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,
PC strand T 5224, American Standard ASTM A416, British standard BS 5896 and the Japanese standard JIS G3536, the Australian standard AS / NZS 4672, Brazilian standard NBR-7483 3, http://www.pcstrand.cn/f694801/What's-PC-STRAND.htm PC strand PC Strand, or prestressed concrete steel strand, is a twisted steel cable composed of 2, 3, 7 or 19 high strength steel wires and is stress-relieved (stabilized) for prestressed concrete or similar purposes. PC strand is classified according to the number of steel wires in a strand: 2 wire strand, 3 wire strand, 7 wire steel strand and 19 wire steel strand. It can be classified according to the surface