The nebula itself is not visible, but the point in the sky where it was reported as most clearly visible during December
A nebula discovered in 1868 by Otto Wilhelm von Struve, and subsequently confirmed and added to the New General Catalogue with the catalogue number NGC 1554. Struve considered that the nebula was particularly noteworthy, but modern observations of its recorded coordinates (04h22 +19°36) reveal no nebula at all at that location, hence its description as Struve's 'Lost' Nebula.
The most direct explanation for the nebula's apparent disappearance would be simple error. There is indeed a prominent nebula in the same field of the sky (Hind's VariableNebula, NGC 1555) and conceivably the lost nebula was simply a misidentification of that object, or perhaps some other nearby phenomenon.
The reticle on this image marks the theoretical location of Struve's Lost Nebula, though there is no nebula to be seen at that location. The object on the image's southern edge is Hind's VariableNebula, NGC 1555, which is often suggested as a candidate identity for the lost nebula. Imagery provided by Aladin sky atlas
A more interesting possibility is that the nebula represents a transient event that actually was observed by Struve and his contemporaries, but has now vanished from the sky, something that is by no means impossible. Indeed, the variablenebula to the south shows continuously shifting patterns as it reflects the variable light of the star T Tauri and, conceivably, some similar effect may have temporarily illuminated part of a dark cloud to produce a reflection nebula that was visible in the 1860's, but has now been lost to view.
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