The Caldwell Objects

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High-resolution blue-light images show the
reflection nebulosity as a vast network of filaments.
These features show a continuum spectrum
believed to be caused primarily by starlight
scattering off dust, and it is this reflection
nebulosity that we can spy visually through our
telescopes. Red-light images, however, show
waves of ionized gas lined with splotches of dust
that seem to be rippling away from the star in
several directions. The long southern extension
stands out in red light and is composed of faint
parallel streamers, the easternmost of which has a
relatively sharp outer edge. In the view of the late
Robert Burnham Jr. "the appearance seems to
suggest that this boundary is the edge of a zone
which has been swept clear of nebulosity by the
northward motion of the star." This motion might
also explain the apparent "rippling" of gas ahead
of the star in its present position. If the distance of
1,600 light-years is accepted for AE Aurigae, the
cloud of reflective material extends at least 9
light-years from the star.
AE Aurigae is visible with the naked eye just
northwest of an obvious tight, "hazy" grouping of
suns, the brightest of which are 5th-magni-tude
16,19, and IQ Aurigae. AE Aurigae and its
neighboring asterism, which Sky & Telescope's
Alan M. MacRobert likens to a "leaping minnow,"
lie outside a divine, well-defined brush stroke of
Milky Way. When I train my 10x50
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binoculars to that part of the sky, I'm surprised to
find the magnitude-7.5 open cluster NGC 1893
(about 1° southeast of the "minnow") pulling my
attention away from AE Aurigae and the nakedeye
asterism. The reason for this is obvious. To
the naked eye the asterism looks fuzzy, so
curiosity causes me to raise my binoculars to it.
Once I find the field in my binoculars, the
asterism is no longer fuzzy, but nearby NGC 1893
is, and curiosity takes control once again. (The
diffuse emission nebula interwoven with NGC
1893 in the photograph on page 122 is IC410.)
Little has been published about IC 405's
visual appearance. Burnham discusses only its
physical and photographic qualities. The most
descriptive discussion known to me appears in
MacRobert's book Star-Hopping for Backyard
Astronomers. There he writes, "In moderately
large amateur telescopes the 'flames' appear as a
large vague glow toward the star's east and north
about 20' across. To my surprise, [my] 6-inch
seemed to show hints of it despite the light
pollution. Quite a catch!" Roger Clark lists IC
405's apparent magnitude as 10.0 in his Visual
Astronomy of the Deep Sky, and he suggests that
relatively low powers (20x for a 6-inch telescope
and 41x for a 12-inch) are best for viewing it. I
found it to shine at magnitude 9.2 in the 4-inch at
23x; this magnitude applies to the reflection
nebula, described by MacRobert, that lies
immediately east and north of AE Aurigae.
Given its diffuse nature, IC 405 would seem
to be a visual challenge, but it isn't. Most
surprisingly, from Hawaii the object reveals itself
in 10x50 binoculars as a faint puff of vapors
southeast of AE Aurigae; averted vision is
required, however. In the 4-inch at 23x the glow
breaks down into finer details, but this requires
intermittent viewing over a period of at least an
hour. I find it helpful to gently
Deep-Sky Companions: The Caldwell Objects