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.
Sea otters are an example of a keystone species because due to their feeding habits, kelp is allowed to flourish which leads to absorption of high amounts of CO_2, preservation of the organisms which rely on kelp for survival, as well as protecting coastlines. Keystone species are crucial species in an ecosystem. If they were to be removed from an ecosystem, there would a drastic impact on most of the species and the environment within that ecosystem.