The Wizard Nebula in 70 hours

NGC 7380 is a cluster of young stars still inside the cloud that made them, and the Wizard is what that cloud looks like from 8,500 light-years away. This frame is cropped tight — 42 by 64 arcminutes — on the ridges and pillars at the centre, where the gas is being pushed back hardest.

Caroline Herschel found the cluster in 1787; the nebula around it took photography to reveal, and it is catalogued separately as Sh2-142. The cluster spans about 20 light-years and is somewhere between 4 and 11 million years old — young enough that the stars have not yet cleared the material they formed from. Visually it is close to hopeless: very dark skies and an OIII filter, and even then it is a suggestion rather than a shape.

Two O-type stars doing the work

At the centre of the cluster sits DH Cephei, a spectroscopic binary of two massive O-type stars. Between them they supply most of the ultraviolet light that ionises this entire HII region, and most of the wind that sculpts it. The ridges running through this frame are the edges of that pressure — cold gas being compressed on one side and stripped away on the other, which is why the structure reads as walls and pillars rather than as a diffuse cloud.

The colours here are assigned, not real. This is the Hubble palette: SII to red, Ha to green, OIII to blue — three narrowband filters standing in for the three colour channels. A narrowband filter records a single emission line, so what it captures has no natural colour at all until one is given to it. The palette is a reading of the gas rather than a photograph of it: red marks where sulphur dominates, blue where oxygen does, and hydrogen runs through nearly all of it. Seventy hours split almost evenly across the three filters — 152, 121 and 148 ten-minute exposures — is what makes that reading fine enough to trust at full resolution.