Sunday, 11 March 2018

IC2177 + RCW2/Gum1: The Seagull

On the border between the constellations of Canis Major and Monoceros flies a giant seagull, which astronomers identify as IC2177. Of course we're not talking about a bird but about an enormous hydrogen cloud in which active star formation takes place. This cloud spreads over such a great distance (3° across, the diameter of 6 full Moons!) and its surface brightness is so low that it can be quite challenging to observe visually. Even with my binoscope under a fairly decent sky, the body and wings of the Seagull Nebula merely appeared slightly brighter than the background. The seagull's "head" on the other hand, was more easy to make out around the bright star HD53367 (the "eye"), including some structures and a dark lane that ran from the nebula's centre towards its eastern rim and in which many people see the seagull's beak. 

The star HD53367 is quite interesting in its own right as it shows an unusual pattern in its spectrum. Scientists classify stars with this sort of pattern as "Be stars", more famous examples of which are Gamma Cassiopeiae and especially Achernar on the southern hemisphere. The reason why these stars emit these strange lines in their spectrum is because they spin so rapidly that they not only become very oblate, but that they also expel so much gaseous matter under the centrifugal force that it forms a disk around the star itself. This disk scatters the light from the star in such a way that its spectrum's altered. 

Lying almost 4,000 light-years away from us, the Seagull Nebula is producing literally hundreds of new stars, many of which illuminated the field of view of my telescope like a Christmas tree.



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