Abell 21

This large planetary nebula is more of a ragged, asymmetric set of vast gaseous arcs strewn across the outer shell of a little dying star’s former atmosphere. The star is tiny, and shining with an extremely hot blue colour (at magnitude 15.9). If you look carefully, you can see the little blue dot at the centre of the arc. The picture reveals some blue oxygen and hydrogen (beta) emission nearer the centre and more reddish strands further out – presumably hydrogen (alpha) and some sulphur ions. This nebula is known as the Medusa nebula (Abell 21, PK205+14.1) and is located in the South of Gemini. I see Barnfield Bob (see friends) has beaten me to blog an image of this. His optics and tracking are quite superior to the twenty inch I use. Still, I think this stack of about 20 minute-long snaps (+ flats & darks) has revealed a lot of detail in this object. I have tried imaging this object before several times and not been happy with the result on the non-converted camera and unguided scope. I have seen it visually in the scope, and it is quite impressive (the scope is the impressive thing!). It was relatively easy when high in the sky on a dark winter’s night, although an Ultra High Contrast filter was necessary to reveal the ghostly, filamentary details.