The star (other than the Sun) that is closest to Earth is Proxima Centauri. Its distance from Earth can be measured using parallax. Parallax is half the apparent angular shift of the star when observed from Earth at points on opposite sides of the Sun. The parallax of Proxima Centauri is 769 milli arc seconds. How far away is Proxima Centauri? (Give your answer in light-years with the correct number of significant digits.)