Tuesday, 13 September 2016

The floating swan

Some astronomical objects are of such rare beauty that I, with my limited writing skills, can't find the right words to describe them. Therefore it's probably best that I let my sketch do the talking for me. M17, aka the Swan Nebula (or also Omega Nebula, although I still don't know why), is one of the brightest star forming regions in our sky and under very good conditions already visible to the naked eye as a brighter knot in the Milky Way. Its structure's also quite similar to that of the famous Orion Nebula, with the difference that we see the Swan edge-on rather than face-on. Buried inside this nebula lies a very young cluster of newborn stars, believed to be only 1 million years old, containing some 800 members. The radiation from these extremely hot baby stars causes the gas cloud, some 15 lightyears in diameter, to glow. The cloud of interstellar matter of which the Swan is but a part, however, is at least 40 lightyears in diameter and has a total mass of 30.000 Suns! Another 1.000 stars are being formed in these outer regions, which in turn are beginning to emit light as well. So we expect that this nebula will still significantly gain in visible size and brightness over the next millennia. Currently, the main nebula does look a bit like a swan, doesn't it? It appears to be floating on a lake of ethereal nebulosity, with its bright "eye" gazing at us. This particular star's often used as a reference by scientists to measure radiation, the distribution of hot gas and the expansion velocity of the nebula. The distance of this nebula complex's estimated to be between 5.000 and 6.000 lightyears.

I can still remember very well the first time that I've looked at this object! It was the end of August 1986 and my family and I were on holiday in the south of France. Obviously I'd brought my telescope with me, which was my loyal 68mm Vixen refractor. One evening I had finally convinced my parents to go for a drive away from the beach and somewhat up in the mountains, so that my brother and I could have a look at the incredibly dark sky that you could still find there. It may have been a coincidence, but one of the first things that I noticed, was this strange little knot in the Milky Way, just above Sagittarius. I immediately pointed my scope at it and there it was. I didn't really see a swan in it back then, more a sort of bright, elongated patch with a kind of a hook at one end. I also couldn't see any of the surrounding nebulosity of course, with my limited instrument and 20mm Kellner eyepiece. But the sketch I made that evening may perhaps still be lying around somewhere at the observatory of Urania, near Antwerp, Belgium. It was the most beautiful sketch I had ever made during my youth and I'll never forget it. It's definitly one of my favourite objects and nearly every summer night when I'm out under the stars I simply must pay it a visit. I hope that you will do so too.

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