Monday, 19 August 2019

NGC6645: the ring cluster

Open star clusters are usually more or less ball-shaped with a dense nucleus and peripheral stars scattered around it. Obviously their shape derives from the shape of the gaseous cloud from which they emerged and over time the force of gravity of our galaxy slowly tears them apart, sending the member stars on their lonely journey through adulthood. There are of course several exceptions and I refer to my sketch of Berkeley 4 to show you just one of many examples. But even in this case the stars appear merely "smeared out", which can be explained fairly easily with gravity. 

NGC6645's annular shape, on the other hand, is much more difficult to explain. It gets even more complicated when analysis of 72 of its member stars revealed that this cluster has an age of some 9.7 billion years! Most star clusters don't survive for more than a few hundred thousand up to a billion years, especially when they reside in the gravitational plane of our galaxy. 

Whatever the mechanics behind it, this particular cluster is one of my all-time favourites, not just because of its appearance but also because of its richness and countless starry filaments. I hope that my sketch transmits the emotions it gives me every time I point my telescope at it.

Sunday, 9 June 2019

NGC6543: The Eye of the Cat

For many months observing the night's sky has been somewhat frustrating for me. Unstable air currents kept sweeping over Northern Italy and therefore I was compelled to use low power only. It got so bad that stars looked like little balls, rather than points and it became even hard to resolve the cores of globular clusters. Finally, over a week ago, the sky settled down and I was again able to enjoy the full capabilities of the binoscope. 

This time, I pointed it at the famous "Cat's Eye Nebula", scientifically denominated NGC6543. It's an object that brings back fond memories because it was the first of the "more awkward NGCs" I've ever observed. My first telescope was a modest 60mm refractor and straying off the obvious Messiers seemed almost impossible, especially under my hopelessly light-polluted Flemish sky. The "NGCs", apart from a few exceptions such as the Double Cluster in Perseus, were the realm of serious telescopes and I was told not to even try because deemed too difficult; prone to certain disappointment. 

Now I had this poster of a star map hanging above my bed, which was a source of infinite fascination. For hours I could stare at those stars and the various objects that were highlighted on it. And right there it was, in the constellation of Draco, the dragon: a planetary nebula named "NGC6543". It probably was the sequence of decreasing numbers that caught my attention and I simply couldn't resist. The next clear night I got the telescope out and started searching, hopping from one little star on the map to the next until I should've arrived at the right spot, high in the sky. And there it was! It was tiny, incredibly so, but it was clearly not a star. It was a very small nebula and it stood out wonderfully in the scarcely populated star field. Imagine how proud I was to have risen to the challenge and have tried the "impossible". Also my friends at the Antwerp Observatory were seriously impressed and for me it was also a very important lesson: never give up before you've even started. 

Now, thirty-five years later, this discovery's still very much a part of me and pushes me to hunt for objects that are really considered impossible for humble amateur telescopes. In the meantime, please enjoy this sketch of the Cat's Eye, made with the binoscope at 507x. Gaseous filaments are blown away by the scorching stellar wind of the dying white dwarf star from which they originated, at a speed of 1,900 km/s! X-ray observations revealed that some gaseous filaments reach temperatures of even 1.7 million degrees due to the violent interaction with this stellar wind, which has cleared out the inner bubble of the nebula. The very complex structures around it are still not well understood and may also be caused by a small and still undiscovered companion star. The central star, of which only the core is left (surface temperature 80,000°C!) is about 10,000 times as luminous as our Sun, but will soon start to fade. The overall age of the nebula is estimated at about a thousand years, still pretty young, and will completely dissipate into space within the next 10,000 to 15,000 years. 

The distance of this nebula is estimated to be more or less 3,000 light years.

Sunday, 28 April 2019

NGC4565: the Needle Galaxy

Yes, I know that I've been neglecting my blog recently. My sincere apologies for that. I hope that you understand that I want to enjoy my telescope a bit more instead of getting stressed all the time about making sketches. Loyal readers will know that I spend many hours on each drawing and it was getting a bit too much. 

But here I am again with an image I absolutely wanted to share: the magnificent Needle Galaxy, one of my personal favourites.

It is one of spring's highlights because it's so large and bright and because we see it almost perfectly edge-on, which always makes a galaxy look a bit more special. Other noteworthy examples are M104 and NGC891. A prominent dust lane, situated at the galaxy's edge, appears to cut across the nucleus and divide it in two nearly identical halves. Many books on astronomy use an image of this galaxy as it is generally assumed that our own galaxy looks very much like it when seen from this angle. That being said, the "Needle" is much larger, almost twice the diameter of our Milky Way! 

Distance measurements vary greatly, from 30 to even 50 million light-years, with an average of 39 million.