M57 planetary nebula in Lyra


 2011 Oct 18

Canon EOS 5D MkII ISO6400 45x30s 254mm Newtonian (2x Barlow, f=2400mm) f/9.6 2011 Oct 18 20:47:08-21:15:15 UT
From Rookhope 54.8N 2.1W 330m asl. Rural, almost no light pollution (3 Bortles)

 2011 Sep 9

Canon EOS 5DMkII 254mm Newtonian @1200mm f/4.8 ISO6400 12x15s 2011-9-9 20:9:16-20:12:41UT
From Rookhope 54.8N 2.1W 330m asl. Rural, almost no light pollution (3 Bortles)

 2009 Aug 15

Canon EOS5DMkII 254mm Newtonian @ 2380mm 20 x 10s f/9.4 ISO12800 2009:8:15 21:57:44-22:04:15 UT
From Whitley Bay 55.1N 1.5W 10m asl. Suburban, significant light pollution (6.5 Bortles)

A star in the constellation of Lyra has jettisoned a shell of gas which has expanded over many centuries until it appears like this, the well-known ring nebula. The star did not completely blow itself apart, so it can still be seen in the centre of the ring, at magnitude 15.2.

My photo has been processed in GRIP to deconvolve it, taking a star image (41 x 41px) as the point spread function, relaxation factor 0.3, for 4 passes.

One thing that interests me about this image is the colour. I have used no filters, nor adjusted the colour balance in any way, so this may be something like the true colour of the nebula (if that is meaningful). It is impossible to see that visually because the eye loses its colour sensitivity in the dark, particularly for such a faint object (the surface brightness of the nebula is published as 9.4). Through the telescope I only see a slightly greenish shape. I am interested to see the red outline, which is shown in some other photographs.

The nebula emits light because it comprises an ionised gas, excited by radiation from the central star but emitting light at the specific frequencies of atomic transitions of the particular ions, as they fall back from the excited states. For this reason it would be possible to photograph the nebula through a filter that cuts out most light pollution. I have such a filter and plan to try it later.

Distance: 1,400 light years, but not known with certainty. It has been estimated that at that distance it would have taken about 20,000 years for the ring to reach its observed size.

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