Heliophysics is a word coined by Dr. George Siscoe of Boston University and subsequently used by the NASA Science Mission Directorate to encompass the study of the system composed of the Sun's 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. Heliophysics is closely tied to the study of space weather and the phenomena that affect it. 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 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, since the base-word "Helio" means sun. The word "Heliophysics" literally means "Physics of the Sun", which, therefore, does not adequately describe the majority of the science that is conducted within the Heliophysics division. NASA uses this in many other ways.

The field of view (also field of vision, abbreviated FOV) is the extent of the observable world that is seen at any given moment.

Different animals have different fields of view, depending on the placement of the eyes. Humans have an almost 180-degree forward-facing horizontal field of view, while some birds have a complete or nearly complete 360-degree field of view. In addition, the vertical range of the field of view in humans is typically around 100 degrees.

The range of visual abilities is not uniform across a field of view, and varies from animal to animal. For example, binocular vision, which is important for depth perception, only covers 120 degrees (horizontally) of the field of vision in humans^{[citation needed]}; the remaining peripheral 60 degrees have no binocular vision (because of the lack of overlap in the images from either eye for those parts of the field of view). Some birds have a scant 10 or 20 degrees of binocular vision.

Similarly, color vision and the ability to perceive shape and motion vary across the field of view; in humans the former is concentrated in the center of the visual field, while the latter tends to be much stronger in the periphery. This is due to the much higher concentration of color-sensitive cone cells in the fovea, the central region of the retina, in comparison to the higher concentration of motion-sensitive rod cells in the periphery. Since cone cells require considerably brighter light sources to be activated, the result of this distribution is that peripheral vision is much stronger at night relative to binocular vision.