Xi Scorpii & Struve 1999 -- Multiple Star System in Scorpius
Xi Scorpii -- Five Star System
I learned that Xi Scorpii was a five-star-system by reading Sue French’s Deep-sky
Wonders in my June 2018 issue of Sky and Telescope.  I had known that Xi Scorpii
was a pretty double-double star in Scorpius but did not know that the brightest
member of the system was itself a double that could be separated in amateur
telescopes under good conditions.  This morning the sky was not all that stable, and
after giving up on getting a decent drawing of Mars, swung the telescope to Xi Scorpii.  
The pretty double-double was there to greet me at low power, but no hint that the
brightest component of the system was also a double.  Finally, at a much higher power,
I was able to see that the primary star was bulging.  I waited patiently for short periods
of atmospheric stability which were long in coming and lasted for only a second or so. I
came close, but I do not believe I ever saw the two-stars cleanly split, just two dots
touching each other.  Sue French, in her article says the separation is 1.1 arcseconds,
which is easily within reach of my 6-inch refractor.  Either the separation is less than
the stated 1.1 arcseconds or (the most likely explanation) the atmosphere was not
stable enough for me to cleanly separate the two stars.