December: Celestial Potpourri
The Little Dumbbell Nebula M76, like other planetary nebulae, shows a unique pattern of red hydrogen and blue-green oxygen gaseous shells blown away from the central star. It is just as large as its namesake the Dumbbell Nebula, but resides about five times farther away at a distance of 4,000 light-years. The Little Dumbbell shows a central bar of gas, surrounded by symmetrical semicircular lobes of faint gas. Many planetary nebulae show bilateral symmetry, which in some cases may be related to a binary system. Imaging. Many planetary nebulae are small objects yet rich in color, justifying their inclusion among the Best Targets. A long focal length telescope is suggested for the Little Dumbbell Nebula to yield a small imaging scale and thus high resolution. Steady seeing, accurate tracking, and sharp focusing help to display the clear detail. Routine RGB imaging and single-shot color cameras can yield good results, because most of the faint light of the Little Dumbbell is concentrated into a small area. Luminance layering with a clear filter can help to reveal the dimmer components of the nebula. Processing. Small planetary nebulae need as much detail as possible, because they have to hold the viewer’s interest despite appearing almost lost in the center of an image. Try deconvolution methods after combining your images, but before digital development (DDP) or applying curves. Sharpen the nebula again after your histogram adjustments have revealed the outer lobes of the Little Dumbbell. The central bar is brighter, and thus can tolerate more sharpening than the faint outer loops of gas. Adjust your color balance to show the proper teal color of oxygen and deep red color of hydrogen (Fig. 12.1).