Friday 13 July 2018

M21: Young and bright

Another pretty and well-known star cluster in Sagittarius is M21, only half a degree away from the famous Trifid Nebula. Containing only 57 confirmed members, it's not as well populated as M23, but nevertheless it's a beautiful object in binoculars and small telescopes. As was the case with M23, the binoscope magnifies just a bit too much to frame this cluster nicely and you're almost getting the impression that you're looking though it. Still, it lies 4,200 light-years away from us, double the distance to M23 and in fact not all that far from the Trifid. Therefore most of its stars appear somewhat dim, although a bright blue supergiant, ten times our Sun's diameter and radiating 64,000 times as much energy, stands out centrally. Many cluster members also appear to be close binaries so in reality the total star count should be a bit higher. 

Interesting to note is that this cluster's still extremely young, hardly 4.6 million years old and therefore not much older than the human species.  

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