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.
How long is a Keystone Exam administration?There is no time limit for a student to complete a Keystone Exam. Each Keystone Exam should take the typical student 2 to 3 hours to complete. There are two modules on each test, and each module (or Test Session) of the Keystone Exam should take 1 to 1.5 hours to complete.