Current and future Heliophysics System Observatory missions in their approximate regions of study.
The term heliophysics was coined in 1981 to denote the physics of the entire Sun: from centre to corona. It is a direct translation from the French héliophysique, which was introduced to provide a distinction from physique solaire (solar physics) which in practice was then confined to only the outer layers of the Sun. It is a subdiscipline of heliology. Recently the meaning of the term has been extended by Dr George Siscoe of Boston University to include the physics of the heliosphere (the space around the sun beyond the corona, in principle out to the shock where the solar wind encounters the interstellar medium, but excluding the planets and other condensed bodies). It has subsequently been used by the NASA Science Mission Directorate to encompass the study of the heliosphere and the objects that interact with it—most notably, but not limited to, planetary atmospheres and magnetospheres, the solar corona, and the interstellar medium. Heliophysics combines several other disciplines, including several branches of space physics, plasma physics, and solar physics, including stellar physics in general. The recent extension of heliophysics is closely tied to the study of space weather and the phenomena that affect it, and consequently to climatology. To quote George Siscoe from a recent conference presentation:
Heliophysics is an environmental science, a unique hybrid between meteorology and astrophysics. It comprises a body of data and a set of paradigms (general laws—perhaps mostly still undiscovered) specific to magnetized plasmas and neutrals in the heliosphere interacting with themselves and with gravitating bodies and their atmospheres.
"Heliophysics" is the name of one of four divisions within NASA's Science Mission Directorate (Earth Science, Planetary Science, Heliophysics, and Astrophysics. The word was used to simplify the name of the "Sun--Solar-System Connections" Division (and before that, the "Sun-Earth Connections" Division). There is some controversy behind the naming of this division: the prefix "helio" (Attic Greek: helios) means sun; the term "Heliophysics" literally means "Physics of the Sun", which, therefore, does not adequately describe the majority of the science that is conducted within NASA's Heliophysics division. NASA adopts terminology in many ways.