Free Astronomy Magazine September-October 2019

53 SEPTEMBER-OCTOBER 2019 SPACE CHRONICLES T his wide-field view cap- tures the evocative and colourful star formation region of the Seagull Nebula, IC 2177, on the borders of the constel- lations of Monoceros (The Uni- corn) and Canis Major (The Great Dog). This view was cre- ated from images forming part of the Digitized Sky Survey 2. [ESO/Digitized Sky Survey 2] minous star called HD 53367 that is 20 times more massive than the Sun, and which we see as the seagull’s piercing “eye”. Sh2-292 is both an emission nebula and a reflection nebula; much of its light is emitted by ionised gas surrounding its nas- cent stars, but a significant amount is also reflected from stars outside it. The dark swathes that interrupt the clouds’ homogeneity and give them texture are dust lanes – paths of much denser material that hide some of the luminous gas behind them. Nebulae like this one have densities of a few hundred atoms per cubic centimetre, much less than the best artificial vacuums on Earth. Nonetheless, nebulae are still much denser than the gas outside them, which has an average density of about 1 atom per cubic centimetre. The Seagull lies along the border between the constel- lations of Canis Major (The Great Dog) and Monoceros (The Unicorn), at a distance of about 3700 light-years in one arm of the Milky Way. Spiral galaxies can contain thousands of these clouds, al- most all of which are concen- trated along their whirling arms. Several smaller clouds are also counted as part of the Seagull Nebula, including Sh2-297, which is a small, knotty addition to the tip of the gull’s upper “wing”, Sh2-292 and Sh2-295. These objects are all in- cluded in the Sharpless Catalogue, a list of over 300 clouds of glowing gas compiled by American astrono- mer Stewart Sharpless. This image was taken using the VLT Survey Telescope (VST), one of the largest survey telescopes in the world observing the sky in visible light. The VST is designed to photo- graph large areas of the sky quickly and deeply. Can you spot the seagull in this photo? We challenge our readers to let their imagination run free and outline the bird in our photo as they see it. Share your pho- tos with the outline of the bird using the hashtag #SpotTheSeagull. ! ing it to glow. This radiation is also the main factor that determines the clouds’ shapes, by exerting pressure on the surrounding material and sculpting it into the whimsical mor- phologies we see. Since each nebula has a unique distribution of stars and may, like this one, be a compos- ite of multiple clouds, they come in a variety of shapes, firing astrono- mers’ imaginations and evoking com- parisons to animals or familiar ob- jects. This diversity of shapes is ex- emplified by the contrast between Sh2-296 and Sh2-292. The latter, seen here just below the “wings”, is a more compact cloud that forms the seagull’s “head”. Its most promi- nent feature is a huge, extremely lu-

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