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 mission of this website is to promote the understanding and implementation of the Precautionary Principle for the management of new and emerging risks. The judgement of plausibility should be grounded in scientific analysis. Analysis should be ongoing so that chosen actions are subject to review.he Precautionary Principle is a strategy to cope with possible risks where scientific understanding is yet incomplete, such as the risks of nano technology, genetically modified organisms and systemic insecticides. The Precautionary Principle is defined as follows: