Layer 3
(5,000–7,000 light-years)
Moving out to 5,000 light-years, we come to the magnitude 10.5 planetary IC 2149, near 2nd-magnitude Menkalinan (Beta [β] Aurigae). This celestial gnome visually resembles NGC 1514 in that its magnitude 11.3 central star dominates the view, but the comparison stops there. IC 2149’s nebula stretches a mere 8.5" across, appearing as a knotty ring seen almost edge-on. And while this baby blue nebula is 40 percent the size of IC 418, it’s nearly 1.5 times as distant and 1,000 years younger; indeed, the nebula also sports youthful mini-bipolar lobes caught in the process of formation. You’ll want to crank up the power to see this one, but use low power to spy its gentle color.
Now let’s hop a mere 200 light-years farther into space to inspect NGC 7354, a 12th-magnitude celestial introvert. It hides inconspicuously just outside the House of Cepheus asterism, about 31⁄4° north-northeast of Delta Cephei. With a diameter of 22", the nebula has a 3,000-year-old clumpy oval main shell and an older circular outer shell. In the image at right, note the collection of low-excitation bright knots in its equatorial torus. Isn’t it reminiscent of IC 2149? I found the nebula apparent in a 5-inch scope at 60x as a tight and diffuse glow with a bright core and a small outer halo. The annulus opens at magnifications of 180x and more, showing the outer nebula as an egg-shaped glow with a beaded inner ring. The central star glows weakly at magnitude 16.2.
NGC 2440, the Albino Butterfly, is one of the most beautiful planetaries of its kind. At a distance of about 6,200 light-years, this 9th-magnitude beauty is situated about 4½° due south of open star cluster M46 in Puppis, roughly midway between the two preceding planetaries. So within the span of 200 light-years, try to appreciate the subtle differences in each. The butterfly sports an oval torus (with two distinct condensations) and three pairs of white bipolar polyps (the wings) emerging at different places from the nebula’s core. The wings extend farther (30") than NGC 7354’s partly because of its greater age (7,000 years) and closer distance. As with NGC 7354, its high-excitation central star is extremely dim, shining around 18th magnitude. Visible through a 4-inch scope, the bright central shell displays knots and filamentary details that flutter in and out of view with the seeing; the wings are dim extensions that taper like the flame of a candle.
It’s also fun to visually compare the Albino Butterfly with the multiple-shell planetary nebula NGC 2438, which we see projected against M46 in a marvelous chance alignment. By comparison, NGC 2438 lies some 1,600 light-years closer, shines about 1½ magnitudes fainter, and appears about 40" larger — again, partly because of its closer distance, as well as its 12,000-plus-year expansion age for its main shell.