Speed of light they appeared 13 billion years ago, when the universe was less than a billion years old. The fact that more distant objects appear to be younger, due to the finite speed of light, allows astronomers to infer the evolution of stars, of galaxies, and of the universe itself. Astronomical distances are sometimes expressed in light-years, especially in popular science publications and media. A light-year is the distance light travels in one year, around 9461 billion kilometres, 5879 billion miles, or 0.3066 parsecs. In round figures, a light year is nearly 10 trillion kilometres or nearly 6 trillion miles. Proxima Centauri,
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.