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,
Expansion of the universe an observer it appears that space is expanding and all but the nearest galaxies are receding into the distance. During the inflationary epoch about 10 of a second after the Big Bang, the universe suddenly expanded, and its volume increased by a factor of at least 10 (an expansion of distance by a factor of at least 10 in each of the three dimensions), equivalent to expanding an object 1 nanometer (10 m, about half the width of a molecule of DNA) in length to one approximately 10.6 light years (about 10 m or 62 trillion miles) long. A much