The longest distance unit in common use, the megaparsec is used by astronomers studying the most distant quasars and galaxies. One megaparsec equals one million parsecs, 3.2616 million light years or 30.857 x 1018 kilometers (30.857 zettameters)
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}