Insight Astronomy Photographer of the Year
Winner: Robotic Prize 2016

Iridis © National Maritime Museum, Greenwich, London. Courtesy of the artist (that's me!)
“This picture tells us that data can be beautiful. It is as compelling visually as it is scientifically, revealing the mechanics of astrophysical knowledge in minimalist yet stunningly attractive way.” - Melanie Vandenbrouck (IAPY judging panel)

This composite of two images obtained with the Liverpool Telescope compares slit-less spectroscopy of two well known planetary nebulae, NGC6543 (Cat’s Eye Nebula) at the top, and NGC6720 (M57 Ring Nebula) below. In a spectrograph 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, such as these, only emit light at very specific individual wavelengths. The particular wavelengths a nebula emits identify the gases of which it consists. Here, the brightest emissions are the red hydrogen-alpha and green oxygen-III lines. Each of the emission lines creates a separate image in the instrument showing how the nebula looks at one specific colour. For example, the images caused by hydrogen and helium look very similar, showing these two gases are emitting from the same regions. The oxygen, nitrogen and sulphur however show a very different pattern of emission. A normal image of the nebula is thus decomposed into its individual constituent colours.

Iridis with emission lines labeled
The chemical elements that give rise to each spectral emission line are labeled. The stars emit at all wavelengths, but for NGC6543 a couple of emission lines are seen as bright spots on the solid horizontal trace, arising from highly ionised Helium and Carbon.

The observations were obtained robotically using the Liverpool Telescope and the SPRAT spectrograph. All the data used are publicly available from the LT data archive.

Since the beauty of these images derives from their scientific interpretation as much as their aesthetic appeal, I felt it was very important not to excessively manipulate the images and to preserve their scientific integrity, simply adding the colour tinting to simulate the colours as perceived by the human eye from hydrogen-gamma in the violet through to ionized nitrogen and argon in the deep red. Where the SPRAT detector is able to detect light into the near-infrared which our eyes cannot see, the image was simply left in its native greyscale.

Insight Astronomy Photographer of the Year 2016, attracted over 4500 entries from 80 countries and all seven continents. This year saw the annual competition's first entry from Antarctica! The prizewinners were announced during a ceremony at the Royal Observatory Greenwich with the Liverpool Telescope image, “Iridis”, taking first place in the “Robotic Scope” category. The winning images offer a fascinating cross section of everything that can be considered astrophotography, encompassing pictorial landscape, views through powerful telescopes, highly technical image processing and even social commentary.

The winning entries were seen in a free exhibition at the Royal Observatory in Greenwich which ran until June 2017 and in the Insight Astronomy Photographer of the Year 2016 show, available to planetaria worldwide. Though Iridis is no longer there, a visit to the exhibition every year is very much worth while if you are near Greenwich. All the winners and short listed entries are absolutely spectacular and inspiring both in their artistry and science.

In recognition of the public science outreach work done by both the Royal Observatory Greenwich and the Liverpool Telescope and at the request of the Royal Museums Greenwich, I have now donated the legal title to the image to the National Maritime Museum and it is part of the UK national art collection.

IAPY exhibition at ROG
"Iridis" among the exhibition of winning entries on display at the Royal Observatory Greenwich. © 2016 Kimberly Smith

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