NEBULAE
The Great Lacerta Nebula
— Sh2-126 · wide field —
Processed by Nicolas Rolland, Paris. 28.3 hours gathered at IC Astronomy Observatory, Oria, Spain.
Sh2-126 is one of the largest emission nebulae in Lacerta and one of the hardest to see. This frame is 5.28 degrees on a side, wide enough to hold the whole filament in a single field — which is why it was shot through a 106 mm refractor rather than anything longer.
A five-degree filament in southern Lacerta
The nebula sits in the southern part of Lacerta, about one degree west of the star 10 Lacertae. It has the shape of a long, ragged filament rather than a compact cloud, and it is far below naked-eye reach: this is an object that exists almost entirely in photographs. Through anything other than an H-alpha filter, very little of it registers at all.
Lit by a single star
10 Lacertae is a blue variable of magnitude 4.8 and spectral type O9V, and it is what makes the nebula visible. One star ionises this entire structure — the ultraviolet light it puts out strips electrons from the hydrogen around it, and the faint red glow that a camera records is that hydrogen recombining. Take the star away and the gas is still there; there is simply nothing to reveal it.
Why this field is rarely photographed whole
Five degrees is wider than most deep-sky setups can frame, so Sh2-126 is usually photographed in pieces or cropped to its brightest part. This version covers the region in one frame: 28.3 hours from an FSQ-106ED at f/3.6 under a Spanish sky, of which 7.3 hours went to H-alpha. The brightest knot inside the filament, LBN 437, has its own page shot at four times the depth.
