The Caldwell Objects

(which does not appear on Sky Atlas 2000.0 but is
plotted in the Millennium Star Atlas and
Uranometria 2000.0) is commonly picked up
through telescopes with moderately large
apertures and mistaken for a comet. (NGC 4562
appears in the lower right-hand corner of the
photograph on page 150.) Another galaxy that
may be stumbled upon in the search for NGC
4565 is NGC 4494, a 10th-magnitude elliptical
galaxy about ½ ° east-southeast of 17 Comae
Berenices.
Perhaps the greatest visual challenge posed
by NGC 4565, though, is to sight the edge-on
spiral in 7x35 binoculars. Its thinness and its
prominent dust lane both cause the galaxy to be
close to the limit of detectability. I succeeded at
an altitude of 4,200 feet under very dark
Hawaiian skies. It was a very difficult observation,
requiring a lot of time and patience for me
to be confident I had seen the galaxy's slender
body. Sky & Telescope editor Joshua Roth saw it in
his 60-mm f/5.9 refractor from the Amateur
Telescope Makers of Boston's dark-sky site in
Westford, Massachusetts, and called it a
The Caldwell Objects
38
"sweet little needle of light."
Since NGC 4565 and its rival, NGC 891 in
Andromeda, lie at about the same altitude after
sunset (at opposite ends of the sky) around the
start of spring in the Northern Hemisphere, try
observing them both on the same night. The two
galaxies are essentially the same distance from
us, and are roughly the same size, but NGC 4565
is much more conspicuous because its surface
brightness is twice that of NGC 891. This
difference in surface brightness can be attributed
at least in part to extinction — the absorption and
scattering of starlight by intervening dust, which
lies in our Milky Way and within the edge-on
spirals. NGC 891 lies on a sightline that skirts our
home galaxy's midplane, and the passage
through our galaxy's dusty disk dims NGC 891's
light by 0.2 magnitude, or 17 percent. NGC 4565,
by contrast, is a mere 3½° west of the north
galactic pole — an essentially transparent
window onto extra-galactic space — and its light
is reduced by only 0.05 magnitude (5 percent).
Roth says he has yet to see NGC 891 in his 60-mm
telescope.
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