The Caldwell Objects

10
a powerful hold on observers. Like
magnets, they immediately attract our
gaze, pulling it away from nearby
objects that might be equally interesting.
So unless an observer feels
adventurous, he or she will probably
not seek out NGC 663 in lieu of M103
without reason (like this suggestion
that you do so). I've been guilty of this
oversight myself.
NGC 663, as it turns out, is a
wonderful object, being at least 0.3
magnitude (32 percent) brighter, 1,000
light-years closer, and 2½ times larger
than Μ103. The cluster's 108 measured
members (roughly 8th magnitude and
fainter) fill an area of sky measuring
¼°, or 31 light-years,
across. By comparison, M103 packs some 172
suns in an area of sky only 6' across, which, at its
distance of 8,100 light-years, is equal to 14 lightyears
of space. (This high concentration of stars
in such a small area of sky is, of course, why
Μ103 packs such a visual punch.)
From a dark sky NGC 663 can be seen with
the naked eye, but you have to take the time to
resolve it from the two roughly 6.5-magnitude
stars about ½° west and south-southwest of it.
While comparing the apparent brightnesses of
these three objects, I realized that NGC 663's
listed magnitude (7.1) is too faint. Using 7x35
binoculars, I estimated the cluster's apparent
visual magnitude to be 6.7. Barbara Wilson
independently deduced a value of 6.5. So NGC
663 is arguably at least half a magnitude brighter
than commonly believed. (Wilson also wonders
why William Herschel's description in his
original Philosophical Transactions catalog differs
from that in the General Catalogue, since John
Herschel did not observe the cluster and William
did so only once.)
Viewed with the 4-inch at 23x the nearly 3° field
centered on NGC 663 comes alive with clusters,
double stars, patches of Milky Way, and streams
of dark nebulosity. NGC 663 itself is immediately
very well resolved. In fact, several of its brightest
(8th-magnitude) members can be glimpsed in
7x35 binoculars. My visual impression with the 4inch
is one of an elliptical orb with snaking
chains of 8th- and 9th-magnitude stars, all of
which are projected against a lens-shaped
backdrop of fainter suns. Similarly, Jere
Kahanpää (Jyväskylä, Finland) used a 6-inch
refractor at 52x to see a "beautiful cluster" with its
major axis oriented east-west. In the Genesis at
23x the star chains radiating from the cluster's
core seem to gravitate to the south; one especially
long arm ends in a bright pair of stars that all but
pinches NGC 659 ½° to the southwest.
At 72x the cluster's core is fragmentary,
being composed of three stellar groupings
shaped somewhat like a horseshoe. The horseshoe
asterism is the result of a prominent northsouth-trending
dark lane that rips through the
50 Deep-Sky Companions: The Caldwell Objects