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The Caldwell Objects

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31<br />

High-resolution blue-light images show the<br />

reflection nebulosity as a vast network of filaments.<br />

<strong>The</strong>se features show a continuum spectrum<br />

believed to be caused primarily by starlight<br />

scattering off dust, and it is this reflection<br />

nebulosity that we can spy visually through our<br />

telescopes. Red-light images, however, show<br />

waves of ionized gas lined with splotches of dust<br />

that seem to be rippling away from the star in<br />

several directions. <strong>The</strong> long southern extension<br />

stands out in red light and is composed of faint<br />

parallel streamers, the easternmost of which has a<br />

relatively sharp outer edge. In the view of the late<br />

Robert Burnham Jr. "the appearance seems to<br />

suggest that this boundary is the edge of a zone<br />

which has been swept clear of nebulosity by the<br />

northward motion of the star." This motion might<br />

also explain the apparent "rippling" of gas ahead<br />

of the star in its present position. If the distance of<br />

1,600 light-years is accepted for AE Aurigae, the<br />

cloud of reflective material extends at least 9<br />

light-years from the star.<br />

AE Aurigae is visible with the naked eye just<br />

northwest of an obvious tight, "hazy" grouping of<br />

suns, the brightest of which are 5th-magni-tude<br />

16,19, and IQ Aurigae. AE Aurigae and its<br />

neighboring asterism, which Sky & Telescope's<br />

Alan M. MacRobert likens to a "leaping minnow,"<br />

lie outside a divine, well-defined brush stroke of<br />

Milky Way. When I train my 10x50<br />

124<br />

binoculars to that part of the sky, I'm surprised to<br />

find the magnitude-7.5 open cluster NGC 1893<br />

(about 1° southeast of the "minnow") pulling my<br />

attention away from AE Aurigae and the nakedeye<br />

asterism. <strong>The</strong> reason for this is obvious. To<br />

the naked eye the asterism looks fuzzy, so<br />

curiosity causes me to raise my binoculars to it.<br />

Once I find the field in my binoculars, the<br />

asterism is no longer fuzzy, but nearby NGC 1893<br />

is, and curiosity takes control once again. (<strong>The</strong><br />

diffuse emission nebula interwoven with NGC<br />

1893 in the photograph on page 122 is IC410.)<br />

Little has been published about IC 405's<br />

visual appearance. Burnham discusses only its<br />

physical and photographic qualities. <strong>The</strong> most<br />

descriptive discussion known to me appears in<br />

MacRobert's book Star-Hopping for Backyard<br />

Astronomers. <strong>The</strong>re he writes, "In moderately<br />

large amateur telescopes the 'flames' appear as a<br />

large vague glow toward the star's east and north<br />

about 20' across. To my surprise, [my] 6-inch<br />

seemed to show hints of it despite the light<br />

pollution. Quite a catch!" Roger Clark lists IC<br />

405's apparent magnitude as 10.0 in his Visual<br />

Astronomy of the Deep Sky, and he suggests that<br />

relatively low powers (20x for a 6-inch telescope<br />

and 41x for a 12-inch) are best for viewing it. I<br />

found it to shine at magnitude 9.2 in the 4-inch at<br />

23x; this magnitude applies to the reflection<br />

nebula, described by MacRobert, that lies<br />

immediately east and north of AE Aurigae.<br />

Given its diffuse nature, IC 405 would seem<br />

to be a visual challenge, but it isn't. Most<br />

surprisingly, from Hawaii the object reveals itself<br />

in 10x50 binoculars as a faint puff of vapors<br />

southeast of AE Aurigae; averted vision is<br />

required, however. In the 4-inch at 23x the glow<br />

breaks down into finer details, but this requires<br />

intermittent viewing over a period of at least an<br />

hour. I find it helpful to gently<br />

Deep-Sky Companions: <strong>The</strong> <strong>Caldwell</strong> <strong>Objects</strong>

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