This composite of two images compares slitless spectroscopy of two well-known planetary nebulae, NGC6543 (Cat's Eye Nebula) at the top, and NGC6720 (M57 Ring Nebula) below. In a spectograph the light is dispersed into its constituent colours. If a target emits light at all wavelengths (such as the star at the centre of each nebula) then it is transformed into a horizontal line and all those colours add up to appear white to our eyes. Planetary nebulae, however are special because they emit at very specific individual wavelengths. Each of the emission lines creates a seperate image in the instrument, so that we get multiple overlapping images of the nebula at each wavelength. The particular wavelengths a nebula emits identify the gases of which it consists. In the case of these two nebulae, the brightest emissions are the red hydrogen-alpha and green oxygen - II lines. The observations were obtained robotically using the Liverpool Telescope and the SPRAT spectograph. As competition judge Melanie Vandenbrouck wrote, 'this picture tells us that data can be beautiful. It is as compelling visually as it is scientifically, revealing the mechanicss of astrophysical knowledge in a minimalist yet stunnigly attractive way'. Born digital photograph entitled 'Iridis', by Robert Smith, taken on 9th April 2016, with the Liverpool Telescope, Andor iDus 420 camera The observations were obtained robotically using the Liverpool Telescope and the SPRAT spectrograph Winner of the Robotic Scope in Astronomy Photographer of the Year 2016.
Artist: Robert Smith
- Image reference: RSM0001
- National Maritime Museum, Greenwich, London. Courtesy of the artist
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