An astronomical unit (au) is equal to the average distance from earth to the sun, about 92. 9 × 10^6 mi. A parsec (pc) is the distance at which a length of 1 au would subtend an angle of exactly 1 second of arc (the figure). A light-year (ly) is the distance that light, traveling through a vacuum with a speed of 186000 mi/s, would cover in 1. 0 year. Express the earth–sun distance in (a) parsecs and (b) light-years.