A unit used in the measurement of angles, heavily used particularly in astronomy. Due to ancient Babylonian mathematics, we still divide a circle into 360 even units of arc and call each of these units one degree. The entire sky, therefore, spans 360 degrees. Up to about 180 degrees of sky is visible from any given point on earth with an unobstructed horizon (as measured from, say, east to west, or north to south). The degree is used to make measurements of distance, or position (as with declination) in astronomy. In turn, a degree is composed of 60 minutes of arc, and also of 3600 seconds of arc.