Friday, 2 February 2018

STF867: The joys of double star observing

How can you ever get bored looking at the stars? There are literally billions of them and every single one has its own personal character and story. None, however, show their particular nature as well as binary stars. It's still not clear how many stars are actually double or multiple star systems, but estimates range from 50% for smaller, Sun-like stars to even 80% for massive, hot giants. 

Many of these double stars are a real pleasure to observe, as I've already shown you many times before. Sometimes the challenge is that they're so close together that they're on the limit of what a human observer can distinguish with his amateur telescope. Procyon springs to mind. Others are easier to separate and show the most amazing, contrasting colours, like Ras Algheti. The choice's nearly infinite and I often ask the computer of my telescope to amaze me at random. And then you come across star systems that have hardly been observed by anyone, but who'll mesmerise you with their beauty.

Has anyone of you ever heard of Struve 867? It's just one entry to the enormous list of the famous 19th century German Astronomer. And yet, when my telescope turned to this little star in Orion, I was so charmed that I immediately took my sketchbook. 

The main star is a 7th magnitude white giant that shines 286 solar luminosities at us from the respectable distance of 1,300 light-years. It's companion, only 2.2 arc-seconds apart, appeared orange to me. At magnitude 8.88 it's considerably dimmer and slowly revolves around the main star from a distance of 876 times the distance between the Sun and the Earth (AU or Astronomical Unit). To give you a better idea, that's 25 times the distance from here to Pluto. They only appear almost glued to each other because they're so far away from us. 



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