The Caldwell Objects

172
42
nent knot of stars lies to the south of the core. The
cluster is situated in a rich Milky Way field, so it
is hard to discern which stars belong to the
cluster and which to our galaxy's populous disk.
Of course, with a really big telescope NGC
7006 reveals itself in ways that can only be
imagined by the owners of small instruments. In
September 1998, Brent Archinal and I observed
NGC 7006 with the 31-inch reflector at the
Warren Rupp Observatory in Mansfield, Ohio.
The cluster was a scintillating mass of dim
starlight. At high power we saw an unresolved,
starlike inner core surrounded by a dark ring that
defined the inner edge of a finely resolved,
though jagged, outer core. With averted vision
thin arms radiated out from the stellar "hole" like
the limbs of a starfish wrapped around a rock.
The outer halo appeared loose and fractured, as if
its shell were so old and brittle that pieces of it
were flaking off into space.
Large-telescope users might be interested in
this challenge: a tiny cluster of galaxies lies just 5'
to the southwest of NGC 7006. None of
these galaxies is plotted on the Millennium Star
Atlas, but a few of them can be seen in the
Digitized Sky Survey image on page 169.I believe
they will certainly fall to large Dobsonians.
Before leaving the area be sure to return to
Gamma Delphini, which is a beautiful double
star. The magnitude-5.2 secondary lies 9" to the
west of the yellowish primary; the stars were 12"
apart in 1823. Adm. William Henry Smyth saw
the secondary gleam with a "light emerald" hue.
The colors Smyth saw recall those of the famous
double star Albireo in the nose of Cygnus, the
Swan. Interestingly, though, the spectral types of
Gamma Delphini's components are K1IV
(primary) and F7V (secondary), respectively —
basically right next to each other on the
OBAFGKM sequence of stellar spectral types. So
any color contrast perceived by Smyth was
undoubtedly due to psychology, or intensity
threshold effects in the eye. I see two golden
stars, with the fainter one having a cooler (bluer)
hue. But the only important question is: what do
you see?
Deep-Sky Companions: The Caldwell Objects