Monday 8 May 2017

My favourite globular

Already as a kid I was seriously obsessed by the night's sky. I remember one night in early December 1984... It was just past three and my parents were fast asleep. Swiftly I got out of bed and began to raise the shutter of the terrace door, which was a tricky thing to do because it squeaked a lot. It wouldn't be the first time that my father came running to my room to give me a good lecture about sleeping and school tomorrow. But this time I didn't hear anyone running down the corridor. There was just my little brother, my loyal partner in crime, who had also woken up and lent me a hand. Right... the shutter was up and the door towards our large terrace was open. I grabbed my 60mm Vixen refractor and manoeuvred it very cautiously through the door. It was too much of a hassle to disassemble it with its equatorial mount so I had to be careful not to hit the door posts with one of the opened tripod's legs. This time I wouldn't be observing from the terrace... risky because too close to my parents' bedroom... so I carried the telescope down the stairs and towards the back of our garden. When I looked up, I saw a sky I hadn't seen before. Orion was about to disappear behind the trees in the west and it was now Leo that ruled the south with the vast and strange constellation of Virgo following closely behind. This was all new to me because usually as from April, when these constellations resplend in the evening, it gets dark late and as such I hadn't had the opportunity to see them yet (school tomorrow... remember?). However, I knew that there was a very interesting object east of Virgo, in a dark corner of the sky that belonged to Serpens Caput, the snake's head: M5. I turned my telescope in the right direction and saw a bright, somewhat grainy patch. My telescope was too small to resolve it into individual stars, but already then I noticed its somewhat irregular shape.

Now, thirty-three years later, M5's still my favourite globular cluster. According to recent estimates it may even contain up to 500.000 stars (!), many of which will easily resolve in a modest telescope. This makes it one of the largest globular clusters known and it is also one of the oldest with an estimated age of 13 billion years. That's about as old as our Universe! At a distance of 24.500 lightyears, it spans some 200 lightyears across. Can you imagine that? Hundreds of thousands of stars in such a confined space! This explains why many stars in globular clusters, notwithstanding the fact that they're among the oldest stars in our Universe and should therefore be cool, red giants, still appear very hot and blue. The extreme proximity of neighbouring stars can literally blow away the stars' atmospheres, exposing their much hotter interior!  

But who cares about all of this theory? Just look at this incredible spectacle and probably you'll understand why I wanted so desperately to sneak out in the middle of the night in order to get a glimpse of it. 

At the bottom you'll find my original sketch of 33 years ago...


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