An astrolabe is a primitive angle-measuring tool. It can be used to - very in-exactly! - measure the altitude above the horizon of a celestial body like the Sun, Moon or Polaris in order to calculate your position.
Medieval gunners used the astrolabe to calculate the height of towers and buildings, in order to more accurately aim their cannons.
American teens have a lot on their minds. Substantial shares point to anxiety and depression, bullying, and drug and alcohol use (and abuse) as major problems among people their age, according to a new Pew Research Center survey of youth ages 13 to 17.
