The Caldwell Objects

63
to the scrutiny of amateur telescopes? My 4-inch
seems to perform just fine on it at 23x. The first
impression I got was that of a ghastly, pale ring
of ashen light trapped within a triangle of 10.0- to
11.5-magnitude stars. The northwestern and
southwestern stars each have a roughly 12.5magnitude
companion separated by some 3'. (The
brighter member of the southwestern pair is a
fine double star in its own
right, though it is best seen at higher magnification.)
The triangle's third star lies just to the
east of the nebula and shines at about magnitude
11.5, though it looks much fainter in photographs.
With averted vision, the Helix's edges
appear sharply defined. The northwestern side
looks thinner than the southeastern side. Look for
two enhancements in the luminous ring; one, to
the northeast, connects to another, to the
southwest. Try averted vision and see if these
enhancements don't look like a pair of ghostly
lips blowing you a kiss. With time, they appear
mottled. The central cavity is quite transparent at
low power.
With a lot of patience you can see a fair
amount of detail in the nebula at 72x (the object
all but disappears with anything much
252
higher). First, I suggest you draw the surrounding
star field before you go out; use the
photograph below as a guide. That way you can
pencil in nebular details without having to worry
about getting the stars right; you can later tweak
the sizes of the stars to reflect their relative
brightnesses in the eyepiece. Now, working your
way from the inside out, first check the "hole" for
the magnitude-13.4 central star. It takes time for
me to see it with my 4-inch, but there's no
mistaking it once I do. If you have a sturdy
mount, try looking for the central star with a
higher magnification, say 140x. You will not see
the nebulosity, but that's not what you're after at
this point.
Next look for the dense inner ring with 72x;
it's the brightest part of the entire nebula. The
ring contains several background stars and
nebulous enhancements, especially to the
northwest and southwest. To see the outermost
nebulosity, try placing the Helix outside your
field of view, then slowly bringing it back (the
eye is more sensitive to light in motion). The
nebula's broad eastern portion has a dim but
sharp edge that is not difficult to spot in this way.
The most challenging part of the nebula lies to
the west, where a tail of gas appears to curve
northward from the southern rim of the inner
annulus. This tail meets the 10th-magnitude star
bordering the nebula to the northwest, then
curves back to the inner ring and connects with
its northern edge. This last wisp of gas is the most
difficult portion to see, but if you can trace it you
will have mapped the Helix's full "double twist."
If you fail to see this dim wisp, return to low
power and look again. Low power will condense
its light and make it more apparent. Do not
expect to see all this detail at once with a 4-inch.
My drawing at upper left is a composite of the
Helix as seen at low, medium, and high power.
I have a special challenge for the owner of
Deep-Sky Companions: The Caldwell Objects