|Sharpless 2-155 "Cave Nebula": Emission Nebula (Cepheus) RA: 20h 34.1m / DEC: +45° 38'.7|
Instrument: 18-inch Obsession
Having earned a well-known moniker, you would think Sharpless 2-155 (aka Cave Nebula) would be a fine, if not impressive, visual target. Nothing could be further from reality. This is a truly challenging object that is not visible in any aperture under less than very dark skies. My sketch presents a 109X view in the 18-inch Obsession. The 22mm Nagler produces a 45 arcminute diameter true field, much of which is dressed by a gauzy nebulosity. Fitting the widefield eyepiece with an OIII filter produces a better defined view, the one presented at left. 6.5 magnitude HD 216945 anchors the southwest quadrant. There appears to be a noticeably brighter patch of nebulosity immediately south of this star. From here, Sharpless 2-155 spreads north toward a clump of some 20 stars, the brightest of these being 7.7 magnitude HD 217086. Then, the delicate ribbon of light bends to the east and six stars drawn just inside that border. Returning to HD 216945, a broad section of filamentary glow extend to the south. Just below center in my rendering, a patch of foggy light has collected alongside a string of four 10th to 12th magnitude embers. It's all very delicate and subtle, often appearing best to the averted gaze.
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Revised: August 28, 2005 [WDF]