A Mariner's Astrolabe

The explorers of the 1500's sailed the oceans with only a few simple instruments to guide them. But with these, along with the stars and sun, they were able to navigate the world. They could plot and hold a course, measure their progress, and estimate their position in relation to land.
The astrolabe shown at the left was an instrument used to measure latitude. It has an outer edge divided into degrees, and a movable center bar with pointers on each end. Grasping the astrolabe by the ring at the top, the viewer sighted along the bar, rotating it until one of the pointers aimed at the sun. The figure at the other end indicated the correct latitude. This is the origin of the expression "shooting the sun."