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,
Pace (unit) it was standardized as the distance of two steps (') or five Roman feet ('), about . There were 1000 paces in the Roman mile, which was named after that distance as the ' or '. The Byzantine pace (, "bḗma") was an adaption of the Roman step, a distance of 2½ Greek feet. The double pace (, "bḗma diploûn"), meanwhile, was similar to the Roman unit, comprising 5 Greek feet. The Welsh pace () was reckoned as 3 Welsh feet of 9 inches and thus may be seen as similar to the English yard: 3 paces made up a