A phenomenon is an observable event that can be seen, felt, tasted, or otherwise experienced. The term is used in various contexts, including philosophy, science, and everyday language. In philosophy, Immanuel Kant popularized the word phenomenon when he contrasted it with the noumenon, which cannot be directly observed. In science, a phenomenon refers to any event that is observable, including the use of instrumentation to observe, record, or compile data. Examples of natural phenomena include gravity, tides, moons, planets, volcanic lightning, starling swarms, ant armies, sandstorms, biological processes, and oscillation. Social phenomena are those that occur or exist through the actions of groups of humans, such as six degrees of separation. In everyday language, a phenomenon often refers to an extraordinary event or occurrence that at first defies explanation or baffle the observer.