Milliarcsecond (mas) : A unit of angular measure commonly used in astronomy. One milliarcsecond is equal to 0.001 arcsecond, 0.277 77 microdegrees, or 4.848 137 nanoradians
Russ Rowlett (Director), How Many? A Dictionary of Units of Measurement, Center for Mathematics and Science Education University of North Carolina, USA 2005. http://www.unc.edu/~rowlett/units/dictA.html, (Unit of Meas and Covr Factors - Amer) {608}