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.
The main reasons that imperial nations built large naval forces was to protect their economic interests in these colonies as well as their political interests. In addition they also sought to demonstrate their size and prowess in their ability to exert military force around the globe.
A socialist principle would be that there should be no classes at all in a society and that governments should regulate the production and distribution of goods in the best interest of the people.
