light hour - the distance light travels in a vacuum in one hour; approximately one billion kilometers. 1  astronomy unit - a linear unit used for astronomical distances. 2  light year, light-year - the distance that light travels in a vacuum in 1 year; 5.88 trillion miles or 9.46 trillion kilometers.
keystone. n. 1. (Building) Also called: headstone or quoin the central stone at the top of an arch or the top stone of a dome or vault.2. something that is necessary to connect or support a number of other related things.(ËkiËstoÊn). n.eystone. n. 1. (Building) Also called: headstone or quoin the central stone at the top of an arch or the top stone of a dome or vault.
The Keystone Pipeline System is an oil pipeline system in Canada and the United States, commissioned since 2010.It runs from the Western Canadian Sedimentary Basin in Alberta to refineries in Illinois and Texas, and also to oil tank farms and oil pipeline distribution center in Cushing, Oklahoma.he Keystone Pipeline System is an oil pipeline system in Canada and the United States, commissioned since 2010.