to
southeast. Under excellent seeing conditions its
"extensions" break away from the main body and
stand alone as two independent fuzzy spots:
NGC 4886, a compact 13.9-magnitude galaxy to
the northwest, and NGC 4898AB, a magnitude-
13.6 pair of tightly interacting galaxies. I sketched
these companions without knowing of their
existence, believing at first that they were
perhaps part of a linear bar belonging to NGC
4889. This observation demonstrates the human
eye's ability to plumb the universe's depths with
a small telescope. It also shows that compact
13th-magnitude galaxies can be seen through
small telescopes under dark skies. The fact that
any of the Coma Cluster's galaxies can be spotted
from Earth in a 4-inch telescope implies that they
are quite sizable. Indeed, NGC 4889 is immense.
At its estimated distance of 300 million lightyears
its 2.8'-wide
35
body measures 240,000 light-years — about 2½
times the size of our own Milky Way. By dint of
the universe's expansion, NGC 4889 whisks away
from us at an astounding 6,500 km per second.
Of course, viewing the Coma Cluster
through larger instruments is mind-boggling.
Texas amateur Barbara Wilson used a 13.1-inch
f/4.5 reflector at 166x to see the entire field centered
on NGC 4889 and NGC 4874 "full of faint
nebulous round objects at the limit of vision." She
saw dozens more when she moved the telescope
one field-of-view diameter to the northeast. She
ended her commentary with a single word:
"Fascinating!" The Coma Cluster is indeed a vast
jungle of galaxies, for some 30,000 of them can be
spied within 6° of the cluster's core down to
magnitude 19.0 — posing an imaging challenge
to any amateur who owns a moderate-sized
telescope and a CCD camera and who wants to
explore this celestial heart of darkness.
Deep-Sky Companions: The Caldwell Objects