Horse Head Nebula

The Horsehead Nebula (also Barnard 33) is a small dark nebula in Orion. The nebula is located just to the south of Alnitak, the easternmost star of Orion’s Belt, and is part of the much larger Orion molecular cloud complex.

Imaging this target I got very prominent diffraction spikes from Alnitak, as well as a strong halo around that star (both defects are visible in the bottom left corner of the picture). In some frames the image is also spoiled by an internal reflection, probably linked to Alnitak. While investigating those issues, I provide below a calibrated and cropped drizzled stack of eight frames of 5mn each, amounting to 40mn of integration in Ha.

Since Moana is not a symmetrical design (camera on one side), internal reflections from one particular star can be minimized by changing the side of the meridian from which the target is imaged. Alternatively a focuser baffle or even a “dew shield” might be needed.

The diffraction spike can be very easily removed with my original Radon transform diffraction spike removal script.

The halos will demand an upgrade to Chroma or Astrodon filter at some point. This is a known issue linked to the cheaper Baader filters.

The Horse head nebula in Orion in H Alpha.

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