N55 – The Eighth-Note Nebula

Beautiful and baffling

Image credit Robert Gendler

RA: 05h 32m 32.9s Dec: -66° 24′ 20″

Diameter: Size 7.0′ x 5.0′

Mag: –

Local OB Association: LH 72

Quite apart for being one of the LMC’s most gorgeous nebulae, N55 is also one of the most baffling objects in the Cloud. How did the small, 170 light-year sized pocket of gas and dust possibly manage to survive all that exploding, and become a standalone nebula in the centre of a vast supergiant shell? It seems to be an unfathomable mystery. But is there anything better than sitting in the dark, staring through one’s telescope and trying to fathom the unfathomable? Credit: ESO

16″ at 228x: One look at N55 and it’s obvious how it came by its nickname, the Eighth-Note Nebula (“eighth-noteʺ is American for the British “quaverʺ). It really does look like a large, bright star-studded quaver – simply gorgeous! It is one of my favourite objects in the Cloud, and I confess to frequently revisiting it under supreme transparency conditions, and lingering for an inordinate amount of time, such is its beauty and fascination… and there is always the chance of a little more to be seen. Even without a filter its pearly-white nebulosity, stretching around 6.5′ and oriented almost N-S is bright and uneven with edges that are misty but distinct. LH 72’s stars appear as a lovely mix of mag 12.5 and fainter stars scattered randomly across the length and breadth of the nebula, with the nebula’s ionising star, beautiful bright white mag 11.5 HD 269722 (OB-type), to the NE, stealing the stellar show. The cluster KMHK 1041, a bright knot of stars lies towards its south-eastern end.

The nebula responds fantastically to the UHC filter and is certainly one of those objects that the longer you look, the more you see. It is made up of four distinct sections. The largest and by far the brightest section is N55A on the southeast side. Circular, 2.5′ in diameter, its nebulosity is beautifully bright and detailed, showing as a delicate patchwork of uneven and asymmetrical glows with lovely edges that fade rapidly in the background sky. Its northwestern end has a large patch of bright nebulosity that is itself knotted in a most delicate way.

An extremely faint nebulosity, picked up with averted vision, connects N55A to the second section of the quaver that lies northwest. This section appears considerably fainter than N55A, ~50″ in diameter and round, its nebulosity a faint mistiness with indistinct edges that fade away gradually. The third section lies further north-northwest and is roundish, smoothly nebulous and ~1.2′ in diameter. It is also connected by the smallest strands of extremely faint nebulosity seen with averted vision. The fourth section lies to its northeast, and is the faintest section; a pale round glow, ~30″ in diameter and detached from the rest of the nebula. HD 269722 lies attached to southern edge of this section. All in all; a dazzling nebula!