When you open a door, turn a doorknob, or turn right around a corner, you are making a turn. The size of this rotation is what we call angle. How much did you spin? One full turn: you turn until you look at the same place again. Half turn: you turn your back to where you were looking. Quarter turn: you turn to the side, like a corner. This rotation forms a right angle. Mathematicians divide the entire revolution into 360 equal parts, called degrees (°). So half turn has 180°, and a quarter turn has 90°.