Parsec Parsec The parsec (symbol: pc) is a unit of length used to measure large distances to astronomical objects outside the Solar System. A parsec is defined as the distance at which one astronomical unit subtends an angle of one arcsecond, which corresponds to astronomical units. One parsec is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about from the Sun. Most of the stars visible to the unaided eye in the night sky are within 500 parsecs of the Sun. The parsec unit was probably first suggested in
Only a Trillion only a trillion. Floyd C. Gale stated that Asimov "[a]lmost certainly had enormous fun writing this collection of articles. He staggers, frightens, amazes and, in two, fiendishly misleads his reader". Following the publication of "Only a Trillion", Asimov compiled several more science essays into the manuscript for another, similar book titled "Only a Light-Year", but that book was never published. Only a Trillion Only a Trillion is a collection of ten science essays and three scientific spoof articles by Isaac Asimov. It was the first collection of science essays published by Asimov. It was first published by Abelard-Schuman in 1957.