Space weather is the concept of changing environmental conditions in near-Earth space or the space from the Sun's atmosphere to the Earth's atmosphere. It is distinct from the concept of weather within the Earth's atmosphere (troposphere and stratosphere). Space weather is the description of changes in the ambient plasma, magnetic fields, radiation, and other matter in space. Much of space weather is driven by energy carried through interplanetary space by the solar wind from regions near the surface of the Sun and the Sun's atmosphere (chromosphere and corona). The term space weather is sometimes used to refer to changes in interplanetary (and occasionally interstellar) space. Space weather has two focal points: scientific research and applications. The term space weather was not used until the 1990s. Prior to that time, activities now known as space weather were considered to be part of physics or aeronomy or space exploration.